MAX8677C各脚功能电路原理芯片引脚定义引脚图及功能IC贸易商-中国IC网-芯三七

19-0781; Rev 0; 4/07

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

MAX867C

General Description

Features

The MAX8677C is an integrated 1-cell Li+ charger and

Smart Power Selector™ with dual (DC and USB) power

inputs. It can operate with either separate inputs for

USB and AC adapter power*, or from a single input that

accepts both. All power switches for charging and

switching the load between battery and external power

are included on-chip. No external MOSFETs are

required.

o Complete Charger and Smart Power Selector

o No External MOSFETs Required

o Common or Separate USB and Adapter Inputs

o System Operates with Discharged or No Battery

o Automatic Adapter/USB/Battery Switchover

o Load Peaks Over Adapter Rating Are Supported

The MAX8677C features a Smart Power Selector to

make the best use of limited USB or adapter power.

The battery charge current and input current limit are

independently set up to 1.5A and 2A, respectively.

Input power not used by the system charges the bat-

tery. USB input current can be set to 100mA or 500mA.

Automatic input selection switches the system load

from battery to external power.

by Battery

o Input Overvoltage Protection to 16V

o 40mΩ System-to-Battery Switch

o Thermal Regulation Prevents Overheating

o PREQ, CHG, DOK, UOK, and FLT Indicators

o 4.35V (typ) SYS Regulation Voltage

Other features include overvoltage protection (OVP),

charge status and fault outputs, power-OK monitors,

charge timer, and battery thermistor monitor.

Additionally, on-chip thermal limiting reduces the battery

charge rate to prevent overheating. The MAX8677C is

available in a 4mm x 4mm, 24-pin TQFN-EP package.

Ordering Information

PIN-

PACKAGE

PKG

CODE

PART

TEMP RANGE

24 TQFN-EP**

(4mm x 4mm)

MAX8677CETG+ -40°C to +85°C

T2444-4

Applications

+Denotes a lead-free package.

**EP = Exposed paddle.

PDAs, Palmtops, and Wireless Handhelds

Smart Cell Phones

Portable Media/MP3 Players

GPS Navigation

Pin Configuration

Digital Cameras

18 17 16 15 14 13

Typical Operating Circuit

CHG 19

SYS 20

SYS 21

DOK 22

UOK 23

FLT 24

12 THM

11 ISET

10 CT

AC

ADAPTER

SYS

LOAD

DC

Q1

MAX8677C

CHARGE

9

8

7

GND

VL

CURRENT

SYSTEM

LOAD

PSET

USB

Q2

Q3

BAT

BATTERY

1

2

3

4

5

6

CHARGE AND

SYS LOAD

SWITCH

TQFN

(4mm x 4mm x 0.8mm)

GND

MAX8677C

*Protected by US Patent #6,507,172.

Smart Power Selector 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.

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

ABSOLUTE MAXIMUM RATINGS

DC, PEN1 to GND .................................................-0.3V to +16V

USB to GND .............................................................-0.3V to +9V

VL to GND ................................................................-0.3V to +4V

BAT, SYS, CEN, USUS, PEN2, TSET to GND...........-0.3V to +6V

THM, PSET, ISET, CT to GND .........................-0.3V to VL + 0.3V

PREQ, CHG, DOK, UOK, FLT to GND .....................-0.3V to +6V

EP (exposed paddle) to GND ...............................-0.3V to +0.3V

USB Continuous Current (total in 2 pins) .......................2.0A

RMS

BAT Continuous Current (total in 2 pins)........................2.4A

Continuous Power Dissipation (T = +70°C)

A

(derate 27.8mW/°C above +70°C)........................... 2222mW

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

Junction Temperature Range............................-40°C to +125°C

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

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

DC Continuous Current (total in 2 pins) .........................2.4A

SYS Continuous Current (total in 2 pins)........................2.4A

RMS

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.

MAX867C

ELECTRICAL CHARACTERISTICS

(V

= 5V, THM = CEN = USUS = GND, V

= 4V, V

= V

= 5V, USB, TSET, PREQ, CHG, DOK, UOK, FLT are unconnected,

DC

BAT

PEN1

PEN2

T = -40°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.) (Note 1)

A

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

DC-TO-SYS PREREGULATOR

DC Operating Range

4.1

6.6

14

V

DC Standoff Voltage

V

= V

= 0V

BAT

SYS

DOK

DC Undervoltage Threshold

DC Overvoltage Threshold

When V

goes low, V

rising, 500mV typical hysteresis

3.95

6.8

4.0

6.9

1

4.05

7.0

2

DC

goes high, V rising, 360mV typical hysteresis

DC

I

= I

= 0mA, V

= 0V

= 5V

SYS

BAT

CEN

DC Supply Current

mA

= 0mA, V

0.8

195

0.2

1.5

333

0.35

DC Shutdown Current

V

= V

= USUS = 5V, V = 0V

PEN1

µA

DC

CEN

DC-to-SYS On-Resistance

I

= 400mA, V

= 5V

CEN

Ω

SYS

When SYS regulation and charging stops, V

150mV hysteresis

falling,

DC

DC-to-BAT Dropout Voltage

10

50

90

mV

mA

R

= 1.5kΩ

1800

900

2000

1000

475

2200

1100

500

PSET

= 3kΩ

= 6.3kΩ

450

DC Current Limit

(See Table 2 for Input Source

Control)

V

= 6V, V

= +25°C

= 5V,

SYS

DC

V

= 0V, V

= 5V

PEN2

PEN1

T

A

450

80

475

95

500

100

(500mA USB mode)

V

= 0V, V = 0V

PEN1

PEN2

(100mA USB mode)

PSET Resistance Range

SYS Regulation Voltage

1.5

6.3

kΩ

V

= 6V, I

= 1mA to 1.75A, V = 5V

CEN

4.29

4.35

1.5

50

4.40

DC

SYS

Connecting DC when no USB present

Connecting DC with USB present

ms

µs

Input Current Soft-Start Time

Thermal-Limit Temperature

Die temperature at which charging and input current limits

are reduced

+100

°C

Thermal-Limit Gain

VL Voltage

I

reduction/die temperature (above +100°C)

5

%/°C

V

SYS

= 0 to 10mA

3.0

3.3

3.6

VL

2

_______________________________________________________________________________________

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

MAX867C

ELECTRICAL CHARACTERISTICS (continued)

(V

= 5V, THM = CEN = USUS = GND, V

= 4V, V

= V

= 5V, USB, TSET, PREQ, CHG, DOK, UOK, FLT are unconnected,

DC

BAT

PEN1

PEN2

T = -40°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.) (Note 1)

