MAX1254现货热卖使用介绍供应商报价哪里找芯片批发报价-中国IC网-芯三七

19-2838; Rev 0; 4/03

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

General Description

Features

o Monitor 10 Signals Without Processor

The MAX1253/MAX1254 are stand-alone, 10-channel (8

external, 2 internal) 12-bit system monitor ADCs with

internal reference. A programmable single-ended/dif-

ferential mux accepts voltage and remote-diode tem-

perature-sensor inputs. These devices independently

monitor the input channels without microprocessor

interaction and generate an interrupt when any variable

exceeds user-defined limits. The MAX1253/MAX1254

configure both high and low limits, as well as the num-

ber of fault cycles allowed, before generating an inter-

rupt. These ADCs can also perform recursive data

averaging for noise reduction. Programmable wait inter-

vals between conversion sequences allow the selection

of the sample rate.

Intervention

o Eight External Channels Programmable as

Temperature or Voltage Monitors

o Intelligent Circuitry for Reliable Autonomous

Measurement

Programmable Digital Averaging Filter

Programmable Fault Counter

o Precision Measurements

12-Bit Resolution

1 ꢀSB IꢁꢀL 1 ꢀSB Dꢁꢀ

0ꢂ.75C Temperature Accuracy ꢃtypꢄ

o Flexible

Automatic Channel Scan Sequencer with

Programmable Intervals

Programmable Inputs: Single Ended/DifferentialL

Voltage/Temperature

At the maximum sampling rate of 94ksps (auto mode,

single channel enabled), the MAX1253 consumes only

5mW (1.7mA at 3V). AutoShutdown^TMreduces supply

current to 190µA at 2ksps and to less than 8µA at 50sps.

Programmable Wait State

o Internal 2ꢂ7V/4ꢂ096V Reference

ꢃMAX1273/MAX1274ꢄ

Stand-alone operation, combined with ease of use in a

small package (16-pin TSSOP), makes the MAX1253/

MAX1254 ideal for multichannel system-monitoring

applications. Low power consumption also makes

these devices a good fit for hand-held and battery-pow-

ered applications.

o Remote Temperature Sensing Up to 10m

ꢃDifferential Modeꢄ

o Single 3V or 7V Supply Operation

o Small 16-Pin TSSOP Package

Applications

Ordering Information

System Supervision

Remote Telecom Networks

Server Farms

PART

TEMP RANGE

-40°C to +85°C

PIN-PACKAGE

16 TSSOP

MAX1253AEUE*

MAX1253BEUE

MAX1254AEUE*

MAX1254BEUE

16 TSSOP

Remote Data Loggers

16 TSSOP

*Future product—contact factory for availability.

Selector Guide

Pin Configuration

TEMP

SUPPLY

TOP VIEW

PART

INL (LSB)

ERROR (5C) VOLTAGE (V)

AIN0

CS

1

2

3

4

5

6

7

8

16

15

1

1.0

3.0

1.0

2.5

MAX1253AEUE*

MAX1253BEUE

MAX1254AEUE*

MAX1254BEUE

2.7 to 3.6

4.5 to 5.5

AIN1

AIN2

AIN3

AIN4

AIN5

AIN6

AIN7

SCLK

14 DIN

13

MAX1253

MAX1254

V

DD

12 GND

11 DOUT

10 INT

*Future product—contact factory for availability.

9

REF

Typical Application Circuit appears at end of data sheet.

16 TSSOP

AutoShutdown is a trademark of Maxim Integrated Products, Inc.

________________________________________________________________ Maxim Integrated Products

1

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

ABSOLUTE MAXIMUM RATINGS

V

to GND .............................................................-0.3V to +6V

Continuous Power Dissipation (T = +70°C)

A

DD

Analog Inputs to GND (AIN0–AIN7, REF) ... -0.3V to (V + 0.3V)

16-Pin TSSOP (derate 8.7mW/°C above +70°C) .........696mW

Operating Temperature Range ...........................-40°C to +85°C

Junction Temperature......................................................+150°C

Storage Temperature Range.............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

DD

Digital Inputs to GND (DIN, SCLK, CS) .... -0.3V to (V

Digital Outputs to GND (DOUT, INT) ........ -0.3V to (V

Digital Outputs Sink Current ............................................. 25mA

Maximum Current into Any Pin .......................................... 50mA

+ 0.3V)

DD

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional

operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to

absolute maximum rating conditions for extended periods may affect device reliability.

ELECTRICAL CHARACTERISTICS

(V

= +2.7V to +3.6V (MAX1253), V

= +4.5V to +5.5V (MAX1254), V

= +2.5V (MAX1253), V = +4.096V (MAX1254), f

REF SCLK

DD

REF

= 10MHz (50% duty cycle), T = T

to T

, unless otherwise noted. Typical values are at T = +25°C.)

MAX A

A

MIN

PARAMETER

DC ACCURACY

Resolution

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

RES

INL

12

Bits

LSB

Grade A

Grade B

1.0

4.0

2.0

Integral Nonlinearity (Note 1)

Differential Nonlinearity

Offset Error

DNL

No missing codes overtemperature

LSB

External reference

Internal reference

LSB

Gain Error (Note 2)

%FSR

ppm/°C

Offset Error Tempco

5

2

External reference

Internal reference

Gain and Temperature Coefficient

Channel-to-Channel Offset Matching

ppm/°C

30

0.1

LSB

%

V

DD

Monitor Accuracy

Internal reference

2.5

DYNAMIC ACCURACY

(10kHz sine-wave input, 2.5V

(MAX1253), 4.096V

SINAD

(MAX1254), 64ksps, f = 10MHz, bipolar input mode)

SCLK

P-P

Signal-to-Noise Plus Distortion

Total Harmonic Distortion

Spurious-Free Dynamic Range

Full-Power Bandwidth

70

-76

72

dB

THD

Up to the 5th harmonic

SFDR

dB

-3dB point

1

MHz

kHz

Full Linear Bandwidth

S / (N + D) > 68dB

100

CONVERSION RATE

Voltage measurement, all ref modes

Temp-sensor ref modes 01, 10

Temp-sensor ref mode 00

10.6

46

11.7

50.7

80

Conversion Time (Note 3)

t

µs

CONV

73

Single-Channel Throughput

Power-Up Time

Manual trigger, voltage measurement

Internal reference (Note 4)

70

0

ksps

µs

t

40

45

PU

ANALOG INPUT

(AIN0–AIN7)

Unipolar, single-ended, or differential inputs

Bipolar, differential inputs

+V

REF

Input Voltage Range (Note 5)

V

-V

/ 2

+V

/ 2

REF

Common-Mode Range

Differentially configured inputs

0

V

DD

Common-Mode Rejection

Differentially configured inputs, V = 0 to V

-90

dB

CM

DD

2

_______________________________________________________________________________________

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

ELECTRICAL CHARACTERISTICS (continued)

(V

= +2.7V to +3.6V (MAX1253), V

= +4.5V to +5.5V (MAX1254), V

= +2.5V (MAX1253), V = +4.096V (MAX1254), f

REF SCLK

DD

REF

= 10MHz (50% duty cycle), T = T

to T

, unless otherwise noted. Typical values are at T = +25°C.)

MAX A

A

MIN

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

µA

Input Leakage Current

On-/off-leakage, V = 0 or V

IN

1

DD

Input Capacitance

(Note 6)

18

pF

TEMPERATURE MEASUREMENTS

T

= -20°C to +85°C

= -40°C to +85°C

= +25°C

0.5

0.75

0.3

1.2

0.7

1.2

0.7

2

1.0

1.5

A

Grade A

MAX1253

MAX1254

Internal Sensor Measurement Error

(Note 7)

= -40°C to +85°C

= +25°C

2.5

3.0

°C

Grade B

MAX1253

= -40°C to +85°C

= +25°C

Grade B

MAX1254

T

= -40°C to +85°C

= +25°C

A

Differential

1

External Sensor Measurement

Error (Note 8)

°C

= -40°C to +85°C

= +25°C

5

Single ended

2

Differentially configured inputs and internal

sensor

0.3

Temperature Measurement Noise

Single-ended configured, external sensor

0.1

0.125

4

Temperature Resolution

°C/LSB

Low

External Sensor Bias Current

µA

High

66

Differentially configured inputs and internal

sensor

0.3

0.1

Power-Supply Rejection

PSR

°C/V

Single-ended configured, external sensor

INTERNAL REFERENCE

MAX1253

MAX1254

Grade A

Grade B

2.456

4.024

2.500

4.096

8

2.544

4.168

REF Output Voltage

V

REF

REF Temperature Coefficient

REF Output Resistance

REF Output Noise

TC

ppm/°C

kΩ

REF

30

7

MAX1253

MAX1254

MAX1253

MAX1254

200

160

-70

µV

RMS

-50

REF Power-Supply Rejection Ratio

PSRR

dB

EXTERNAL REFERENCE

REF Input Voltage Range

V

1.0

V

+ 0.05

DD

V

REF

V

= +2.5V; f

= 94ksps

15

40

1

REF

SAMPLE

REF Input Current

I

µA

REF

In power-down

_______________________________________________________________________________________

3

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

ELECTRICAL CHARACTERISTICS (continued)

(V

= +2.7V to +3.6V (MAX1253), V

= +4.5V to +5.5V (MAX1254), V

= +2.5V (MAX1253), V = +4.096V (MAX1254), f

REF SCLK

DD

REF

= 10MHz (50% duty cycle), T = T

to T

, unless otherwise noted. Typical values are at T = +25°C.)

