EVAL-AD7416/7/8EBZ Analog Devices Inc, EVAL-AD7416/7/8EBZ Datasheet - Page 12

• Manufacturer Part Number: EVAL-AD7416/7/8EBZ
• Description: EVALUATION BOARD I.C.
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD7416/7/8EBZ

• Sensor Type: Temperature
• Sensing Range: -40°C ~ 125°C
• Interface: I²C
• Voltage - Supply: 2.7 V ~ 5.5 V
• Embedded: No
• Utilized Ic / Part: AD7416, AD7417, AD7418
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Sensitivity: -
• Lead Free Status / Rohs Status: Supplier Unconfirmed

AD7416/AD7417/AD7418
An external 2.5 V reference can be connected to the REF
This has the effect of shutting down the on-chip reference
circuitry.
TEMPERATURE MEASUREMENT
A common method of measuring temperature is to exploit the
negative temperature coefficient of a diode, or the base-emitter
voltage of a transistor, operated at a constant current. Unfortu-
nately, this technique requires calibration to null out the effect
of the absolute value of V
The technique used in the AD7416/AD7417/AD7418 is to
measure the current change in V
at two different currents.
This is given by
where:
K is Boltzmann’s constant.
q is the charge on the electron (1.6 × 10
T is the absolute temperature in Kelvins.
N is the ratio of the two currents.
Figure 12 shows the method the AD7416/AD7417/AD7418 use
to measure the device temperature. To measure ΔV
sensor (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 ΔV
to give a temperature output in 10-bit twos complement form.
TRANSISTOR
SENSING
Δ
V
BE
=
Figure 12. Temperature Measurement Technique
KT
1.2V
I
/ ×
q
Figure 11. On-Chip Reference
n 1
( )
N
BE
BE
SENSING
TRANSISTOR
, which varies from device to device.
. This voltage is measured by the ADC
SW1
N × I
REF
BE
IN
26kΩ
24kΩ
when the device is operated
1.2V
−19
V
DD
Coulombs).
2.5V
BE
EXTERNAL
REFERENCE
DETECT
BUFFER
, the
TO ADC
V
V
IN
OUT+
OUT–
pin.
Rev. I | Page 12 of 24
The temperature resolution of the ADC is 0.25°C, which corres-
ponds 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 (0x00) as a 16-bit word. The 10 MSBs
of this word store the temperature measurement (see Table 9
and Table 10).
The temperature conversion formulas using the 10 MSBs of the
temperature value register are
The MSB is removed from ADC Code in Equation 2.
INTERNAL REGISTER STRUCTURE
The AD7417/AD7418 have seven internal registers, as shown in
Figure 13. 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).
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 the address pointer register are used to select a
data register.
Table 7. Address Pointer Register
P7
0
1
P3 to P7 must be set to 0.
(SELCTS DATA REGISTER
1
ADDRESS POINTER
FOR READ/WRITE)
Positive Temperature = ADC Code/4
Negative Temperature = (ADC Code − 512)/4
REGISTER
P6
0
1
Figure 13. AD7417/AD7418 Register Structure
ADDRESS
P5
0
SERIAL BUS INTERFACE
1
P4
0
1
CONFIGURATION
T
ADDRESS 0x00)
ADDRESS 0x01)
ADDRESS 0x02)
ADDRESS 0x03)
ADDRESS 0x04)
ADDRESS 0x05)
TEMPERATURE
T
HYST
(READ/WRITE
(READ/WRITE
(READ/WRITE
(READ/WRITE
P3
0
(READ-ONLY
(READ-ONLY
OTI
ADC VALUE
REGISTER
REGISTER
REGISTER
REGISTER
REGISTER
REGISTER
CONFIG2
VALUE
1
SETPOINT
SETPOINT
P2
Register select
P1
DATA
SDA
SCL
P0
(1)
(2)