A

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

USB-TO-SYS PREREGULATOR

USB Operating Range

4.1

6.6

8

V

USB Standoff Voltage

V

= V

= 0V

BAT

SYS

UOK

USB Undervoltage Threshold

USB Overvoltage Threshold

When V

goes low, V

rising, 500mV hysteresis

3.95

6.8

4.0

6.9

1

4.05

7.0

2

USB

goes high, V

rising, 100mV hysteresis

USB

I

= I

= 0mA, V

= 0V, V

= 5V, V

= 0V

USUS

SYS

BAT

CEN

PEN2

USB Supply Current

mA

0.9

190

0.2

1.5

333

0.31

PEN2

USB Shutdown Current

DC = unconnected, V

= V

= 5V

= 400mA

µA

USB

CEN

USB-to-SYS On-Resistance

= 5V, I

Ω

SYS

When SYS regulation and charging stops, V

250mV hysteresis

falling,

USB

USB-to-BAT Drop-Out Voltage

10

450

80

50

475

95

90

mV

mA

V

= 0V,

= 5V

PEN1

PEN2

500

100

4.40

USB Current Limit

(See Table 2 for Input Source

Control)

DC = unconnected,

= 5V,

V

USB

V

= 0V,

= 0V

PEN1

PEN2

T

A

= +25°C

DC = unconnected, V

= 6V;

USB

SYS Regulation Voltage

4.29

4.35

I

= 1mA to 400mA, V

= 5V

CEN

SYS

Input Limiter Soft-Start Time

Thermal-Limit Start Temperature

Thermal-Limit Gain

Input current ramp time

50

+100

5

µs

°C

I

reduction/die temperature (above +100°C)

%/°C

V

SYS

VL Voltage

DC = unconnected, V

= 5V; I = 0 to 10mA

3.0

40

3.3

3.6

USB

VL

CHARGER

BAT-to-SYS On-Resistance

V

= 0V, V

= 4.2V, I = 1A

SYS

0.04

68

0.08

90

Ω

DC

BAT

BAT-to-SYS Reverse Regulation

Voltage

= V

= 0V, I = 200mA

SYS

mV

PEN1

PEN2

T

= +25°C

4.179

4.158

-135

0.3

4.2

-95

4.221

4.242

-45

A

BAT Regulation Voltage

I

= 0mA

V

BAT

= 0°C to +85°C

A

BAT Recharge Threshold

Change in V

from DONE to fast-charge

mV

A

BAT

BAT Charge-Current Set Range

R

= 10kΩ to 2kΩ (Note 2)

1.5

ISET

R

ISET

R

ISET

R

ISET

= 2.4kΩ

= 4kΩ

1125

675

1250

750

1375

825

= 10kΩ

270

300

330

R

= 4kΩ, V

= 2.5V

BAT

ISET

50

23

75.0

48

100

73

BAT Charge-Current Accuracy,

Charger Loop in Control

V

= 5.5V,

= 0°C to +85°C

SYS

(prequal mode)

mA

T

A

R

ISET

= 6.2kΩ, V

= 2.5V

BAT

(prequal mode)

R

= 10kΩ, V

= 2.5V

BAT

ISET

30

(prequal mode)

_______________________________________________________________________________________

3

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

ELECTRICAL CHARACTERISTICS (continued)

(V

= 5V, THM = CEN = USUS = GND, V

= 4V, V

= V

= 5V, USB, TSET, PREQ, CHG, DOK, UOK, FLT are unconnected,

DC

BAT

PEN1

PEN2

T = -40°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.) (Note 1)

A

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

R

(V

= 4kΩ, I

= 500mA

ISET

BAT

ISET Voltage

0.9

1.0

1.1

V

= 1.5V at full charge current)

ISET

Charger Soft-Start Time

BAT Prequal Threshold

Charge-current ramp time

1.5

3

ms

V

rising, 180mV hysteresis

2.9

3.1

6

BAT

MAX867C

No DC or USB power connected

DC or USB connected, V = 5V

3

BAT Leakage Current

V

= 4.2V

µA

BAT

3

6

CEN

V

= 0

5

TSET

DONE Threshold as a

Percentage of Fast-Charge

I

decreasing

= open

10

15

BAT

%

= V

L

From V

falling to end of prequal charge,

CEN

Maximum Prequal Time

30

Min

V

= 2.5V, C = 0.068µF

T

BAT

Maximum Fast-Charge Time

Timer Accuracy

From V

falling to V

falling, C = 0.068µF

300

Min

%

CEN

FLT

T

C = 0.068µF

T

-20

+20

Percentage of fast-charge current below which timer

clock operates at half speed

Timer Extend Threshold

Timer Suspend Threshold

50

20

%

Percentage of fast-charge current below which timer

clock pauses

THM

THM Threshold, Cold

THM Threshold, Hot

THM Threshold, Disabled

When charging is suspended, 2% hysteresis

When THM function is disabled

72

26

74

28

76

30

% of V

L

3

THM = GND or V ; T = +25°C

-0.1

1.3

0.001

0.01

+0.2

L

A

THM Input Leakage

µA

THM = GND or V ; T = +85°C

L

A

LOGIC I/O: CHG, FLT, PREQ, DOK, UOK, PEN1, PEN2, CEN, TSET, USUS

High level

V

Logic Input Thresholds

Low level

Hysteresis

High level

Midlevel

0.4

50

mV

V - 0.3

L

TSET Input Threshold

V

1.2

V - 1.2

L

Low level

TSET = GND

0.3

-20

-6

6

TSET Input-Bias Current

µA

TSET = V

L

20

1

T

= +25°C

= +85°C

0.001

0.01

25

A

Logic Input-Leakage Current

Logic Output Voltage, Low

V

= 0 to 5.5V

µA

mV

µA

INPUT

A

Sinking 1mA

= 5.5V

100

1

T

= +25°C

= +85°C

0.001

0.01

A

Logic Output-Leakage Current,

High

V

OUT

A

Note 1: Limits are 100% production tested at T = +25°C. Limits over the operating temperature range are guaranteed by design.

A

Note 2: Guaranteed by design.

4

_______________________________________________________________________________________

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

MAX867C

Typical Operating Characteristics

(T = +25°C, unless otherwise noted.)

A

USB QUIESCENT CURRENT

vs. USB VOLTAGE (CHARGER ENABLED)

USB QUIESCENT CURRENT

vs. USB VOLTAGE (CHARGER DISABLED)

USB QUIESCENT CURRENT

vs. USB VOLTAGE (SUSPEND)

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

1.2

0.40

V

= 4.2, V

= 0V

V

= 4.2, V

= 0V

V = 4.2, USUS = 1

BAT

USUS

BAT

USUS

V

RISING

FALLING

USB

0.35

0.30

0.25

0.20

CEN = 1

= 0V

PEN1 = X, PEN2 = 1

CHARGER IN

DONE MODE

1.0

0.8

I

SYS

PEN1 = X, PEN2 = 1

I

= 0V

SYS

PEN1 = X, PEN2 = 1

V

RISING

FALLING

USB

0.6

0.4

0.2

0

0.15

0.10

ENTERING OVLO

EXITING UVLO

0.05

0

ENTERING OVLO

EXITING UVLO

0

1

2

3

4

5

6

7

8

0

1

2

3

4

5

6

7

8

85

5

0

1

2

3

4

5

6

7

8

USB VOLTAGE (V)

BATTERY LEAKAGE CURRENT

vs. BATTERY VOLTAGE (USB DISCONNECTED)

BATTERY LEAKAGE CURRENT

vs. TEMPERATURE

BATTERY LEAKAGE CURRENT

vs. BATTERY VOLTAGE (USB CONNECTED)