MAX A

A

MIN

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

DIGITAL INPUTS

Input Voltage Low

Input Voltage High

Input Hysteresis

(SCLK, DIN, CS)

V

x 0.3

DD

V

IL

V

x 0.7

DD

IH

V

200

2

mV

µA

pF

HYST

Input Leakage Current

Input Capacitance

I

IN

V

= 0 or V

DD

10

IN

C

IN

DIGITAL OUTPUTS

(INT, DOUT)

I

= 8mA, DOUT

= 2mA, INT

0.5

SINK

Output Voltage Low

V

OL

SINK

= 8mA, DOUT

= 2mA, INT

V

- 0.5

SOURCE

DD

Output Voltage High

V

OH

Tri-State Leakage Current

Tri-State Output Capacitance

POWER REQUIREMENTS

I

CS = V

10

µA

pF

L

DD

C

5

OUT

MAX1253

2.7

4.5

3.6

5.5

3.3

2.9

2.2

5.0

4.0

3.0

Positive Supply Voltage

V

DD

MAX1254

MAX1253 internal reference (Note 9)

MAX1253 internal reference (Note 10)

MAX1253 external reference (Note 10)

MAX1254 internal reference (Note 9)

MAX1254 internal reference (Note 10)

MAX1254 external reference (Note 10)

Both internal reference, mode 01 (Note 11)

mA

Supply Current

I

DD

8

µA

nA

MAX1253

Full power-down state

MAX1254

480

860

0.4

Full Power-Down Supply Current

Power-Supply Rejection Ratio

I

SHDN

PSRR

Analog inputs at full scale (Note 12)

1.6

mV/V

4

_______________________________________________________________________________________

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

TIMING CHARACTERISTICS

(V = +2.7V to +3.6V (MAX1253), V = +4.5V to +5.5V (MAX1254), T = T

to T , unless otherwise noted.) (Figures 1, 2, and 4)

MAX

DD

A

MIN

PARAMETER

SYMBOL

CONDITIONS

MIN

100

45

25

0

TYP

MAX

UNITS

ns

SCLK Clock Period

t

0.5

CP

CH

SCLK Pulse Width High Time

SCLK Pulse Width Low Time

DIN to SCLK Setup Time

DIN to SCLK Hold Time

CS Fall to SCLK Rise Setup

SCLK Rise to CS Rise Hold

SCLK Fall to DOUT Valid

CS Rise to DOUT Disable

CS Fall to DOUT Enable

CS Pulse Width High

t

ns

t

ns

CL

DS

DH

ns

t

ns

t

25

50

ns

CSS

CSH

DOV

DOD

t

ns

t

C = 30pF

50

40

ns

L

t

C = 30pF

L

ns

t

C = 30pF

L

ns

DOE

CSW

t

40

ns

Note 1: Relative accuracy is the deviation of the analog value at any code from its theoretical value after the gain and offset errors

have been calibrated.

Note 2: Offset nulled.

Note 3: In reference mode 00, the reference system powers up for each temperature measurement. In reference mode 01, the ref-

erence system powers up once per sequence of channels scanned. If a sample wait <80µs is programmed, the reference

system is on all the time. In reference mode 10, the reference system is on all the time (see Table 7).

Note 4: No external capacitor on REF.

Note 5: The operational input voltage range for each individual input of a differentially configured pair (AIN0–AIN7) is from GND to

V

DD

The operational input voltage difference is from -V

/2 to +V

REF

/2.

REF

.

Note 6: See Figure 3 and the Sampling Error vs. Input Source Impedance graph in the Typical Operating Characteristics section.

Note 7: Grade A tested at +10°C and +55°C. -20°C to +85°C and -40°C to +85°C specifications guaranteed by design. Grade B

tested at +25°C. T

to T

specification guaranteed by design.

MIN

MAX

Note 8: External temperature measurement mode using an MMBT3904 (Diodes Inc.) as a sensor. External temperature sensing

from -40°C to +85°C; MAX1253/MAX1254 held at +25°C.

Note 9: Performing eight single-ended external channels’ temperature measurements, an internal temperature measurement, and

an internal V

measurement with no sample wait results in a conversion rate of 2ksps per channel.

DD

Note 10:Performing eight single-ended voltage measurements, an internal temperature measurement, and an internal V

ment with no sample wait results in a conversion rate of 7ksps per channel.

measure-

DD

Note 11:Performing eight single-ended voltage measurements, an internal temperature measurement, and an internal V

ment with maximum sample wait results in a conversion rate of 3ksps per channel.

DD

Note 12:Defined as the shift in the code boundary as a result of supply voltage change. V

= min to max; full-scale input, mea-

DD

sured using external reference.

_______________________________________________________________________________________

5

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

Typical Operating Characteristics

(V

= +3V, V

= 2.5V (MAX1253); V

= 5V, V

= 4.096V (MAX1254); f

= 10MHz, C

= 0.1µF, T = +25°C, unless oth-

DD

REF

DD

REF

SCLK

REF

A

erwise noted.)

INTEGRAL NONLINEARITY

vs. DIGITAL OUTPUT CODE

INTERNAL REFERENCE VOLTAGE

vs. SUPPLY VOLTAGE

DIFFERENTIAL NONLINEARITY

vs. DIGITAL OUTPUT CODE

1.0

0.8

2.510

1.0

0.8

MAX1253

2.509

2.508

2.507

2.506

2.505

2.504

2.503

2.502

2.501

2.500

0.6

0.4

0.2

0

-0.2

-0.4

-0.6

-0.8

-1.0

-0.2

-0.4

-0.6

-0.8

-1.0

0

1024

2048

3072

4096

2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6

SUPPLY VOLTAGE (V)

0

1024

2048

3072

4096

OUTPUT CODE

INTERNAL REFERENCE VOLTAGE

vs. SUPPLY VOLTAGE

REFERENCE VOLTAGE

vs. TEMPERATURE

REFERENCE VOLTAGE

vs. TEMPERATURE

4.085

4.083

4.081

4.079

4.077

4.075

2.510

2.508

2.506

2.504

2.502

2.500

2.498

2.496

2.494

2.492

2.490

4.0900

4.0875

MAX1253

MAX1254

4.0850

4.0825

4.0800

4.0775

GRADE B

GRADE A

4.0750

4.0725

4.0700

GRADE B

4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5

SUPPLY VOLTAGE (V)

-40

-20

0

20

40

60

80

-40

-20

0

20

40

60

80

TEMPERATURE (°C)

SUPPLY CURRENT

vs. SAMPLE RATE

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

SUPPLY CURRENT

vs. SAMPLE RATE

10

1

10

1

INTERNAL REFERENCE

(MODE 01) MAX1254

INTERNAL REFERENCE

(MODE 01) MAX1253

EXTERNAL REFERENCE (MODE 00)

4.2

3.8

3.4

3.0

2.6

2.2

1.8

1.4

1.0

9 TEMPERATURE CHANNELS

AND 1 VOLTAGE CHANNEL

9 TEMPERATURE

CHANNELS AND 1

VOLTAGE CHANNEL

9 TEMPERATURE

CHANNELS AND 1

VOLTAGE CHANNEL

9 VOLTAGE CHANNELS AND

1 TEMPERATURE CHANNEL

(V /2)

DD

0.1

9 VOLTAGE

CHANNELS AND

1 TEMPERATURE

CHANNEL

CHANNELS AND

1 TEMPERATURE

CHANNEL

0.01

0.001

0.01

0.001

1 VOLTAGE CHANNEL

(V /2)

DD

1 VOLTAGE CHANNEL

(V /2)

1 VOLTAGE CHANNEL

(V /2)

DD

0.001

0.01

0.1

1

10

100

0.001

0.01

0.1

1

10

100

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5

SUPPLY VOLTAGE (V)

SAMPLE RATE (kHz)

6

_______________________________________________________________________________________

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

Typical Operating Characteristics (continued)

(V

= +3V, V

= 2.5V (MAX1253); V

= 5V, V

= 4.096V (MAX1254); f

= 10MHz, C

= 0.1µF, T = +25°C, unless oth-

DD

REF

DD

REF

SCLK

REF

A

erwise noted.)

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

SUPPLY CURRENT

vs. TEMPERATURE

SUPPLY CURRENT

vs. TEMPERATURE

2.6

2.5

2.4

2.3

2.2

2.1

2.0

1.9

1.8

1.7

1.6

5.0

4.5

4.0

3.5

3.0

2.5

2.0

INTERNAL REFERENCE (MODE 01)

9 TEMPERATURE CHANNELS

4.3

3.9

3.5

3.1

2.7

2.3

1.9

1.5

INTERNAL REFERENCE (MODE 01) MAX1254

9 TEMPERATURE CHANNELS AND

1 VOLTAGE CHANNEL (V /2)

DD

AND VOLTAGE CHANNEL (V /2)

DD

9 TEMPERATURE CHANNELS AND

1 VOLTAGE CHANNEL (V /2)

DD

9 VOLTAGE

CHANNELS AND

1 TEMPERATURE

CHANNEL

9 VOLTAGE CHANNELS AND

1 TEMPERATURE CHANNEL

9 VOLTAGE CHANNELS AND

1 TEMPERATURE CHANNEL

1 VOLTAGE CHANNEL (V /2)

DD

1 VOLTAGE CHANNEL (V /2)

DD

1 VOLTAGE

CHANNEL (V /2)

DD

INTERNAL REFERENCE (MODE 01) MAX1253

-40 -25 -10 20 35 50 65 80

TEMPERATURE (°C)

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5

SUPPLY VOLTAGE (V)

5

-40 -25 -10

5

20 35 50 65 80

TEMPERATURE (°C)

SHUTDOWN SUPPLY CURRENT

vs. TEMPERATURE

SHUTDOWN SUPPLY CURRENT

vs. SUPPLY VOLTAGE

GAIN AND OFFSET ERROR

vs. SUPPLY VOLTAGE

1.00

0.80

0.60

0.40

0.20

0

SINGLE ENDED

700

600

500

400

300

200

100

0

700

600

500

400

300

200

100

MAX1254

DD

V

= 5V

OFFSET ERROR

MAX1254

MAX1253

-0.20

-0.40

-0.60

-0.80

-1.00

MAX1254

MAX1253

GAIN ERROR

MAX1253

= 3V

V

DD

-40 -25 -10

5

20 35 50 65 80

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5

SUPPLY VOLTAGE (V)

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5

SUPPLY VOLTAGE (V)

TEMPERATURE (°C)

INTERNAL TEMPERATURE SENSOR

TEMPERATURE ERROR

GAIN ERROR vs. TEMPERATURE

OFFSET ERROR vs. TEMPERATURE

1.00

0.90

0.80

0.70

0.60

0.50

0.40

0.30

0.20

0.10

0

1.00

UNIPOLAR

BIPOLAR DIFFERENTIAL

CONFIGURATION

EXTERNAL REFERENCE

MODE

UNIPOLAR SINGLE-ENDED

CONFIGURATION

EXTERNAL REFERENCE

MODE

MAX1253/MAX1254

0.40

0.20

0

DIFFERENTIAL

CONFIGURATION

EXTERNAL

0.80

0.60

0.40

0.20

0

GRADE A INTERNAL

SENSOR

REFERENCE MODE

UNIPOLAR

DIFFERENTIAL

CONFIGURATION

EXTERNAL

BIPOLAR DIFFERENTIAL

CONFIGURATION

EXTERNAL REFERENCE

MODE

-0.20

-0.40

-0.60

-0.80

-0.20

-0.40

REFERENCE MODE

GRADE B INTERNAL

-0.60 SENSOR

UNIPOLAR SINGLE-ENDED

CONFIGURATION

EXTERNAL REFERENCE MODE

-0.80

-0.10

-1.00

-40 -25 -10

5

20 35 50 65 80

-40 -25 -10

5

20 35 50 65 80

-40

-20

0

20

40

60

80

TEMPERATURE (°C)

_______________________________________________________________________________________

7

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

Typical Operating Characteristics (continued)

(V

= +3V, V

= 2.5V (MAX1253); V

= 5V, V

= 4.096V (MAX1254); f

= 10MHz, C

= 0.1µF, T = +25°C, unless oth-

DD

REF

DD

REF

SCLK

REF A

erwise noted.)

