AD7416/AD7417/AD7418
Figure 5 shows the method the AD7416/AD7417/AD7418 uses
to measure the device temperature. To measure
V
BE
, the sen-
sor (substrate transistor) is switched between operating currents
of I and N
×
I. The resulting waveform is passed through a
chopper-stabilized amplifier that performs the functions of
amplification and rectification of the waveform to produce a dc
voltage proportional to
V
BE
.
This voltage is measured by the ADC to give a temperature
output in 10-bit twos complement form.
The temperature resolution of the ADC is 0.25°C, which corre-
sponds to 1 LSB of the ADC. The ADC can theoretically measure
a temperature span of 255°C; the guaranteed temperature range
is –40°C to +125°C. The result of the conversion is stored in
the Temperature Value Register (00h) as a 16-bit word. The
10 MSBs of this word store the temperature measurement (see
Table III and Table IV).
The temperature conversion formula using the 10 MSBs of the
Temperature Value Register is
1.
Positive Temperature = ADC Code/4
2.
Negative Temperature = (ADC Code*
– 512)/4
*MSB
is removed from the
ADC Code.
INTERNAL REGISTER STRUCTURE
ADDRESS POINTER REGISTER
The Address Pointer Register is an 8-bit register that stores an
address that points to one of the six data registers. The first data
byte of every serial write operation to the AD7416/AD7417/
AD7418 is the address of one of the data registers, which is
stored in the Address Pointer Register, and selects the data
register to which subsequent data bytes are written. Only the
three LSBs of this register are used to select a data register.
Table I. Address Pointer Register
P7*
0
P6*
0
P5*
0
P4*
0
P3*
0
P2
P1
P0
Register Select
*P3
to P7 must be set to 0.
Table II. Register Addresses
P2
0
0
0
0
1
1
P1
0
0
1
1
0
0
P0
0
1
0
1
0
1
Registers
Temperature Value (Read-Only)
Config Register (Read/Write)
T
HYST
(Read/Write)
T
OTI
ADC (AD7417/AD7418 Only)
Config2 (AD7417/AD7418 Only)
The AD7417/AD7418 has seven internal registers, as shown in
Figure 6. Six of these are data registers and one is an Address
Pointer Register. The AD7416 has five internal registers (the
ADC and Config2 Registers are not applicable to the AD7416).
TEMPERATURE
VALUE
REGISTER
(READ-ONLY
ADDRESS 00h)
TEMPERATURE VALUE REGISTER (ADDRESS 00h)
The Temperature Value Register is a 16-bit, read-only register
whose 10 MSBs store the temperature reading from the ADC in
10-bit twos complement format. Bits 5 to 0 are unused.
Table III. Temperature Value Register
D15 D14
CONFIGURATION
REGISTER
(READ/WRITE
ADDRESS 01h)
D13
B7
D12
B6
D11 D10
B5
B4
D9
B3
D8
B2
D7
B1
D6
LSB
MSB B8
T
HYST
SETPOINT
REGISTER
(READ/WRITE
ADDRESS 02h)
T
OTI
SETPOINT
REGISTER
(READ/WRITE
ADDRESS 03h)
ADDRESS POINTER
REGISTER
(SELECTS DATA REGISTER
FOR READ/WRITE)
ADDRESS
CONFIG2
REGISTER
(READ/WRITE
ADDRESS 05h)
ADC
REGISTER
(READ-ONLY
ADDRESS 04h)
DATA
The temperature data format is shown in Table IV. This shows
the full theoretical range of the ADC from –128°C to +127°C,
but in practice, the temperature measurement range is limited
to the operating temperature range of the device.
Table IV. Temperature Data Format
Temperature
–128°C
–125°C
–100°C
–75°C
–50°C
–25°C
–0.25°C
0°C
+0.25°C
+10°C
+25°C
+50°C
+75°C
+100°C
+125°C
+127°C
Digital Output
10 0000 0000
10 0000 1100
10 0111 0000
10 1101 0100
11 0011 1000
11 1001 1100
11 1111 1111
00 0000 0000
00 0000 0001
00 0010 1000
00 0110 0100
00 1100 1000
01 0010 1100
01 1001 0000
01 1111 0100
01 1111 1100
SERIAL
BUS
INTERFACE
SDA
SCL
Figure 6. AD7417/AD7418 Register Structure
–10–
REV. G
AD [ ANALOG DEVICES ]