4.0

3.60

3.58

3.56

3.54

7

6

5

4

USB = OPEN

V

= 4V

V

= 5V

USB

USUS = 1

CEN = 1

BAT

3.5

3.0

2.5

2.0

3.52

3.50

3.48

3.46

3

2

1

0

1.5

1.0

0.5

0

1

2

3

4

5

-40

-15

10

35

60

0

1

2

3

4

5

BATTERY VOLTAGE (V)

TEMPERATURE (°C)

BATTERY VOLTAGE (V)

CHARGE CURRENT

vs. BATTERY VOLTAGE (100mA USB)

vs. BATTERY VOLTAGE (500mA USB)

vs. BATTERY VOLTAGE (1ADC)

100

90

500

450

400

1.2

1.0

0.8

0.6

0.4

0.2

V

= 5V

V

= 5V

DC

PEN1 = 1 , PEN2 = X

USB

PEN1 = X, PEN2 = 1

80

V

RISING

FALLING

V

RISING

FALLING

BAT

70

60

50

40

350

300

250

200

V

= 5V

USB

PEN1 = X , PEN2 = 1

V

RISING

FALLING

BAT

30

20

10

0

150

100

50

0

1

2

3

4

5

0

1

2

3

4

0

1

2

3

4

5

BATTERY VOLTAGE (V)

_______________________________________________________________________________________

5

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

Typical Operating Characteristics (continued)

(T = +25°C, unless otherwise noted.)

A

SYS OUTPUT VOLTAGE

vs. USB VOLTAGE

NORMALIZED CHARGE CURRENT vs. AMBIENT

TEMPERATURE (LOW IC POWER DISSIPATION)

1.0100

BATTERY REGULATION VOLTAGE

vs. TEMPERATURE

4.40

4.35

4.30

4.25

4.20

4.15

4.10

4.05

4.00

4.205

4.200

V

= 5V, V = 4V

BAT

V

= 4V

NO SYS LOAD

USB

BAT

1.0075

1.0050

1.0025

1.0000

0.9975

0.9950

0.9925

0.9900

MAX867C

4.195

4.190

4.185

4.180

40ppm/°C

0

1

2

3

4

5

6

7

8

-40

-15

10

35

60

85

-40

-15

10

35

60

85

V

(V)

AMBIENT TEMPERATURE (°C)

TEMPERATURE (°C)

USB

SYS OUTPUT VOLTAGE

vs. DC VOLTAGE

SYS OUTPUT VOLTAGE vs. SYS OUTPUT

CURRENT (USB AND DC DISCONNECTED)

SYS OUTPUT VOLTAGE

vs. SYS OUTPUT CURRENT (DC)

4.40

4.35

4.5

4.4

5.5

V

= 4V

V

= 4V

BAT

V

= 4V

BAT

NO SYS LOAD

PEN1 = 1, PEN2 = X

CEN = 1

THE SLOPE OF THIS LINE

SHOWS THAT THE BAT-TO-SYS

RESISTANCE IS 40mΩ

5.1

4.7

4.3

4.2

4.1

4.30

4.25

4.20

4.15

4.10

4.05

4.00

4.0

3.9

3.8

3.7

3.6

4.3

3.9

3.5

0

2

4

6

8

10

12

14

0

0.5

1.0

(A)

1.5

2.0

0

0.5

1.0

1.5

(A)

2.0

2.5

3.0

V

(V)

DC

I

SYS

SYS OUTPUT VOLTAGE

vs. SYS OUTPUT CURRENT

VL OUTPUT VOLTAGE

vs. DC VOLTAGE

5.1

4.9

4.7

3.5

V

= 4V

= 5V

BAT

USB

3.0

2.5

2.0

PEN1 = X

CEN = 1

I

= 10mA

VL

4.5

4.3

I

= 0mA

VL

500mA USB

1.5

1.0

4.1

3.9

3.7

0.5

0

100mA

0.5

3.5

0

1.0

1.5

(A)

2.0

2.5

3.0

0

2

4

6

8

(V)

10

12

14

I

V

SYS

DC

6

_______________________________________________________________________________________

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

MAX867C

Typical Operating Characteristics (continued)

(T = +25°C, unless otherwise noted.)

A

CHARGE PROFILE —1400mAh BATTERY

ADAPTER INPUT—1A CHARGE

USB INPUT—500mA CHARGE

MAX8677C toc18

MAX8677C toc19

6.0

5.5

1.2

5.0

4.5

4.0

0.50

0.45

0.40

0.35

V

BAT

V

BAT

5.0

4.5

4.0

3.5

1.0

0.8

I

BAT

3.5

0.30

0.25

0.20

I

BAT

3.0

2.5

2.0

1.5

1.0

0.5

0.6

0.4

0.2

0

2.5

2.0

1.5

1.0

0.5

0.15

0.10

0.05

0

50

100

150

0

20 40 60

80 100 120 140 160 180

TIME (min)

DC CONNECT WITH USB CONNECTED

(R = 25Ω)

DC CONNECT WITH NO USB

(R

= 25Ω)

SYS

4.35V

SYS

MAX8677C toc20

MAX8677C toc21

V

BAT

3.68V

3.6V

4.35V

C CHARGING

SYS

3.6V

V

SYS

3.6V

CHARGING

SYS

2V/div

C

DC

CHARGING

C

DC

C

CHARGING

500mA

SYS

1.2A

I

0A

DC

500mA/div

I

DC

0A

500mA/div

I

500mA

0A

USB

NEGATIVE BATTERY

CURRENT FLOWS INTO

THE BATTERY (CHARGING)

120mA

NEGATIVE BATTERY CURRENT

FLOWS INTO THE BATTERY

(CHARGING)

0A

I

BAT

I

BAT

BATTERY

500mA/div

-1A

BATTERY

CHARGER

SOFT-START

CHARGER

SOFT-START

-335mA

-330mA

200μs/div

400μs/div

DC DISCONNECT WITH NO USB

(R = 25Ω)

USB CONNECT WITH NO DC

(R

= 20Ω)

SYS

5V

CHARGING

MAX8677C toc22

MAX8677C toc23

V

I

10V/div

USB

0V

3.6V

4.35V

1.2A

V

C

SYS

USB

C

CHARGING

SYS

500mA/div

USB

500mA

4.3V

0A

500mA/div

4.35V

I

DC

0A

3.6V

V

SYS

V

5V/div

UOK

0V

3V

0.2A

V

CHG

I

BAT

NEGATIVE BATTERY

CURRENT FLOWS INTO

THE BATTERY (CHARGING)

I

BAT

-1A

155mA

-300mA

500mA/div

BATTERY

CHARGER SOFT-START

20μs/div

200μs/div

_______________________________________________________________________________________

7

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

Typical Operating Characteristics (continued)

(T = +25°C, unless otherwise noted.)