EXTERNAL TEMPERATURE SENSOR

TEMPERATURE ERROR

TEMPERATURE ERROR vs. INTERCONNECT

CAPACITANCE (EXTERNAL SENSOR)

2.0

1.6

1

0

MAX1253/MAX1254

1.2

EXTERNAL SENSOR,

DIFFERENTIAL INPUT

-1

-2

-3

-4

-5

-6

0.8

0.4

0

-0.4

-0.8

-1.2

-1.6

-2.0

EXTERNAL DIODE

DIFFERENTIAL TEMPERATURE

MEASUREMENT MODE

EXTERNAL SENSOR,

SINGLE-ENDED INPUT

-40

-20

0

20

40

60

80

10

100

1

1000

TEMPERATURE (°C)

INTERCONNECT CAPACITANCE (pF)

TURN ON THERMAL TRANSIENT,

CONTINUOUS CONVERSION

SAMPLING ERROR

vs. INPUT SOURCE IMPEDANCE

V

= 3.0V

DD

1

0

0.625

0.500

0.375

0.250

0.125

0

IN A TSSOP SOCKET

SOLDER ON A 2in ✕ 2in PWB

-1

-2

-3

-4

-5

IN AN OIL BATH

EXTERNAL BJT

-0.125

10

100

1000

10,000

0

5

10

15

20

25

30

SOURCE IMPEDANCE (Ω)

TIME (s)

8

_______________________________________________________________________________________

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

Block Diagram

V

DD

REF

REFERENCE

INPUT CHANNEL REGISTER

INPUT CONFIGURATION REGISTER

STEP-UP REGISTER

TEMP

SENSOR

MAX1253

MAX1254

ALARM REGISTER

12-BIT

ADC WITH

T/H

AIN1

AIN2

AIN3

AIN4

AIN5

AIN6

AIN7

DOUT

DIN

MUX

SERIAL

INTERFACE

SCLK

CS

SCAN

AND

CONVERSION

CONTROL

AVERAGING

DIGITAL

COMPARATOR

POWER-

GOOD

INT

POR

INTERNAL TEMP

V

/2

DD

AIN0

AIN1

AIN2

AIN3

AIN4

AIN5

AIN6

AIN7

ACCUMULATOR ACCUMULATOR ACCUMULATOR ACCUMULATOR ACCUMULATOR ACCUMULATOR ACCUMULATOR ACCUMULATOR ACCUMULATOR ACCUMULATOR

UPPER

THRESHOLD

UPPER

THRESHOLD

UPPER

THRESHOLD

UPPER

THRESHOLD

UPPER

THRESHOLD

UPPER

THRESHOLD

UPPER

THRESHOLD

UPPER

THRESHOLD

UPPER

THRESHOLD

UPPER

THRESHOLD

LOWER

THRESHOLD

LOWER

THRESHOLD

LOWER

THRESHOLD

LOWER

THRESHOLD

LOWER

THRESHOLD

LOWER

THRESHOLD

LOWER

THRESHOLD

LOWER

THRESHOLD

LOWER

THRESHOLD

LOWER

THRESHOLD

CHANNEL

CONFIGURATION CONFIGURATION CONFIGURATION CONFIGURATION CONFIGURATION CONFIGURATION CONFIGURATION CONFIGURATION CONFIGURATION CONFIGURATION

Pin Description

PIN NAME

FUNCTION

1

2

3

4

5

6

7

8

AIN0 Analog Voltage Input/Temperature Input Channel 0 or Positive Differential Input Relative to AIN1

AIN1 Analog Voltage Input/Temperature Input Channel 1 or Negative Differential Input Relative to AIN0

AIN2 Analog Voltage Input/Temperature Input Channel 2 or Positive Differential Input Relative to AIN3

AIN3 Analog Voltage Input/Temperature Input Channel 3 or Negative Differential Input Relative to AIN2

AIN4 Analog Voltage Input/Temperature Input Channel 4 or Positive Differential Input Relative to AIN5

AIN5 Analog Voltage Input/Temperature Input Channel 5 or Negative Differential Input Relative to AIN4

AIN6 Analog Voltage Input/Temperature Input Channel 6 or Positive Differential Input Relative to AIN7

AIN7 Analog Voltage Input/Temperature Input Channel 7 or Negative Differential Input Relative to AIN6

Positive Reference Input in External Mode. Bypass REF with a 0.1µF capacitor to GND when in external mode.

When using the internal reference, REF must be left open.

9

REF

10

INT

Interrupt Output. Push-pull or open drain with selectable polarity. See Table 9 and the INT Interrupt Output section.

11 DOUT Serial Data Output. DOUT transitions on the falling edge of SCLK. High impedance when CS is at logic high.

12

13

14

GND Ground

Positive Power Supply. Bypass with a 0.1µF capacitor to GND.

DIN Serial Data Input. DIN data is latched into the serial interface on the rising edge of the SCLK.

V

DD

15 SCLK Serial Clock Input. Clocks data in and out of the serial interface (duty cycle must be 40% to 60%).

Active-Low Chip-Select Input. When CS is low, the serial interface is enabled. When CS is high, DOUT is high

impedance, and the serial interface resets.

16

CS

_______________________________________________________________________________________

9

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

V

DD

V

DD

100nA

DOUT

100nA

C

= 100pF

C

= 100pF

C

LOAD

= 100pF

C

= 100pF

LOAD

GND

a) V TO V

GND

b) HIGH-Z TO V AND V TO V

GND

a) V TO HIGH-Z

GND

b) V TO HIGH-Z

OL

OH

OL

OH

OL

OH

OL

Figure 1. Load Circuits for DOUT Enable Time and SCLK to

DOUT Delay Time

Figure 2. Load Circuit for DOUT Disable Time

alarm condition. If desired, the device can be pro-

grammed to average the results of many measurements

before comparing to the threshold value. This reduces

the sensitivity to external noise in the measured signal.

In addition, the user can set the number of times the

threshold is exceeded (fault cycles) before generating

an interrupt. This feature reduces falsely triggered

alarms caused by undesired, random spurious impulses.

Detailed Description

The MAX1253/MAX1254 are precision-monitoring inte-

grated circuit systems specifically intended for stand-

alone operation. They can monitor diverse types of

inputs, such as those from temperature sensors and

voltage signals from pressure, vibration, and accelera-

tion sensors, and digitize these input signals. The digi-

tal values are then compared to preprogrammed

thresholds and, if the thresholds are exceeded, the

processor is alerted by an interrupt signal. No interac-

tion by the CPU or microcontroller (µC) is required until

one of the programmed limits is exceeded (Figures 3

and 4).

When the fault cycle criterion is exceeded, an alarm

condition is created. The device writes the fault condi-

tion into the alarm register to indicate the alarmed input

channel.

Converter Operation

The MAX1253/MAX1254 ADCs use a fully differential

successive-approximation register (SAR) conversion

technique and an on-chip track-and-hold (T/H) block to

convert temperature and voltage signals into a 12-bit

digital result. Both single-ended and differential config-

urations are supported with a unipolar signal range for

single-ended mode and bipolar or unipolar ranges for

differential mode. Figure 5 shows the equivalent input

circuit for the MAX1253/MAX1254. Configure the input

channels according to Tables 5 and 6 (see the Input

Configuration Register section).

Voltages on all the inputs are converted to 12-bit values

sequentially and stored in the current data registers.

Note that eight of these inputs are external and two are

internal. One of the internal inputs monitors the V

DD

voltage supply, while the other monitors the internal IC

temperature. AIN0 to AIN7 can be configured as either

single ended (default) or differential. In addition, these

inputs can be configured for single-ended or differen-

tial temperature measurements. In the temperature

configuration, the device provides the proper bias nec-

essary to measure temperature with a diode-connected

transistor sensor. The user enables which inputs are

measured (both external and internal) and sets the

delay between each sequence of measurements dur-

ing the initial setup of the device.

In single-ended mode, the positive input (IN+) is con-

nected to the selected input channel and the negative

input (IN-) is connected to GND. In differential mode,

IN+ and IN- are selected from the following pairs:

AIN0/AIN1, AIN2/AIN3, AIN4/AIN5, and AIN6/AIN7.

Once initiated, voltage conversions require 10.6µs (typ)

to complete.

The values stored in the current data registers are com-

pared to the user-preprogrammed values in the thresh-

old registers (upper and lower thresholds) and, if

exceeded, activate the interrupt output and generate an

10 ______________________________________________________________________________________

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

V

DD

AIN0

AIN1

AIN2

AIN3

AIN4

AIN5

AIN6

AIN7

INPUT REGISTERS

CURRENT DATA

UPPER THRESHOLD

LOWER THRESHOLD

# FAULT CYCLES

AVERAGE

12-BIT

ADC WITH T/H

DIGITAL

COMPARATOR

INT

MUX

CONFIGURATION/

STATUS

REGISTERS

SCAN AND

CONVERSION

CONTROL

DIN

SERIAL

INTERFACE

DOUT

SCLK

CS

TEMP

SENSE

Figure 3. Simplified Alarm Block Diagram of the MAX1253/MAX1254

During the acquisition interval, IN+ and IN- charge both

a positive (CHOLDP) and a negative (CHOLDN) sam-

pling capacitor. After completing the acquisition inter-

val, the T/H switches open, storing an accurate sample

of the differential voltage between IN+ and IN-. This

charge is then transferred to the ADC and converted.