A

USB DISCONNECT WITH NO DC

(R

SYS

= 20Ω)

USB SUSPEND

MAX8677C toc24

MAX8677C toc25

5V

0V

V

I

V

USUS

USB

10V/div

3V

0A

5V/div

475mA

500mA/div

500mA

3.7V

I

USB

500mA/div

0A

V

SYS

3.7V

V

3.6V

3V

MAX867C

3.6V

SYS

5V/div

0V

V

CHG

UOK

CHG

3V

0V

5V/div

0V

-300mA

V

120mA

1A/div

0A

500mA/div

-500mA

200μs/div

USB RESUME

MAX8677C toc26

V

USUS

0V

CHARGING

5V/div

3V

USB

C

I

500mA/div

500mA

3.7V

USB

0A

3.6V

3V

4.35V

0V

V

SYS

V

CHG

5V/div

500mA/div

0A

BATTERY

CHARGER SOFT-START

-500mA

200μs/div

Pin Description

NAME

FUNCTION

Charge Prequal Output. Active-low, open-drain output pulls low when the charger enters the prequal state.

See Figure 5.

1

PREQ

DC Power Input. DC is capable of delivering up to 2A to SYS. DC supports both AC adapter and USB inputs. The

2, 3

DC

DC current limit is set with PEN1, PEN2, USUS, and R . See Table 2. Both DC pins must be connected

PSET

together externally.

Charger Enable Input. Connect CEN to GND to enable battery charging when a valid source is connected at DC

or USB. Connect to VL or drive high with a logic signal to disable battery charging.

4

5

CEN

DC Input Limit Control. If PEN1 is high, the DC input current limit is 3000/R

by PEN2 and USUS. See Table 2.

. If PEN1 is low, the DC limit is set

PSET

PEN1

8

_______________________________________________________________________________________

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

MAX867C

Pin Description (continued)

6

NAME

PEN2

PSET

VL

FUNCTION

USB High/Low Control. PEN2 sets the DC or USB current limit to 100mA (PEN2 low) or 500mA (PEN2 high).

PEN2 controls both DC and USB current limits when PEN1 is low. See Table 2.

7

DC Input Current-Limit Set. Connect a resistor to ground to program the DC current limit to 3000/R

.

PSET

Logic LDO Output. VL is the output of an LDO that powers the MAX8667A internal circuitry. VL also provides

3.3V at up to 10mA to power external circuitry. Connect a 0.1µF capacitor from VL to GND.

8

9

GND

CT

Ground

Charge Timer Program Pin. A capacitor from CT to GND sets the fast-charge (t

fault timers. Connect to GND to disable the timer.

) and prequal (t

)

PREQUAL

FSTCHG

10

Charge Current Set Input. A resistor (R

The prequal charge current is 10% of the set maximum charge current.

) from ISET to GND programs the maximum charge current up to 1.5A.

ISET

11

12

ISET

THM

Thermistor Input. Connect a negative temperature coefficient (NTC) thermistor that has good thermal contact

with the battery from THM to GND. Connect a resistor equal to the thermistor +25°C resistance from THM to VL.

Charging is suspended when the thermistor is outside the hot and cold limits. Connect THM to GND to disable

the thermistor temperature sensor.

USB Suspend Input. With PEN1 low, driving USUS high turns off both the USB and DC inputs. With PEN1 high,

driving USUS high turns off only the USB input. See Table 2.

13

14

USUS

TSET

USB

Termination Current Set Pin. Connect to GND, leave open, or connect to VL for a 5%, 10%, or 15% (of I

)

CHGMAX

termination current (I

) threshold.

TERM

USB Power Input. USB is capable of delivering up to 0.5A to SYS. The USB current limit is set with PEN2 and

USUS. See Table 2. Both USB pins must be connected together externally.

15, 16

Battery Connection. Connect to a single-cell Li+ battery. The battery charges from SYS when a valid source is

present at DC or USB. BAT powers SYS when neither DC nor USB power is present, or when the SYS load

exceeds the input current limit. Both BAT pins must be connected together externally.

17, 18

19

BAT

Charger Status Output. Active-low, open-drain output pulls low when the battery is in fast-charge or prequal.

Otherwise, CHG is high impedance.

CHG

System Supply Output. SYS is connected to BAT through an internal 40mΩ system load switch when DC or USB

is invalid, or when the SYS load is greater than the input current limit.

When a valid voltage is present at DC or USB, SYS is limited to 4.35V. When the system load (I

DC or USB current limit, SYS is regulated to 68mV below BAT, and both the USB input and the battery service SYS.

) exceeds the

SYS

20, 21

SYS

Bypass SYS to GND with a 10µF X5R or X7R ceramic capacitor. Both SYS pins must be connected together

externally.

22

23

DOK

UOK

DC Power-OK Output. Active-low, open-drain output pulls low when a valid input is detected at DC.

USB Power-OK Output. Active-low, open-drain output pulls low when a valid input is detected at USB.

Fault Output. Active-low, open-drain output pulls low when the battery timer expires before prequal or

fast-charge complete.

24

—

FLT

Exposed Paddle. Connect the exposed paddle to GND. Connecting the exposed paddle does not remove the

requirement for proper ground connections to the appropriate pins.

EP

_______________________________________________________________________________________

9

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

DC POWER

MANAGEMENT

MAX8677C

TO

SYSTEM

LOAD

DC

SYS

ISET

AC

ADAPTER

PWR

OK

MAX867C

CURRENT-

LIMITED

VOLTAGE

Li+ BATTERY CHARGER

AND SYS LOAD SWITCH

DOK

REGULATOR

CHARGER

CURRENT-

VOLTAGE

CONTROL

SET

INPUT

LIMIT

BAT

THM

VL

BAT+

BAT-

NTC

T

USB POWER

MANAGEMENT

THERMISTOR

MONITOR

(SEE FIGURE 7)

USB

UOK

USB

PWR

OK

IC

CURRENT-

LIMITED

VOLTAGE

CHG

CHARGE

TERMINATION

AND MONITOR

THERMAL

REGULATION

PREQ

REGULATOR

VL = 15%

N.C. = 10%

5%

TSET

SET

INPUT

LIMIT

FLT

CT

CHARGE

TIMER

PEN1

PEN2

USUS

PSET

DC MODE

CEN

GND

500mA

USB

LIMIT

INPUT AND

CHARGER

CURRENT LIMIT

SET LOGIC

100mA

USB

SUSPEND

EP

DC

LIMIT

Figure 1. Block Diagram

charger has two power inputs, DC and USB. These can

be separately connected to an AC adapter output and

a USB port, or the DC input can be a single power

input that connects to either an adapter or USB. Logic

inputs, PEN1 and PEN2, select the correct current limits

Circuit Description

The MAX8677C contains an Li+ battery charger, as

well as power MOSFETs and control circuitry to man-

age power flow in portable devices. See Figure 1. The

10 ______________________________________________________________________________________

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

MAX867C

R

PU

3X 560kΩ

TO VL

R

PU

560kΩ

1

2

24

23

22

21

20

19

18

17

16

15

14

13

FAULT

OUTPUT

PREQUAL

ADAPTER

PREQ

DC

FLT

MAX8677C

USB PWR

OK

UOK

C

DC

4.7μF

3

DC

DC PWR

OK

DOK

SYS

OFF

CHARGE ON

4

TO SYSTEM

LOAD

CEN

PEN1

PEN2

PSET

VL

C

10μF

SYS

5

560kΩ

TO VL

500mA

6

CHARGE

INDICATOR

CHG

BAT

100mA

7

1-CELL

Li+

C

BAT

R

PSET

4.7μF

BAT

USB

8

C

L

USB

0.1μF

9

VBUS

GND

CT

C

T

C

USB

4.7μF

0.068μF

10

11

12

ISET

THM

TSET

R

ISET

TO VL: I

= 15%

TERM

OPEN: I

GND: I

= 10%

TERM

USUS

10kΩ

= 5%

TERM

NTC

10kΩ

+25°C

USB SUSPEND

Figure 2. Typical Application Circuit Using Separate DC and USB Connectors

for two-input or single-input operation. Figure 2 is the

typical application circuit using separate DC and USB

connectors. Figure 3 is the typical application circuit

using a Mini 5-style connector or other DC/USB com-

mon connector.

The charging current is also provided from SYS so that

the set input current limit controls the total SYS current,

which is the sum of the system load current and the

battery-charging current. SYS is powered from either

the DC input pin or the USB input pin. If both the DC

and USB are connected, DC takes precedence.

In addition to charging the battery, the MAX8677C also

supplies power to the system through the SYS output.

______________________________________________________________________________________ 11

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

3X 560kΩ

TO VL

560kΩ

1

2

24

23

22

21

20

19

18

17

16

15

14

13

MINI 5-STYLE

CONNECTOR

FAULT

OUTPUT

PREQUAL

PREQ

DC

FLT

MAX8677C

1

2

3

4

5

USB PWR

OK

MAX867C

VBUS

D-

UOK

C

DC

4.7μF

3

DC

DC PWR

OK

D+

DOK

SYS

ID

OFF

4

TO SYSTEM

LOAD

GND

CHARGE

CEN

PEN1

PEN2

PSET

VL

ON

C

10μF

SYS

HI = DC

SYS

5

DC-USB ID

560kΩ

LO = USB

TO VL

500mA

6

CHARGE

INDICATOR

CHG

BAT

100mA

7

1-CELL

Li+

C

BAT

R

PSET

4.7μF

BAT

USB

8

C

L

0.1μF

9

GND

CT

C

T

0.068μF

10

11

12

ISET

THM

TSET

R

ISET

TO VL: I

= 15%

TERM

OPEN: I

GND: I

= 10%

TERM

USUS

10kΩ

= 5%

TERM

NTC

10kΩ

+25°C

USB SUSPEND

Figure 3. Typical Application Circuit Using Mini 5-Style Connector or Other DC/USB Common Connector

In some instances, there may not be enough adapter

current or USB current to supply peak system loads.

The MAX8677C Smart Power Selector circuitry offers

flexible power distribution from an AC adapter or USB

source to the battery and system load. The battery is

charged with any available power not used by the sys-

tem load. If a system load peak exceeds the input

current limit, supplemental current is taken from the bat-

tery. Thermal limiting prevents overheating by reducing

power drawn from the input source. In the past, it might

have been necessary to reduce system functionality to

limit current drain when a USB source is connected.

However, in the MAX8677C, this is no longer the case.

When the DC or USB source hits its limit, the battery

supplies supplemental current to maintain the load.

12 ______________________________________________________________________________________

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

MAX867C

Table 1. External Components List for Figures 2 and 3

COMPONENT

(FIGURES 2, 3)

FUNCTION

PART

C

Input filter capacitor

4.7µF ceramic capacitor

0.1µF ceramic capacitor

10µF ceramic capacitor

4.7µF ceramic capacitor

IN

CL

VL filter capacitor

C

SYS output bypass capacitors

Battery bypass capacitor

SYS

BAT

C

CT

(x 4)

Charger timing capacitor

0.068µF low TC ceramic capacitor

R

Logic output pullup resistors

Negative TC thermistor

560kΩ

PU

THM

RT

Phillips NTC thermistor, P/N 2322-640-63103, 10kΩ 5% at +25°C

THM pullup resistor

10kΩ 1%

R

Input current-limit programming resistor

Fast-charge current programming resistor

1.5kΩ 1% for 2A limit

3kΩ 1% for 1A charging

PSET

R

ISET

The MAX8677C features OVP. Part of this protection is

a 4.35V voltage limiter at SYS. If the DC or USB input

exceeds 4.35V, SYS still limits at 4.35V.

System Load Switch

An internal 40mΩ MOSFET connects SYS to BAT (Q3,

Figure 4) when no voltage source is available at DC or

USB. When an external source is detected at DC or

USB, this switch is opened and SYS is powered from

the valid input source through the input limiter.

The MAX8677C has numerous other charging and

power-management features, which are detailed in the

following sections.

The SYS-BAT switch also holds up SYS when the sys-

tem load exceeds the input current limit. If that should

happen, the SYS-BAT switch turns on so that the bat-

tery supplies additional SYS load current. If the system

load continuously exceeds the input current limit, the

battery does not charge, even though external power is

connected. This is not expected to occur in most

cases, since high loads usually occur only in short

peaks. During these peaks, battery energy is used, but

at all other times the battery charges.

Smart Power Selector

The MAX8677C Smart Power Selector seamlessly dis-

tributes power between the external inputs, the battery,

and the system load (Figure 4). The basic functions

performed are:

•

With both an external power supply (USB or

adapter) and battery connected:

When the system load requirements are less

than the input current limit, the battery is

charged with residual power from the input.

AC

When the system load requirements exceed the

input current limit, the battery supplies supple-

mental current to the load.

ADAPTER

SYS

LOAD

DC

Q1

CHARGE

CURRENT

SYSTEM

LOAD

•

When the battery is connected and there is no

external power input, the system is powered from

the battery.

USB

Q2

Q3

When an external power input is connected and

there is no battery, the system is powered from the

external power input.

BAT

BATTERY

CHARGE AND

SYS LOAD

SWITCH

A thermal-limiting circuit reduces the battery charge

rate and external power-source current to prevent the

MAX8677C from overheating.

GND

MAX8677C

Figure 4. Smart Power Selector Block Diagram

______________________________________________________________________________________ 13

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

•

Thermal Limiting. The MAX8677C reduces input lim-

iter current by 5%/°C when its die temperature

exceeds +100°C. The system load (SYS) has priority

over the charger current, so input current is first

reduced by lowering charge current. If the junction

temperature still reaches +120°C in spite of charge-

current reduction, no input (DC or USB) current is

drawn, the battery supplies the entire system load, and

SYS is regulated at 68mV below BAT. Note that this

on-chip thermal-limiting circuitry is not related to and

operates independently from the thermistor input.

Input Limiter

The input voltage limiter is essentially an LDO regulator.

While in dropout, the regulator dissipates a small I²R loss

through the 0.2Ω MOSFET (Q1, Figure 4) between DC

and SYS. With an AC adapter or USB source connect-

ed, the input limiter distributes power from the external

power source to the system load and battery charger.