Finally, the conversion result is transferred to the cur-

rent data register.

Input Bandwidth

The ADC’s input tracking circuitry has a 1MHz small-

signal bandwidth. To avoid high-frequency signals

aliasing into the frequency band of interest, anti-alias

prefiltering of the input signals is recommended.

Analog Input Protection

Internal protection diodes, which clamp the analog

inputs to V

and GND, allow the channel input pins to

DD

Temperature conversions require 46µs (typ) and mea-

sure the difference between two sequential voltage

measurements (see the Temperature Measurement

section for a detailed description).

swing from (GND - 0.3V) to (V

+ 0.3V) without dam-

DD

age. However, for accurate conversions near full scale,

the inputs must not exceed V by more than 50mV or

DD

be lower than GND by 50mV. If the analog input range

must exceed 50mV beyond the supplies, limit the input

current.

Fully Differential Track/Hold (T/H)

The T/H acquisition interval begins with the rising edge

of CS (for manually triggered conversions) and is inter-

nally timed to 1.5µs (typ). The accuracy of the input sig-

nal sample is a function of the input signal’s source

impedance and the T/H’s capacitance. In order to

achieve adequate settling of the T/H, limit the signal

source impedance to a maximum of 1kΩ.

Single Ended/Differential

The MAX1253/MAX1254 use a fully differential ADC for

all conversions. Through the input configuration regis-

ter, the analog inputs can be configured for either dif-

ferential or single-ended conversions. When sampling

signal sources close to the MAX1253/MAX1254, single-

ended conversion is generally sufficient. Single-ended

conversions use only one analog input per signal

source, internally referenced to GND.

______________________________________________________________________________________ 11

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

INCREMENT

CHANNEL

COUNTER

IS CHANNEL

NO

ENABLED?

YES

SAMPLE

CHANNEL

CONVERT

CHANNEL

AVERAGE

CONVERTED

CHANNEL DATA

IS

SAME FAULT

AS PREVIOUS?

INCREMENT

FAULT COUNTER

AVG DATA

> UPPER?

YES

NO

YES

RESET FAULT

COUNTER

IS

AVG DATA

< LOWER?

NO

IS

FAULT CNT

>

FAULT REG?

NO

YES

SET ALARM

REGISTER

Figure 4. Alarm Flowchart

12 ______________________________________________________________________________________

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

V

DD

T

CHOLDP

CHOLDN

CHOLD

8-TO-1

DIFFERENTIAL

MUX

8-TO-1

DIFFERENTIAL

MUX

ADC

H

T

H

TEMP

V

AZ

V

AZ

SINGLE-ENDED INPUT EQUIVALENT INPUT CIRCUIT

DIFFERENTIAL INPUT EQUIVALENT INPUT CIRCUIT

Figure 5. Single-Ended/Differential Input Equivalent Input Circuit

In differential mode, the T/H samples the difference

between two analog inputs, eliminating common-mode

DC offsets and noise. See the Input Configuration

Register section and Tables 5 and 6 for more details on

configuring the analog inputs.

Digital Interface

The MAX1253/MAX1254 digital interface consists of

five signals: CS, SCLK, DIN, DOUT, and INT. CS,

SCLK, DIN, and DOUT comprise an SPI™-compatible

serial interface (see the Serial Digital Interface section).

INT is an independent output that provides an indica-

tion that an alarm has occurred in the system (see the

INT Interrupt Output section).

Unipolar/Bipolar

When performing differential conversions, the input

configuration register (Tables 5 and 6) also selects

between unipolar and bipolar operation. Unipolar mode

Serial Digital Interface

The MAX1253/MAX1254 feature a serial interface com-

patible with SPI, QSPI™, and MICROWIRE™ devices.

For SPI/QSPI, ensure that the CPU serial interface runs

in master mode so it generates the serial clock signal.

sets the differential input range from 0 to V

A nega-

REF.

tive differential analog input in unipolar mode causes

the digital output code to be zero. Selecting bipolar

mode sets the differential input range to

V /2. The

REF

digital output code is straight binary in unipolar mode

and two’s complement in bipolar mode (see the

Transfer Function section).

Select a serial clock frequency of 10MHz or less, and

set clock polarity (CPOL) and phase (CPHA) in the µP

control registers to the same value, one or zero. The

MAX1253/MAX1254 support operation with SCLK idling

high or low, and thus operate with CPOL = CPHA = 0 or

CPOL = CPHA = 1.

In single-ended mode, the MAX1253/MAX1254 always

operate in unipolar mode. The analog inputs are inter-

nally referenced to GND with a full-scale input range

from 0 to V

REF.

SPI and QSPI are trademarks of Motorola, Inc.

MICROWIRE is a trademark of National Semiconductor Corp.

______________________________________________________________________________________ 13

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

CS

t

CSW

t

CSH

t

CH

CSS

t

CP

t

CL

SCLK

DIN

t

DS

t

DH

t

DOD

DOV

HIGH-Z

DOUT

HIGH-Z

t

DOE

Figure 6. Detailed Serial Interface Timing Diagram

Clock pulses on SCLK shift data into DIN on the rising

edge of the SCLK and out of DOUT on the falling edge

of SCLK.

Output Data Format

Output data from the MAX1253/MAX1254 is clocked

onto DOUT on the falling edge of SCLK. Single-ended

and unipolar differential measurements are output in

straight binary MSB first, with two 8-bytes-per-conver-

sion result, and the last 4 bits padded with zeros. For

temperature and bipolar differential voltage measure-

ments, the output is two’s complement binary in the

same 2-byte format. The MSB of the output data from a

read command transitions at DOUT after the falling

edge of the 8th SCLK clock pulse following the CS

high-to-low transition. Table 2 shows the number of

bytes to be read from DOUT for a given read com-

mand.

Data transfers require a logic low on CS. A high-to-low

transition of CS marks the beginning of a data transfer. A

logic high on CS at any time resets the serial interface.

See Figure 6 and the Timing Characteristics table for

detailed serial-interface timing information.

Input Data Format

Serial communications always begin with an 8-bit com-

mand word, serially loaded from DIN. A high-to-low

transition on CS initiates the data input operation. The

command word and the subsequent data bytes (for

write operations) are clocked from DIN into the

MAX1253/MAX1254 on the rising edges of SCLK. The

first rising edge on SCLK, after CS goes low, clocks in

the MSB of the command word (see the Command

Word section). The next seven rising edges on SCLK

complete the loading of the command word into the

internal command register. After the 8-bit command

word is entered, transfer 0 to 20 bytes of data, depend-

ing on the command. Table 2 shows the number of

data bytes for each command.

Command Word

The command word (Table 1) controls all serial com-

munications and configuration of the MAX1253/

MAX1254, providing access to the 44 on-chip registers.

The first 4 MSBs of the command word specify the

command (Table 2), while the last 4 bits provide

address information.

The first rising edge on SCLK, after CS goes low, trans-

fers the command word MSB into DIN. The next seven

rising edges on SCLK shift the remaining 7 bits into the

internal command register (see the Serial Digital

Interface section).

Table 1. Command Word

B7 (MSB)

B6

B5

B4

B3

B2

B1

B0 (LSB)

Command B3 Command B2 Command B1 Command B0

Address B3

Address B2

Address B1

Address B0

14 ______________________________________________________________________________________

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

Table 2. Command Description

DATA BYTES AFTER

COMMAND WORD

COMMAND

WORD

COMMAND DESCRIPTION

BYTES TO

BYTES

DIN

FROM DOUT

0000####

0001xxxx

0010####

0011####

0100####

0101xxxx

0110xxxx

0111xxxx

1000####

1001xxxx

1010####

1011xxxx

1100####

1101xxxx

1110xxxx

1111xxxx

0

3

Manually Trigged Conversion

0

Read Alarm Register

0

2

Read Current Data Register for Selected Channel

Read Current Data Register for All Channels

Read Configuration Register for Selected Channel

Read Global Configuration Registers

Reserved

0

20

5

0

5

N/A

0

N/A

0

Reset

0

Clear Alarm/Fault for Selected Channels

Clear Alarm/Fault for All Channels

Write Current Data Register for Selected Channel

Write Current Data Registers for All Channels

Write Configuration Registers for Selected Channel

Write Global Configuration Registers

Reserved

0

2

0

20

5

0

5

0

N/A

Reserved

#### = Channel address code, see Table 3.

xxxx = These bits are ignored for this command.

Manually Triggered Conversion

Table 3. Channel Address

(Command Code = 0000)

Before beginning a manual conversion, ensure the

scan mode bit in the setup register is zero, because a

logic 1 disables manual conversions. The address bits

in a Manually Triggered Conversion command select

the input channel for conversion (see Table 3). When

performing a differential conversion, use the even chan-

nel address (AIN0, AIN2, AIN4, AIN6); the command is

ignored if odd channel addresses (AIN1, AIN3, AIN5,

AIN7) are used for a differential conversion.

ADDRESS IN COMMAND

INPUT

0000

0001

0010

0011

0100

0101

0110

0111

1000

1001

1010

1011

1100

1101

1110

1111

Internal temperature

VDD

AIN0

AIN1

AIN2

AIN3

AIN4

After issuing a Manually Triggered Conversion com-

mand, bring CS high to begin the conversion. To obtain

a correct conversion result, CS must remain high for a

period longer than the reference power-up time (if in

power-down mode) plus the conversion time for the

selected channel configured conversion type (voltage

or temperature). The conversion’s result can then be

read at DOUT by issuing a Read Current Data Register

for Selected Channel command, addressing the con-

verted channel. See Table 3 for channel addresses.

AIN5

AIN6

AIN7

Reserved

______________________________________________________________________________________ 15

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

Read Alarm Register

(Command Code 0001)

The Read Alarm Register command, 0001, outputs the

current status of the alarm register (see Table 11). The

address bits in this command are ignored. The alarm

register is 24 bits long and outputs in 3 bytes. Table 12

illustrates the encoding of the alarm register.

Read Current Data Register for All

Channels (Command Code 0011)

The Read Current Data Registers for All Channels com-

mand, 0011, outputs the data in the current data regis-

ters of all 10 channels starting with the internal

temperature sensor, then the V

monitor, followed by

DD

AIN0 to AIN7. The address bits following this command

are ignored. It takes 20 bytes to read all of the 10 chan-

nels’ current data registers.