In addition to the input limiter’s primary function of

passing power to the system and charger loads at SYS,

it performs several additional functions to optimize use

of available power:

MAX867C

•

Adaptive Battery Charging. While the system is

powered from DC, the charger draws power from

SYS to charge the battery. If the charger load plus

system load exceeds the input current limit, an

adaptive charger control loop reduces charge cur-

rent to prevent the SYS voltage from collapsing.

Maintaining a higher SYS voltage improves efficien-

cy and reduces power dissipation in the input limiter.

•

Input Voltage Limiting. If an input voltage is above

the overvoltage threshold (6.9V typ), the MAX8677C

enters overvoltage lockout (OVLO). OVLO protects

the MAX8677C and downstream circuitry from high-

voltage stress up to 14V at DC and 8V at USB. In

OVLO, VL remains on, the input switch that sees

overvoltage (Q1, Q3, Figure 4) opens, and the

appropriate power-monitor output (DOK, UOK) is

high impedance, and CHG is high impedance.

The total current through the switch (Q1 or Q2 in

Figure 4) is the sum of the load current at SYS and

the battery charging current. The limiter clamps at

4.35V, so input voltages greater than 4.35V can

increase power dissipation in the limiter. The limiter

If both DC and USB see overvoltage, both input

switches (Q1 and Q2, Figure 4) open and the

charger turns off. The BAT-SYS switch (Q3, Figure

4) closes, allowing the battery to power SYS.

power loss is (V

- 4.35) x I, but not less than I²x

DC

An input is also invalid if it is less than BAT, or less

than the DC undervoltage threshold of 3.5V (falling).

With an invalid input voltage, SYS connects to BAT

through a 40mΩ switch (Q3, Figure 4).

0.2Ω. Also note that the MAX8677C turns off any

input that exceeds 6.9V (nominal).

DC and USB Connections and

Current-Limit Options

•

Input Overcurrent Protection. The current at DC

and USB is limited to prevent input overload. This cur-

rent limit can be selected to match the capabilities of

the source, whether it is a 100mA or 500mA USB

source, or an AC adapter. When the load exceeds

the input current limit, SYS drops to 68mV below BAT

and the battery supplies supplemental load current.

Input Current Limit

The input and charger current limits are set as shown in

Table 2. It is often preferable to change the input cur-

rent limit as the input power source is changed. The

MAX8677C facilitates this by allowing different input

current limits for DC and USB as shown in Table 2.

Table 2. Input Limiter Control Logic

DC INPUT

CURRENT

LIMIT

USB INPUT

CURRENT

LIMIT

MAXIMUM

CHARGE

CURRENT*

POWER SOURCE

DOK

UOK

PEN1

PEN2

USUS

AC adapter at DC input

L

X

L

H

L

X

L

X

L

3000/R

ISET

PSET

USB input off;

DC input has

priority

100mA

USB power at DC input

L

H

X

L

500mA

0

L

H

L

USB suspend

H

100mA

500mA

3000/R

ISET

USB power at USB input;

DC unconnected

H

X

L

No DC input

H

X

USB suspend

No USB input

0

DC and USB unconnected

*Charge current cannot exceed the input current limit. Charge may be less than the maximum charge current if the total SYS load

exceeds the input current limit.

14 ______________________________________________________________________________________

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

MAX867C

When the input current limit is reached, the first action

Soft-Start

To prevent input transients that can cause instability in

the USB or AC adapter power source, the rate of change

of input current and charge current is limited. When a

valid DC or USB input is connected, the input current limit

is ramped from zero to the set current-limit value (as

shown in Table 2). If DC is connected with no USB power

present, input current ramps in 1.5ms. If DC is connected

with USB already present, input current ramps in 50µs.

When USB is connected with no DC present, input cur-

rent also ramps in 50µs. If USB is connected with DC

already present, the USB input is ignored.

taken by the MAX8677C is to reduce the battery charge

current. This allows the regulator to stay in dropout, or

at 4.35V, during heavy loads, thus reducing power dis-

sipation. If, after the charge current is reduced to 0mA,

the load at SYS still exceeds the input current limit, SYS

begins to fall. When the SYS voltage drops to BAT, the

SYS-BAT switch turns on, using battery power to sup-

port the system load during the load peak.

The MAX8677C features flexible input connections (at

the DC and USB input pins) and current-limit settings

(set by PEN1, PEN2, PSET, and ISET) to accommodate

nearly any input power configuration. However, it is

expected that most systems use one of two external

power schemes: separate connections for USB and an

AC adapter, or a single connector that accepts either

USB or AC adapter output. Input and charger current

If an adapter is plugged into DC while USB is already

powered, the input current limit reramps from zero back

up to the DC current limit so that the AC adapter does

not see a load step. During this transition, if the input

current limit is below the SYS load current, the battery

supplies the additional current needed to support the

load. Additionally, capacitance can be added to SYS to

support the load during input power transitions.

limit are controlled by PEN1, PEN2, R

as shown in Table 2.

, and R

,

PSET

ISET

Separate Adapter and USB Connectors

When the AC adapter and USB have separate connec-

tors, the adapter output connects to DC and the USB

source connects to USB. PEN1 is permanently tied high

When the charger is turned on, charge current ramps

from zero to the ISET current value in typically 1.5ms.

Charge current also ramps when transitioning to fast-

charge from prequal and when changing the USB

charge current from 100mA to 500mA with PEN2. There

is no dI/dt limiting, however, if ISET is changed suddenly

(to DC or VL). The DC current limit is set by R

,

PSET

while the USB current limit is set by PEN2 and USUS.

using a switch at R

.

Single Common Connector for USB or Adapter

When a single connector is used for both AC adapter

and USB sources, the DC input is used for both input

sources. When an AC adapter is connected at DC,

PEN1 should be pulled high to select the current limit

ISET

Battery Charger

The battery charger state diagram is illustrated in

Figure 5. With a valid DC or USB input, the battery

charger initiates a charge cycle when the charger is

enabled. It first detects the battery voltage. If the bat-

tery voltage is less than the BAT prequal threshold

(3.0V), the charger enters prequal mode in which the

battery charges at 10% of the maximum fast-charge

current. This reduced charge rate ensures that the bat-

tery is not damaged by the fast-charge current while

deeply discharged. Once the battery voltage rises to

3.0V, the charger transitions to fast-charge mode and

applies the maximum charge current. As charging con-

tinues, the battery voltage rises until it approaches the

battery regulation voltage (4.2V) where charge current

starts tapering down. When charge current decreases

to 5%, 10%, or 15% (as set by TSET) of the fast-charge

current, the charger enters a brief 15s top-off, and then

charging stops. If the battery voltage subsequently

drops below the 4.1V recharge threshold, charging

restarts and the timers reset.

set by R

. When a USB source is connected, PEN1

PSET

should be low to select 500mA, 100mA, or USB sus-

pend (further selected by PEN2 and USUS). PEN1 can

be pulled up by the AC adapter power to implement

hardware adapter/USB selection.

USB Suspend

Driving USUS high when PEN1 is low turns off charging,

as well as the SYS output and reduces input current to

190µA to accommodate USB suspend mode.

Power Monitor Outputs (UOK, DOK)

DOK is an open-drain output that pulls low when the

DC input has valid power. UOK is an open-drain output

that pulls low when the USB input sees valid power. A

valid input for DC or USB is between 4.1V and 6.6V. If a

single power-OK output is preferred, DOK and UOK

can be wire-ORed together. The combined output then

pulls low if either USB or DC sees a valid input.

______________________________________________________________________________________ 15

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

CEN = HI

OR

NOT READY

REMOVE AND RECONNECT

THE INPUT SOURCE(S).

UOK AND DOK = HIGH IMPEDANCE

ANY STATE

CHG = HIGH IMPEDANCE

FLT = HIGH IMPEDANCE

PREQ = HIGH IMPEDANCE

I

= 0mA

CHG

TOGGLE CEN

OR

UOK OR DOK = LOW

MAX867C

REMOVE AND RECONNECT

THE INPUT SOURCE(S).

CEN = 0

RESET TIMER

PREQUAL

TIMER > t

PREQUAL

UOK OR DOK = LOW

CHG = LOW

FLT = HIGH IMPEDANCE

PREQ = LOW

0V ≤ V

≤ 3V

/10

BATT

FAULT

UOK OR DOK = LOW

CHG = HIGH IMPEDANCE

FLT = LOW

I

= I

CHG CHGMAX

V

< 2.82V,

RESET TIMER

V

BATT

> 3V,

BATT

RESET TIMER

PREQ = PREVIOUS STATE

FAST CHARGE

I

= 0mA

CHG

UOK OR DOK = LOW

CHG = LOW

FLT = HIGH IMPEDANCE

PREQ = HIGH IMPEDANCE

V

< 2.8V

BATT

TIMER > t

FSTCHG

RESET TIMER

3V < V

< 4.2V

BATT

(TIMER SLOWED BY 2X IF

< I /2, AND

I

≤ I

CHG CHGMAX

I

CHG CHGMAX

PAUSED IF I

< I

/5

CHG CHGMAX

I

< I

BAT

CHG TERM

WHILE BAT < 4.2V)

AND V = 4.2V

I

> I

AND THERMAL

OR INPUT LIMIT

NOT EXCEEDED.

RESET TIMER.

CHG TERM

RESET TIMER

ANY CHARGING

STATE

TOP-OFF

UOK OR DOK = LOW

CHG = HIGH IMPEDANCE

FLT = HIGH IMPEDANCE

PREQ = HIGH IMPEDANCE

BATT = 4.2V

THM OK

TIMER RESUME

THM NOT OK

TIMER SUSPEND

V

< 4.1V

BAT

RESET TIMER

TEMPERATURE

SUSPEND

I

< I

CHG TERM

I

= 0mA

CHG

TIMER > 15s

DONE

UOK OR DOK = PREVIOUS STATE

CHG = HIGH IMPEDANCE

FLT = HIGH IMPEDANCE

PREQ = PREVIOUS STATE

UOK OR DOK = 0V

CHG = HIGH IMPEDANCE

FLT = HIGH IMPEDANCE

PREQ = HIGH IMPEDANCE

4.1 < V

< 4.2V

BATT

I

= 0mA

CHG

Figure 5. MAX8677C Charger State Flowchart

16 ______________________________________________________________________________________

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

MAX867C

Charge Enable (CEN)

When CEN is low, the charger is on. When CEN is high,

MONITORING THE BATTERY

CHARGE CURRENT WITH V

ISET

the charger turns off. CEN does not affect the SYS out-

put. In many systems, there is no need for the system

controller (typically a microprocessor) to disable the

charger, because the MAX8677C Smart Power Selector

circuitry independently manages charging and

adapter/battery power hand-off. In these situations,

CEN can be connected to ground.

R

ISET

V

ISET

=

x I

CHG

2000

1.5

Setting the Charge Current

ISET adjusts charge current to match the capacity of

the battery. A resistor from ISET to ground sets the

maximum fast-charge current:

I

= 2000 x 1.5V/R = 3000/R

ISET ISET

CHGMAX

Determine the I

value by considering the char-

CHGMAX

0

acteristics of the battery. It is not necessary to limit the

charge current based on the capabilities of the expected

AC adapter/USB charging input, the system load, or

thermal limitations of the PCB. The MAX8677C automat-

ically adjusts the charging algorithm to accommodate

these factors.

DISCHARGING

0

2000 (1.5V / R

BATTERY CHARGING CURRENT (A)

)

ISET

Monitoring the Charge Current

In addition to setting the charge current, ISET can also

be used to monitor the actual current charging the bat-

tery. The ISET output voltage is:

Figure 6. Monitoring the Charge Current with the ISET Voltage

Leave TSET open for I

= I

x 10%

TERM

CHGMAX

Connect TSET to VL for I

= I

x 15%

TERM

CHGMAX

V

ISET

= I

x 1.5V/I

= I

x R

/2000

ISET

CHG

CHGMAX

CHG

Note that if charge current falls to I

as a result of the

TERM

where I

is the set fast-charge current and I

CHG

input or thermal limiter, the charger does not enter

DONE. For the charger to enter DONE, the charge cur-

CHGMAX

is the actual battery charge current. A 1.5V output indi-

cates the battery is being charged at the maximum set

fast-charge current; 0V indicates no charging. This volt-

age is also used by the charger control circuitry to set

and monitor the battery current. Avoid adding more

than 10pF capacitance directly to the ISET pin. If filter-

ing of the charge-current monitor is necessary, add a

resistor of 100kΩ or more between ISET and the filter

capacitor to preserve charger stability. See Figure 6.

rent must be less than I

, the charger must be in

TERM

voltage mode, and the input or thermal limiter must not

be reducing the charge current. The charger exits the

DONE state, and fast charge resumes if the battery volt-

age subsequently drops 100mV or if CEN is cycled.

Charge Status Outputs

Charge Output (CHG)

CHG is an open-drain, active-low output that is low dur-

ing charging. CHG is low when the battery charger is in

its prequalification and fast-charge states. When charge

current falls to the charge termination threshold and the

charger is in voltage mode, CHG goes high impedance.

CHG goes high impedance if the thermistor causes the

charger to enter temperature suspend mode.

Note that the actual charge current can be less than

the set fast-charge current when the charger enters

voltage mode or when charge current is reduced by

the input current limiter or thermal limiter. This prevents

the charger from overloading the input source or over-

heating the system.

Charge Termination

When the charge current falls to the termination thresh-

old AND the charger is in voltage mode, charging is

complete. Charging continues for a brief 15s top-off

period and then enters the DONE state in which charg-

When the MAX8677C is used with a microprocessor (µP),

connect a pullup resistor between CHG and the logic I/O

voltage to indicate charge status to the µP. Alternatively,

CHG can sink up to 20mA for an LED indicator.

ing stops. The termination current threshold (I

) is

TERM

Prequal Output PREQ

PREQ is an open-drain, active-low output that goes low

when the charger is in prequal state.

set by TSET to a percentage of the fast-charge current:

Connect TSET to GND for I = I x 5%

TERM

CHGMAX

______________________________________________________________________________________ 17

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

When the MAX8677C is used in conjunction with a µP,

connect a pullup resistor between PREQ and the logic I/O

voltage to indicate charge status to the µP. Alternatively,

PREQ can sink up to 20mA for an LED indicator.