After receiving an interrupt, read the alarm register to

determine the source of the interrupt (see the Alarm

Register section).

Read Configuration Register for Selected

Channel (Command Code 0100)

Read Current Data Register for Selected

Channel (Command Code 0010)

The Read Configuration Register for Selected Channel

command, 0100, outputs the configuration data of the

channel selected by the address bits (see Table 3).

The first register that shifts out is the upper threshold

register (2 bytes), followed by the lower threshold regis-

ter (2 bytes), ending with the channel configuration reg-

ister (1 byte), all MSB first. It takes 5 bytes to read all

three registers. See the Channel Registers section for

more details.

The Read Current Data Register for Selected Channel

command, 0010, outputs the data in the current data

register of the selected channel. The address bits fol-

lowing this command select the input channel to be

read (see Table 3). The current data register is a 12-bit

register. It takes 2 bytes to read its value. See the

Output Data Format and Current Data Registers sec-

tions for more details. See Table 3 for channel address-

es. Also, see Figure 7.

CS

SCLK

DIN

C3 C2 C1 C0 A3 A2 A1 A0

DOUT

D11

D10 D9 D8 D7 D6 D5 D4

D3

D2 D1 D0

Figure 7. Serial Register Read Timing

16 ______________________________________________________________________________________

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

Read Global Configuration Register

(Command Code 0101)

Clear Alarm Register for All Channels

(Command Code 1001)

The Read Global Configuration Register command,

0101, outputs the global configuration registers. The

address bits following this command are ignored.

When the MAX1253/MAX1254 receive a read global

configuration register command, they output 5 bytes of

data: 2 bytes from the channel enable register, 2 bytes

from the input configuration register, and 1 byte from

the setup register, all MSB first. See the Global

Configuration Registers section for more details.

The Clear Alarm Register for All Channels command,

1001, clears the entire alarm register and resets the

fault counters for the internal TEMP sensor, the V

DD

monitor, and the AIN0–AIN7 channels. The address bits

in the command are ignored. See the Alarm Register

section for more details.

Write Current Data Register for Selected

Channel (Command Code 1010)

The Write Current Data Register for Selected Channel

command, 1010, writes to the addressed channel’s cur-

rent data register. This command sets an initial condi-

tion when using the averaging filter option (see the

Averaging section). This command can also be used for

testing the thresholds, fault counters, and alarm func-

tions (Figure 8). See Table 3 for channel addresses.

RESET (Command Code 0111)

The RESET command, 0111, resets the device. This

command returns the MAX1253/MAX1254 to their

power-on reset state, placing the device into shutdown

mode. The address bits in the command are ignored.

See the Power-Up/Reset Defaults Summary section for

more details.

Write Current Data Register for All

Channels (Command Code 1011)

Clear Channel Alarm for Selected Channel

(Command Code 1000)

The Clear Channel Alarm command, 1000, clears the

alarm bits in the alarm register and resets the fault

counter for the addressed channel. See the Alarm

Register section for more details. See Table 3 for chan-

nel addresses.

The Write Current Data Register for All Channels com-

mand, 1011, writes to the current data registers of all

channels sequentially, starting with the internal temper-

ature sensor, then the V

monitor, followed by chan-

DD

nels AIN0 to AIN7. The address bits are ignored. Use

this command for testing and setting initial conditions

when using the averaging filter option (see the

Averaging section).

CS

SCLK

DIN

C3 C2 C1 C0 A3 A2 A1 A0

D11 D10 D9 D8 D7 D6 D5 D4

D3 D2 D1 D0

HIGH-Z

DOUT

Figure 8. Serial Register Write Timing

______________________________________________________________________________________ 17

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

Write-Selected Channel Configuration

Registers (Command Code 1100)

Channel-Enable Register

The channel-enable register (Table 4) controls which

channels are converted while in automatic scan mode.

The register contents are ignored for manual conver-

sion commands. Each input channel has a correspond-

ing bit in the channel-enable register. A logic high

enables the corresponding analog input channel for

conversion, while a logic low disables it. In differential

configuration, the bits for odd channels are ignored. At

power-up and after a RESET command, the register

contents default to 111111111111b (all channels

enabled).

The Write-Selected Channel Configuration Register com-

mand, 1100, writes to the three channel configuration

registers for the addressed channel (see Table 3). The

first register to be written is the upper threshold (2 bytes),

followed by the lower threshold (2 bytes), ending with the

channel configuration register (1 byte), all MSB first.

Writing to the configuration registers resets the alarm reg-

ister bits and the fault counters for the addressed chan-

nel. See the Channel Registers section for more details.

Write Global Configuration Registers

(Command Code 1101)

Input Configuration Register

The input configuration register (Table 5) stores the

configuration code for each channel as a 3-bit per

channel-pair code (see Table 6), selecting from five

input signal configurations: single-ended unipolar volt-

age, single-ended temperature, differential unipolar

voltage, differential bipolar voltage, and differential

temperature. Table 5 shows the input configuration reg-

ister format, and Table 6 shows the 3-bit encoding for

channel configuration. At power-up and after a RESET

command, the register contents defaults to

000000000000b (all inputs single ended).

The Write Global Configuration Registers command,

1101, writes to three registers: the channel-enable reg-

ister (2 bytes), the input configuration register (2 bytes),

and the setup register (1 byte). The command address

bits are ignored. See the Global Configuration

Registers section for more details.

Global Configuration Registers

The global configuration registers consist of the chan-

nel-enable register, the input configuration register, and

the setup register. These registers hold configuration

data common to all channels.

Table 4. Channel-Enable Register Format

B11

(MSB)

B0

(LSB)

B10

B9

B8

B7

B6

B5

B4

B3

B2

B1

TEMP

VDD

AIN0

AIN1

AIN2

AIN3

AIN4

AIN5

AIN6

AIN7

Res

Table 5. Input Configuration Register Format

B11

B0

(LSB)

B10

B9

B8

B7

B6

B5

B4

B3

B2

B1

(MSB)

AIN0 and AIN1 configuration

AIN2 and AIN3 configuration

AIN4 and AIN5 configuration

AIN6 and AIN7 configuration

Table 6. Channel Configuration Coding (3 Bits/Channel Pair)

CODE

000

001

010

011

100

101

110

111

AIN0, AIN2, AIN4, AIN6 CONFIGURATION

Single-ended input (power-up state)

Single-ended input

AIN1, AIN3, AIN5, AIN7 CONFIGURATION

Single-ended input (power-up state)

Single-ended, external temperature sensor input

Single-ended input

Single-ended, external temperature sensor input

Differential unipolar encoded, positive input

Differential bipolar encoded, positive input

Differential external temperature sensor, positive input

Reserved

Single-ended, external temperature sensor input

Differential unipolar encoded, negative input

Differential bipolar encoded, negative input

Differential external temperature sensor, negative input

Reserved

18 ______________________________________________________________________________________

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

3) Sequence to the next-enabled channel until all

enabled channels have been converted.

Setup Register

The 8-bit setup register (Table 7) holds configuration

data common to all input channels. At power-up and

after a RESET command, this register defaults to

00000000b.

4) Wait the sample wait time, and enter internal refer-

ence power-down mode if this period is greater than

80µs.

5) Repeat the above steps.

Setup Register: Sample Wait Bits (B7, B6, B5)

These 3 bits in the setup register (Table 8) set the wait

time between conversion scans. The following are

examples of how the MAX1253/MAX1254 begin a sam-

ple sequence (see the Setup Register: Reference

Selection Bits (B1, B0) section).

Operating in reference mode 10 (internal reference for

all conversions, continuously powered up):

1) Convert the first-enabled channel.

2) Sequence to the next-enabled channel until all

enabled channels have been converted.

Operating in reference mode 00 (external reference for

voltage conversions, internal reference for temperature

conversions):

3) Wait the sample wait time.

4) Repeat the procedure.

1) Convert the first-enabled channel. If this channel is a

temperature measurement, power up the internal ref-

erence (this takes 20µs for each enabled tempera-

ture measurement in reference mode 00).

Use the sample wait feature to reduce supply current

when measuring slow-changing analog signals. This

power savings occurs when reference mode 00 or 01 is

used in combination with wait times longer than 80µs.

With reference mode 10 or wait times of less than 80µs,

the internal reference system remains powered up, mini-

mizing any power savings. See the Computing Data

Throughput section. Table 8 shows the B7, B6, B5 wait

time encoding.

2) Sequence to the next-enabled channel until all chan-

nels have been converted.

3) Wait the sample wait period.

4) Repeat the procedure.

Operating in reference mode 01 (internal reference for all

conversions, can be powered down between scans):

Setup Register: Interrupt Control (B4, B3)

Bits B3 and B4 in the setup register configure INT and

how it responds to an alarm event (see the Alarm

Register section). Table 9 shows the available INT

options.

1) Power up the internal reference, if powered down

(this takes 40µs).

2) Convert the first-enabled channel, starting with the

internal temperature sensor, if enabled.

Table 7. Setup Register Format

B7 (MSB)

B6

B5

B4

B3

B2

B1

B0 (LSB)

Interrupt

active

Interrupt

polarity

Scan

mode

Reference

source B1

Reference

source B2

Sample wait bits

Table 8. Wait Time Encoding

Table 9. Interrupt Control

B7, B6, B5

000

WAIT TIME (ms)

BIT

BIT FUNCTION

STATE

INT OPERATION

0

001

0.080

0.395

1.310

4.970

19.600

78.200

312.000

1

0

Driven high or low at all times

Output

driver type

010

B4

B3

High-Z when inactive, driven (high

or low) when active

011

100

1

0

Active = high, inactive = low or high-Z

Active = low, inactive = high or high-Z

Output

polarity

101

110

111

______________________________________________________________________________________ 19

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

Setup Register: Scan Mode Bit (B2)

The scan mode bit selects between automatic scan-

ning and manual conversion mode.

Setup Register: Reference Selection Bits (B1, B0)

The MAX1253/MAX1254 can be used with an internal

or external reference. Select between internal and

external reference modes through bits B1 and B0 of the

setup register (see Table 10).