To exit a fault state, toggle CEN or remove and recon-

nect the input source(s). Note also that thermistor out-

of-range or on-chip thermal-limit conditions are not

considered faults.

When the MAX8677C is used in conjunction with a µP,

connect a pullup resistor between FLT and the logic I/O

voltage to indicate fault status to the µP. Alternatively,

FLT can sink up to 20mA for an LED indicator.

Fault Output (FLT) and Charge Timer

FLT is an open-drain, active-low output that goes low

during a battery fault. The fault state occurs when either

the prequal or fast-charge timer expires. The prequal

and fast-charge fault timers are set by C

:

CT

Thermistor Input (THM)

The THM input connects to an external negative tem-

perature coefficient (NTC) thermistor to monitor battery

or system temperature. Charging is suspended when

the thermistor temperature is out of range. The charge

timers are suspended and hold their state but no fault

is indicated. When the thermistor comes back into

range, charging resumes and the charge timer contin-

ues from where it left off. Connecting THM to GND dis-

ables the thermistor monitoring function. Table 3 lists

fault temperatures for different thermistors.

MAX867C

C

CT

t

= 30min ×

PREQUAL

0.068μF

C

CT

t

= 300min ×

FSTCHG

0.068μF

While in fast-charge mode, a large system load or

device self-heating can cause the MAX8677C to

reduce charge current. Under these circumstances, the

fast-charge timer adjusts to ensure that adequate

charge time is still allowed. Consequently, the fast-

charge timer is slowed by 2x if charge current is

reduced below 50% of the programmed fast-charge

level. If charge current is reduced to below 20% of the

programmed level, the fast-charge timer is paused. The

fast-charge timer is not adjusted if the charger is in volt-

age mode where charge current reduces due to cur-

rent tapering under normal charging.

Since the thermistor monitoring circuit employs an exter-

nal bias resistor from THM to VL (R , Figure 7), the

TB

thermistor is not limited only to 10kΩ (at +25°C).

Any resistance thermistor can be used as long as the

value of R

is equivalent to the thermistor’s +25°C

TB

resistance. For example, with a 10kΩ at +25°C thermis-

tor, use 10kΩ at R , and with a 100kΩ at +25°C ther-

mistor, use 100kΩ.

TB

CEN

VL

MAX8677C

THERMISTOR CIRCUITRY

VL

R

TB

ALTERNATE

THERMISTOR

CONNECTION

0.74 VL

COLD

THM

R

TS

THM OK

HOT

0.28 VL

0.03 VL

R

TP

R

T

DISABLE

BYPASS THM

CHARGER

R

T

ALL COMPARATORS 60mV HYSTERESIS

GND

Figure 7. Thermistor Monitor Circuitry

18 ______________________________________________________________________________________

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

MAX867C

For a typical 10kΩ (at +25°C) thermistor and a 10kΩ

resistor, the charger enters a temperature suspend

Power Dissipation

It is important to ensure that the heat generated by the

MAX8677C is dissipated into the PCB. The package’s

exposed paddle must be soldered to the PCB with mul-

tiple vias tightly packed under the exposed paddle to

ensure optimum thermal contact to the ground plane.

This minimizes heat rise in the IC and ensures that

maximum charging current is maintained over the

widest range of external conditions. Table 4 shows the

thermal characteristics of the MAX8677C package.

R

TB

state when the thermistor resistance falls below 3.97kΩ

(too hot) or rises above 28.7kΩ (too cold). This corre-

sponds to a 0°C to +50°C range when using a 10kΩ

NTC thermistor with a beta of 3500. The general rela-

tion of thermistor resistance to temperature is defined

by the following equation:

⎧

⎨

⎩

⎫

⎬

⎭

1

298

⎛

⎞

β

−

⎜

⎝

⎟

⎠

R =R × e

T

25

T+273

Table 4. Package Thermal Characteristics

where:

SINGLE-LAYER

PCB

MULTILAYER

PCB

R = The resistance in Ω of the thermistor at tempe-

T

rature T in Celsius

Continuous

Power

Dissipation

1666.7mW

Derate 20.8mW/°C

above +70°C

2222.2mW

Derate 27.8mW/°C

above +70°C

R

= The resistance in Ω of the thermistor at +25°C

25

β = The material constant of the thermistor, which

typically ranges from 3000K to 5000K

θ

JA

θ

JC

48°C/W

2.7°C/W

36°C/W

2.7°C/W

T = The temperature of the thermistor in °C

Table 3 shows the MAX8677C THM temperature limits

for different thermistor material constants.

PCB Layout and Routing

Some designs might prefer other thermistor tempera-

ture limits. Threshold adjustment can be accommodat-

ed by changing R , connecting a resistor in series

TB

Good design minimizes ground bounce and voltage

gradients in the ground plane, which can result in insta-

bility or regulation errors. GND should connect to the

power-ground plane at only one point to minimize the

effects of power-ground currents. Battery ground should

connect directly to the power-ground plane. Connect

GND to the exposed paddle directly under the IC. Use

multiple tightly spaced vias to the ground plane under

the exposed paddle to help cool the IC. Position input

capacitors from DC, SYS, BAT, and USB to the power-

ground plane as close as possible to the IC. Keep high-

current traces, such as those to DC, SYS, and BAT, as

short and wide as possible. Refer to the MAX8677C

evaluation kit for a suitable PCB layout example.

and/or in parallel with the thermistor, or using a thermis-

tor with different β. For example, a +45°C hot threshold

and 0°C cold threshold can be realized by using a ther-

mistor with a β of 4250 and connecting 120kΩ in paral-

lel. Since the thermistor resistance near 0°C is much

higher than it is near +50°C, a large parallel resistance

lowers the cold threshold, while only slightly lowering

the hot threshold. Conversely, a small series resistance

raises the cold threshold, while only slightly raising the

hot threshold. Raising R lowers both the hot and cold

thresholds, while lowering R raises both thresholds.

TB

Table 3. Fault Temperatures for Different Thermistors

Thermistor β (K)

(kΩ) (Figure 7)

3000

3250

3500

10

3750

10

4250

10

R

10

TB

Resistance at +25°C (kΩ)

10

Resistance at +50°C (kΩ)

4.59

25.14

55

4.30

27.15

53

4.03

29.32

51

3.78

31.66

49

3.32

36.91

46

Resistance at 0°C (kΩ)

Nominal Hot-Trip Temperature (°C)

Nominal Cold-Trip Temperature (°C)

-3

-1

0

2

4.5

Chip Information

PROCESS: BiCMOS

______________________________________________________________________________________ 19

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information

go to www.maxim-ic.com/packages.)

MAX867C

PACKAGE OUTLINE,

12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm

1

E

21-0139

2

20 ______________________________________________________________________________________

1.5A Dual-Input USB/AC Adapter Charger

and Smart Power Selector

MAX867C

Package Information (continued)

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information

go to www.maxim-ic.com/packages.)

PACKAGE OUTLINE,

12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm

2

E

21-0139

2

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 ____________________ 21

is a registered trademark of Maxim Integrated Products, Inc.

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