When set (B2 = 1), the MAX1253/MAX1254 enter auto-

matic scanning mode and convert every enabled chan-

nel starting with the internal temperature sensor,

Alarm Register

followed by the V

AIN0 to AIN7.

monitor, then sequencing through

DD

The alarm register (Table 11) holds the current alarm sta-

tus for all of the monitored signals. This 24-bit register

can only be read and cleared. The alarm register has 2

bits for each external input channel, 2 for the onboard

After converting all the enabled channels, the

MAX1253/MAX1254 enter a wait state set by the sam-

ple wait bits in the setup register. After completing the

sample wait time, the scan cycle repeats.

temperature sensor, and 2 for the V

monitor (see

DD

Table 12). At power-up, these bits are logic low, indicat-

ing no alarms at any input. When any bit in the alarm reg-

ister is set, INT becomes active and remains active until

all alarm bits are cleared. After a fault counter exceeds

the set threshold, the alarm register bits for that particular

channel are updated to indicate an alarm.

When B2 = 0, the MAX1253/MAX1254 are in manual

mode and convert only the selected channel after

receiving a Manually Triggered Conversion command

(see the Manually Triggered Conversion (Command

Code 0000) section). Whether in automatic scanning

mode or manual mode, a Read Current Data Register

for Selected Channel command outputs the last-com-

pleted conversion result for the addressed channel at

DOUT.

To clear the interrupt, reset the active alarm bit with the

Clear Alarm Register command, Clear Channel Alarm

command, a RESET command, or by writing a new

configuration to the faulting channel. The alarm register

defaults to 000000 hex.

Table 11 illustrates how the alarm register stores the

information on which channel a fault has occurred. The

alarm code for each bit pair is shown in Table 12.

Table 10. Reference Selection

B1 B0

REFERENCE MODE

Channel Registers

Voltage measurements use external reference,

while temperature measurements use the internal

reference. A 20µs reference startup delay is

added prior to each temperature measurement

in this mode. This is the default mode after

power-up and after a software RESET.

Each channel (internal temperature sensor, V

moni-

DD

tor, and AIN0 to AIN7) has registers to hold the conver-

sion result (current data register) and channel-specific

configuration data. The channel-specific configuration

registers include: the upper threshold register, the

lower threshold register, and the channel configuration

register. In differential mode, only the registers for the

even channel of the differential input pair are used. The

channel-specific configuration registers for the odd

channel of a differential channel pair are ignored.

0

1

All measurements use the internal reference. A

40µs reference startup delay is added prior to

starting the scanning of enabled channels,

allowing the internal reference to stabilize.

Note:

For sample wait times less than 80µs, the

reference is continuously powered when in

automatic scan mode.

Table 12. Alarm Register Coding

(2 Bits/Channel)

All measurements use the internal reference. By

selecting this mode, the reference is powered up

immediately when CS goes high after writing this

configuration. Once the reference system is

powered up, no further delay is added.

CODE

00

DESCRIPTION

No alarm (power-up state)

1

0

1

01

Input is below lower threshold

Input is above upper threshold

Reserved

10

Reserved.

00

Table 11. Alarm Register Format

B23/B22 B21/B20 B19/B18 B17/B16 B15/B14 B13/B12 B11/B10

TEMP AIN0 AIN1 AIN2 AIN3 AIN4

B9/B8

B7/B6

B5/B4

B3/B2

B1/B0

V

AIN5

AIN6

AIN7

Res

DD

20 ______________________________________________________________________________________

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

Table 13. Channel Configuration Register Format

B7 (MSB)

B6

B5

B4

B3

B2

B1

B0 (LSB)

Fault B3

Fault B2

Fault B1

Fault B0

Ave B3

Ave B2

Ave B1

Ave B0

fault occurs and the next scan finds the input within the

normal range defined by the thresholds, the fault

counter resets. If the next counter finds the input signal

outside the opposite threshold, rather than the previous

one, the fault counter also resets. The fault counter

increments only when counting consecutive faults

exceeding the same threshold (Figure 4).

Table 14. Conversion Average Encoding

CODE

0000

0001

0010

0011

0100

0101

0110

0111

1000

1001

1010

1011

1100

1101

1110

1111

N

1, no averaging

2

4

8

Averaging

The averaging calculated by the data-acquisition algo-

rithm of the MAX1253/MAX1254 improves the input sig-

nal-to-noise ratio (SNR) by reducing the signal

bandwidth digitally. The formula below describes the

filter implemented in the MAX1253/MAX1254:

16

32

64

128

256

current value = [(N - 1) / N] x past value +

[(present value) / N]

512

1024

2048

Reserved

where N = number of samples indicated in Table 14.

The averaging bits (B3–B0) in the channel configuration

register can set the N factor to any value in Table 14.

The output of the filter-running algorithm is continuously

available in the current data register. The starting value

used by the algorithm is the initial state of the current

data register. The current data register is reset to mid-

scale (800 hex) at power-up or after a RESET com-

mand, but it can be loaded with a more appropriate

initial value to improve the filter settling time.

Channel Configuration Register

Each channel has a channel configuration register

(Table 13) defining the number of consecutive faults to

be detected before setting the alarm bits and generat-

ing an interrupt, as well as controlling the digital averag-

ing. At power-up and after a RESET command, the

register defaults to 00 hex (no averaging, alarm on first

fault).

At power-up or after a RESET command, the B3–B0

bits of the channel configuration register are set to 0

hex, corresponding to a number of averaged N = 1, no

averaging. See Table 13 and the Write-Selected

Channel Configuration Registers section for program-

ming details. See Table 14 for N encoding.

Fault Bits

The value stored in the fault bits (B7–B4) in the channel

configuration register sets the number of faults that

must occur for that channel before generating an inter-

rupt. Encoding of the fault bits is straight binary with

valves 0 to 15. A fault occurs in a channel when the

value in its current data register is outside the range

defined by the channel’s upper and lower threshold

registers. For example, if the number of faults set by the

fault bits is N, an interrupt is generated when the num-

ber of consecutive faults (see note below) reach (N +

1). The fault bits default to 0 hex at power-up.

As in all digital filters, truncation can be a cause of sig-

nificant errors. In the MAX1253/MAX1254, 24 bits of

precision are maintained in the digital averaging func-

tion, maintaining a worst-case truncation error of well

below an LSB. The worst-case truncation error in the

MAX1253/MAX1254 is given by the following:

N-1

4096

worst-case truncation error =

LSBs

where N = number of conversions averaged.

Therefore, the worst truncation error when averaging

256 samples is 0.0623 LSBs.

Note: Consecutive faults are those happening in con-

secutive conversion scans for the same channel. If a

______________________________________________________________________________________ 21

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

nel configuration register, the alarm bits for that particular

channel are updated to indicate an alarm. When any bit in

the alarm register is set, the INT output becomes active,

and stays active until all alarm bits are cleared. See the

Alarm Register section for more information.

Upper Threshold Register

A conversion result greater than the value stored in the

upper threshold register results in a fault, increasing

the internal fault counter by one. When the fault count

exceeds the value stored in fault bits B7–B4 of the

channel configuration register, the channel’s alarm bits

in the alarm register are set, resulting in an interrupt on

INT.

Servicing Interrupts at INT

After detecting an interrupt on INT, the µC’s interrupt

routine should first read the alarm register to find the

source of the alarm and reset the alarm bits by using

any of the methods described in the Alarm Register

section. Then it can continue with any other action

required by the application to react to the alarm.

The upper threshold register data format must be the

same as the input channel. When the input channel is

configured for single-ended or differential unipolar volt-

age measurements, data stored in the upper threshold

register is interpreted as straight binary. For input chan-

nels configured for temperature measurements or as

differential bipolar voltage inputs, the upper threshold

register data is interpreted as two’s complement. Load

the register with FFF hex to disable upper threshold

faults in unipolar mode, and 7FF hex in temperature or

bipolar mode. The power-up/reset default is FFF hex.

See the Command Word section on how to read/write

to the upper threshold registers.

Note: Multiple alarm conditions can be present. The

INT remains active until all alarm conditions have been

cleared.

Performing Conversions

At power-up or after a RESET command, the

MAX1253/MAX1254 default to shutdown mode with all

channels enabled, set for single-ended voltage mea-

surements, and with the scan mode set to manual. Start

a conversion by issuing a manually triggered conver-

sion command with the address bits of the channel

selected (see the Manual Conversion section for more

details) or by setting automatic scan mode. To place

the MAX1253/MAX1254 in automatic scan mode, set

scan mode bit B2 in the setup register to logic 1.

Lower Threshold Register

Conversion results lower than the value stored in the

lower threshold register increment the internal fault

counter. Considerations about channel configuration

register fault bits B7–B4, INT interrupts, and data for-

mat are the same as for the upper threshold register.

Set the register to 000 hex to disable lower threshold

faults in unipolar mode, or to 800 hex in temperature or

bipolar mode. The power-up/reset default is 000 hex.

See the Command Word section on how to read/write

to the lower threshold registers.

In automatic scan mode, the MAX1253/MAX1254 con-

vert all enabled channels starting with the internal tem-

perature sensor, followed by the V

monitor, then by

DD

AIN0 to AIN7. As the scan sequence progresses, the

analog inputs are converted and the resulting values

are stored for each channel into its current data regis-

ter. Once the scan cycle completes, the MAX1253/

MAX1254 wait a period determined by the sample wait

bits (B7, B6, B5) in the setup register and then repeat

the scan cycle.

Current Data Registers

The current data register holds the last conversion

result or the digitally averaged result, when enabled

(see the Averaging section). The current data registers

default to 800 hex at power-up/reset and can be read

from and written to through the serial interface. See the

Command Word section on how to read/write to the

current data registers.

After configuring the MAX1253/MAX1254 with automat-

ic scan mode enabled, the devices do not require any

intervention from the system µC until an alarm is trig-

gered. All conversion and monitoring functions can

continue running indefinitely.

INT Interrupt Output

INT provides an indication that an alarm has occurred

in the system. It can be programmed (see Table 9) to

operate as a push-pull digital output or as an open-

drain output (requiring either a pullup or a pulldown

resistor) for wired-OR interrupt lines. Bits B3 and B4 in

the setup register configure INT and determine its

response to an alarm event.

Manual Conversion

In manual mode (scan mode bit in the setup register

set to zero, the default after power-up/reset), the

MAX1253/MAX1254 convert individual channels with

the Manually Triggered Conversion command.

Assuming that, either by power-up/RESET defaults or

by previous initialization, the channel to be addressed

is both enabled and configured for the type of signal to

be acquired (voltage/temperature, single ended/differ-

When an internal fault counter exceeds the threshold

stored in the fault bits (B7–B4) of the corresponding chan-

22 ______________________________________________________________________________________

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

ential, or unipolar/bipolar), carry out the following steps

to execute a manual conversion. See Figure 9 for man-

ual conversion timing:

V

value can be calculated from the digitized data

DD

with the following equation:

V

4096





REF

1) Disable autoscan (set up register scan mode bit to

zero), if necessary.

V

DD

= 2 x (current_data_register_content) x









2) Pull CS low.

The reference voltage must be larger than 1/2V

for

DD

3) Initiate a conversion by issuing a Manually Triggered

Conversion command (0000, followed by the

address bits of the channel to be converted).

the operation to work properly. V

10.6µs (typ) per measurement.

monitoring requires

DD

Temperature Measurement

The MAX1253/MAX1254 perform temperature measure-

ment by measuring the voltage across a diode-con-

nected transistor at two different current levels. The

following equation illustrates the algorithm used for

temperature calculations:

4) Pull CS high to start the conversion.

5) Maintain a logic high on CS to allow for reference

power-up (if the reference mode requires it) and

conversion time.

6) Pull CS low.

7) Issue a Read Current Data Register for Selected-

Channel command (0010, followed by the same

address of the channel in the Manually Triggered

Conversion command).

q

k

temperature = (V

- V ) x

LOW

HIGH

I





High

n x ln









LOW

Voltage Measurements

Every voltage measurement (internal V

or external

DD

input channel) requires 10.6µs to complete. If the inter-

nal reference needs to power up (reference mode =

01), an additional 40µs is required every time the

MAX1253/MAX1254 come out of automatic shutdown

mode after a sample wait period greater than 80µs.

where:

V

(I

= sensor-diode voltage with high current flowing

HIGH

)

V

(I

= sensor-diode voltage with low current flowing

LOW

)

LOW

Monitoring V

q = charge of electron = 1.602 ✕ 10^-19coulombs

k = Boltzman constant = 1.38 ✕ 10^-23J/K

n = ideality factor (slightly greater than 1)

DD

This internal acquisition channel samples and converts

the supply voltage, V

.

DD

t

PU+CONV

CS

SCLK

C3

C2 C1 C0 A3 A2 A1 A0

C3 C2 C1 C0 A3 A2 A1 A0

DIN

DOUT

Figure 9. Manual Conversion Timing Without Reading Data

______________________________________________________________________________________ 23

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

The temperature measurement process is fully auto-

mated in the MAX1253/MAX1254. All steps are

sequenced and executed by the MAX1253/MAX1254

each time an input channel (or an input channel pair)

configured for temperature measurement is scanned.

the MAX1253/MAX1254 by issuing a command to read

a specific channel with the Read Current Data Register

for Selected Channel command. Read all current data

registers at once with the Read Current Data Registers

for All Channels command.

The resulting 12-bit, two’s complement number repre-

sents the sensor temperature in degrees Celsius, with

1 LSB = +0.125°C.

The MAX1253/MAX1254 support both single-ended

and differential temperature measurements.

For more complex applications, the monitoring and

interrupt generation features of the MAX1253/MAX1254

require a second step of initialization. Each enabled

channel to be monitored requires configuration using a

Write Configuration Register for Selected Channel com-

mand. Each command is a 5-byte write that sets the

upper and lower fault thresholds, the number of faults for

an alarm before an interrupt is generated, and an aver-

age algorithm parameter if the application requires input

signal filtering.

Applications Information

Setting Up the

MAX1253/MAX1254 Subsystem

The MAX1253/MAX1254 are autonomous subsystems,

requiring only initialization to scan, convert, and monitor

the voltage signals or the temperature sensors con-

nected to their input channels.

Applications can read the current data registers and

respond to interrupts signaled by the INT output (see

the Servicing Interrupts at INT section).

All the MAX1253/MAX1254 registers can be verified by

reading back written data, including the configuration

registers. This feature is useful for development and

testing (see Table 2).

For simple applications, using any number of the input

channels and any combination of voltage/temperature

and unipolar/differential, with no interrupt generation

required, use the following intitialization procedure:

Power-Up/Reset Defaults Summary

• Issue a Write Global Configuration Registers com-

mand. This is a single, 5-byte write operation that con-

figures the input channels, enables the channels to be

used, sets the sample wait time between scans, con-

figures the interrupt output INT, selects the reference

mode, and starts the automatic scan mode. See the

Write Global Configuration Registers Command sec-

tion, Table 2, and Tables 5–10.

Setup Register Power-Up/Reset Defaults

At initial power-up or after a RESET command, the

setup register resets to 00 hex. Consequently, the

MAX1253/MAX1254 are configured as follows:

• Sample wait time is 0µs.

• INT output is open drain and outputs an active-low

signal to signify an alarm.

Immediately after the global configuration register is

loaded, the MAX1253/MAX1254 begin to update the

current data registers. Acquire conversion data from

• Manual conversion mode.

• External reference for voltage measurements.

Table 15. Power-Up/Reset Defaults Summary

REGISTER

BIT RANGE

B0 to B7

B0 to B11

B0 to B23

B0 to B7

B0 to B9

POWER-UP/RESET STATE

COMMENTS

See Setup Register Power-Up/Reset Defaults

All channels (int/ext) enabled

All single-ended voltage inputs

No alarms set

Setup

All 0s

All 1s

All 0s

All 1s

All 0s

200hex

Channel enable

Input configuration

Alarm register

Channel configuration

Upper threshold

Lower threshold

Current data registers

Faults = 0, no averaging

All upper thresholds max range

All lower thresholds min range

Set at midrange

24 ______________________________________________________________________________________

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

Channel-Enable Register Power-Up/Reset Defaults

At power-on or after a RESET command, the channel-

enable register resets to FF hex, enabling all channels:

ple wait period (if sample wait time > 80µs), and no

power-up time in reference mode 10.

The sampling period is calculated as follows:

the internal temperature sensor, the V

monitor, and

DD

t

sw

= (t ) + (N )t

+ (N )t

+ t

pu

v conv[volt]

t conv[temp] wait

AIN0–AIN7.

where:

Input Configuration Register

Power-Up/Reset Defaults

At power-on or after a RESET command, the input con-

figuration register resets to 00 hex, configuring

AIN0–AIN7 for single-ended voltage measurement.

t

= all channels scan sampling period

= reference power-up time

sw

pu

= voltage-configured channel conversion time

conv[volt]

N = number of voltage-configured channels

v

Alarm Register Power-Up/Reset Defaults

At power-on or after a RESET command, the alarm reg-

ister is reset to 000000 hex, indicating that no alarm

condition exists.

t

= temperature-configured channel conver-

conv[temp]

sion time

N = number of temperature-configured channels

t

= sample wait time

wait

Current Data Register Power-Up/Reset Defaults

At power-on or after a RESET command, each chan-

nel’s current data register is reset to 800 hex.

The terms in the above equation are determined as

shown above by the number of enabled channels, the

input channel configuration (voltage vs. temperature),

the sample wait time, and the reference mode. The fol-

lowing calculation shows a numeric example:

Upper Threshold Register Power-Up/Reset Defaults

At power-on or after a RESET command, each chan-

nel's upper threshold register is reset to FFF hex. This

state effectively disables the upper threshold.

t

= 40µs + 8 x 10.6µs + 2 x 46µs + 395µs = 611.8µs

sw

• 40µs is the time required for the reference to power-

up (reference mode = 00) every time the

MAX1253/MAX1254 come out of automatic shut-

down mode after a sample wait period.

Lower Threshold Register Power-Up/Reset Defaults

At power-on or after a RESET command, each chan-

nel's lower threshold register is reset to 000 hex. This

state effectively disables the lower threshold.

• 8 x 10.6µs is the time required for seven channels

configured for voltage measurement and the V

monitor.

DD

Channel Configuration Register

Power-Up/Reset Defaults

At power-on or after a RESET command, each chan-

nel's configuration register is reset to 000 hex, which

configures the fault bits to cause an alarm to occur on

the first overrange or underrange condition and dis-

ables averaging.

• 2 x 46µs is the time required for temperature mea-

surement (46µs for each temperature measurement

(internal or external)).

• 395µs is the sample wait time, set by bits B5, B6, B7

of the setup register (see Tables 7 and 8).

The MAX1253/MAX1254 use an internal clock for all

conversions. The serial interface clock does not affect

conversion time.

Computing Data Throughput

The MAX1253/MAX1254 throughput rate depends on

the number of enabled channels, their configuration

(temperature or voltage), and the reference mode.

Voltage measurements require 10.6µs (typ) to com-

plete, and temperature measurements require 46µs.

Performing eight single-ended remote channels tem-

perature measurements, an internal temperature mea-

surement, and an internal V

measurement with a

DD

sample wait time of zero results in an average conver-

sion rate of 24ksps or 2.4ksps per channel.

Channel pairs configured for differential measurements

count as only one for throughput computation.

Performing eight single-ended voltage measurements, an

The reference system takes 20µs to power up in refer-

ence mode 00 prior to each temperature measurement,

40µs to power up in reference mode 01 after each sam-

internal temperature measurement, and an internal V

DD

measurement with sample wait time of zero results in an

average conversion rate of 70ksps or 7ksps per channel.

______________________________________________________________________________________ 25

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

Single-Ended Temperature Measurement

Connect the anode of a diode-connected transistor to

the input channel and the cathode to ground. Choose

ground connections for sensors away from high-current

return paths to avoid the introduction of errors caused by

voltage drops in the board/system ground, which is the

main drawback for single-ended measurements.

Practical options for better accuracy are the use of a

star-configured subsystem ground or a signal ground

plane; to isolate the anode sensor connection trace away

from board and system noise sources; or to shield it with

ground lines and ground planes (when available) to pre-

vent accuracy degradation in the temperature measure-

ments caused by magnetic/electric noise induction.

Automatic Reference Shutdown

The MAX1253/MAX1254 enter an automatic shutdown

mode when in reference mode 00 or when the sample

wait is greater than 80µs in reference mode 01. Using

either of these reference modes and a sample wait

period as long as the application allows results in the

lowest power consumption.

Temperature Measurement

The MAX1253/MAX1254 support both single-ended

and differential temperature measurements. The design

decision between the two types of measurements

depends on the desired level of accuracy and on type

and/or number of temperature sensors. The superior

common-mode rejection and lower noise of the differ-

ential mode reduces measurement errors and provides

higher accuracy, while single-ended measurements

require a lower number of connections, resulting in a

simpler implementation and a higher number of moni-

tored points for each MAX1253/MAX1254.

Configure the MAX1253/MAX1254 input used for single-

ended temperature measurement in the input configura-

tion register (see Tables 9 and 10) and enable the analog

input in the channel-enable register (see Table 4).

Remote Temperature Sensor Selection

Temperature-sensing accuracy depends on having a

good-quality, diode-connected, small-signal transistor

as a sensor. Accuracy has been experimentally verified

for 2N3904-type devices. The transistor must be a

small-signal type with low base resistance. Tight speci-

fications for forward current gain (+50 to +150, for

example) indicate that the manufacturer has good

process controls and that the devices have consistent

Differential Temperature Measurement

Connect the anode of a diode-connected transistor to

the even input channel and the cathode to the odd

input channel of an input pair configured for differential

temperature measurement (AIN0/AIN1, AIN2/AIN3,

AIN4/AIN5, or AIN6/AIN7). Run the two sensor connec-

tion lines parallel to each other with minimum spacing.

This improves temperature measurement accuracy by

minimizing the differential noise between the two lines,

since they have equal exposure to most sources of

noise. For further improved noise rejection, shield the

two sensor connections by running them between

ground planes, when available.

V

characteristics. CPU on-board sensors and other

BE

ICs’ on-board temperature-sensing devices can also

be used (see Table 16 for recommended devices).

Configure the MAX1253/MAX1254 inputs for differential

temperature measurement in the input configuration

register (see Tables 9 and 10) and enable the even

channel number in the channel enable register (see

Table 4).

OUTPUT CODE

FULL-SCALE

11....111

11....110

11....101

TRANSITION

Table 16. Remote Sensor Transistor

Manufacturers

FS = V

ZS = 0

REF

MANUFACTURER

MODEL NUMBER

V

REF

Central Semiconductor (USA)

CMPT3904

1 LSB =

00....011

00....010

00....001

00....000

4096

Fairchild Semiconductors (USA) MMBT3904

Motorola (USA)

MMBT3904

SST3904

Rohm Semiconductor (Japan)

Siemens (Germany)

Zetex (England)

0

1

2

3

FS

FS = 3/2 LSB

INPUT VOLTAGE (LSB)

SMB3904

FMMT3904CT-ND

MMBT3904

Diodes Inc.

Figure 10. Unipolar Transfer Function, Full Scale (FS) = V

REF

26 ______________________________________________________________________________________

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

OUTPUT CODE

FS =

V

REF

2

011....111

011....110

000....010

011....110

ZS = 0

-V

REF

-FS =

2

V

000....010

REF

1 LSB =

000....001

000....000

111....111

111....110

111....101

000....001

000....000

111....111

111....110

111....101

4096

100....001

100....000

100....001

100....000

0

-256°C

+255.875°C

-FS

+FS - 1 LSB

TEMPERATURE °C

INPUT VOLTAGE (LSB)

Figure 12. Temperature Transfer Function

Figure 11. Bipolar Transfer Function, Full Scale ( FS) =

V /2

REF

noisy, connect a 10Ω resistor in series with the supply

Transfer Function

Figure 10 shows the nominal transfer function for single-

ended or differential unipolar configured inputs, Figure

11 illustrates the transfer function for differential bipolar

conversions, and Figure 12 shows temperature conver-

sions. Code transitions occur halfway between succes-

sive-integer LSB values. Output coding is binary, with

1 LSB = 610µV (MAX1253) or 1mV (MAX1254) for unipo-

lar and bipolar operation, and 1 LSB = +0.125°C

(MAX1253/MAX1254) for temperature measurements.

to improve power-supply filtering.

Definitions

Integral Nonlinearity

Integral nonlinearity is the deviation of the values on the

actual transfer function from a straight line. This straight

line can be either a best-straight-line fit or a line drawn

between the end points of the transfer function, once off-

set and gain errors have been corrected. The static lineari-

ty parameters for the MAX1253/MAX1254 are measured

using the end-point-fit method. INL is specified as the

maximum deviation in LSBs.

For unipolar operation, the 0 code level transition is at

[1/2(V

/ 4096)].

REF

The FFF hex level transition is at [4094.5 (V

/ 4096)].

REF

1 LSB = V

/ 4096.

Differential Nonlinearity (DNL)

Differential nonlinearity is the difference between an

actual step width and the ideal value of 1 LSB. A DNL

error specification of less than 1 LSB guarantees no

missing codes and a monotonic transfer function.

REF

Layout, Grounding, and Bypassing

For best performance, use PC boards. Do not use wire-

wrap boards. Board layout should ensure that digital

and analog signal lines are separated from each other.

Do not run analog and digital (especially clock) signals

parallel to one another or run digital lines underneath

the MAX1253/MAX1254 package. High-frequency

Offset Error

The offset error is the difference between the ideal and

the actual analog input value at the first transition of the

ADC, usually from digital code 0 to code 1 for straight

binary output. For the MAX1253/MAX1254, the transi-

tion between code 0 and code 1 should occur at an

input voltage of 1/2 LSB, or 305µV for the MAX1253

and 500µV for the MAX1254.

noise in the V

power supply can affect the

DD

MAX1253/MAX1254 performance. Bypass the V

sup-

DD

ply with a 0.1µF capacitor from V

to GND, close to

DD

the V

pin. Minimize capacitor lead lengths for best

DD

supply-noise rejection. If the power supply is very

______________________________________________________________________________________ 27

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

There are other noise sources besides quantization

noise, including thermal noise, reference noise, clock

jitter, etc. Therefore, SINAD is calculated by taking the

ratio of the full-scale signal to the RMS noise, which

includes all spectral components minus the fundamen-

tal and the first five harmonics.

Gain Error

The gain error is the difference between the ideal and

actual value of the analog input difference between the

first and last transitions of the ADC output. The first

transition is from digital code 0 to code 1, and the last

from code (2^N-2) to code (2^N-1), where N = number of

ADC bits for straight binary output code. For the

MAX1253/MAX1254, the ideal difference in the input

voltage between code transitions 0 to 1 and code tran-

sitions 4094 to 4095 is 4094 x LSB. For the MAX1253,

this is 2.5V - 2 x LSB = 2.498780V, and for the

MAX1254, this is 4.096V - 2 x LSB = 4.094V. Gain error

is a DC specification, usually normalized to the FS ideal

analog value and given in percent of FSR or ppm.

Total Harmonic Distortion (THD)

Total harmonic distortion (THD) is the ratio of the RMS

sum of the first five harmonics of the input signal to the

fundamental itself. This is expressed as:









2

V

+ V

5

(

)

2

3

4

THD = 20 x log

V

1

Signal-to-Noise Ratio

For a waveform perfectly reconstructed from digital

samples, signal-to-noise ratio (SNR) is the ratio of the

full-scale analog input (RMS value) to the RMS quantiza-

tion error (residual error). The ideal theoretical minimum

analog-to-digital noise is caused by quantization error

only, results directly from the ADC’s resolution (N bits),

and can be calculated with the following equation:

where V is the fundamental RMS value, and V

1

2

through V are the RMS values of the 2nd- through 5th-

5

order harmonics, respectively.

Power-Supply Rejection

Power-supply rejection is the ratio between the change

in the ADC full-scale output to the change in power-

supply voltage when the power-supply voltage is varied

from its nominal value. It is specified in V/V or µV/V.

SNR = (6.02 x N + 1.76)dB

Signal-to-Noise Plus Distortion

Signal-to-noise plus distortion (SINAD) is the ratio of the

fundamental input frequency’s RMS amplitude to the

RMS equivalent of all other ADC output signals:

SINAD (dB) = 20 x log (Signal

/ Noise

)

RMS

28 ______________________________________________________________________________________

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V Monitor

DD

Typical Operating Circuit

POWER SUPPLY

µC

+V

-5V

+5V

+3V

V

DD

V

REF

REFERENCE

GLOBAL REGISTERS

TEMP

SENSOR

INT

SPI

INTERFACE

SPI I/F

AIN0

AIN1

AIN2

AIN3

AIN4

AIN5

AIN6

AIN7

ADC

DIGITAL BLOCK

48V

MUX

MAX1253

MAX1254

CHANNEL REGISTERS

GND

REMOTE TEMP

Chip Information

TRANSISTOR COUNT: 89,473

PROCESS: 0.6µm BiCMOS

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are

implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 29

Printed USA

is a registered trademark of Maxim Integrated Products.

型号:	MAX1254AEUE
是否无铅：	含铅
是否Rohs认证：	不符合
生命周期：	Obsolete
IHS 制造商：	MAXIM INTEGRATED PRODUCTS INC
零件包装代码：	TSSOP
包装说明：	TSSOP-16
针数：	16
Reach Compliance Code：	not_compliant
ECCN代码：	EAR99
HTS代码：	8542.39.00.01
风险等级：	5.78
Is Samacsys：	N
其他特性：	ONE OF THE INTERNAL CHANNEL MONITORS THE INTERNAL IC TEMPERATURE
可调阈值：	YES
模拟集成电路 - 其他类型：	POWER SUPPLY SUPPORT CIRCUIT
JESD-30 代码：	R-PDSO-G16
JESD-609代码：	e0
长度：	5 mm
湿度敏感等级：	1
信道数量：	9
功能数量：	1
端子数量：	16
最高工作温度：	85 °C
最低工作温度：	-40 °C
封装主体材料：	PLASTIC/EPOXY
封装代码：	TSSOP
封装形状：	RECTANGULAR
封装形式：	SMALL OUTLINE, THIN PROFILE, SHRINK PITCH
峰值回流温度（摄氏度）：	240
认证状态：	Not Qualified
座面最大高度：	1.1 mm
最大供电电压 (Vsup)：	5.5 V
最小供电电压 (Vsup)：	4.5 V
标称供电电压 (Vsup)：	5 V
表面贴装：	YES
技术：	BICMOS
温度等级：	INDUSTRIAL
端子面层：	Tin/Lead (Sn85Pb15)
端子形式：	GULL WING
端子节距：	0.65 mm
端子位置：	DUAL
处于峰值回流温度下的最长时间：	20
宽度：	4.4 mm
Base Number Matches：	1

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