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AD7418ARUZ Datasheet(PDF) 10 Page - Analog Devices

Part No. AD7418ARUZ
Description  10-Bit Digital Temperature Sensor (AD7416) and Single/Four-Channel ADC (AD7417/AD7418)
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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AD7418ARUZ Datasheet(HTML) 10 Page - Analog Devices

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REV. G
–10–
AD7416/AD7417/AD7418
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
*
P6
*
P5
*
P4
*
P3
*
P2
P1
P0
00
00
0
Register Select
*P3 to P7 must be set to 0.
Table II. Register Addresses
P2
P1
P0
Registers
0
00Temperature Value (Read-Only)
0
01Config Register (Read/Write)
0
10THYST (Read/Write)
0
11TOTI
1
00
ADC (AD7417/AD7418 Only)
1
01Config2 (AD7417/AD7418 Only)
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
D13
D12
D11
D10
D9
D8
D7
D6
MSB B8
B7
B6
B5
B4
B3
B2
B1
LSB
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
Digital Output
–128
°C
10 0000 0000
–125
°C
10 0000 1100
–100
°C
10 0111 0000
–75
°C
10 1101 0100
–50
°C
11 0011 1000
–25
°C
11 1001 1100
–0.25
°C
11 1111 1111
0
°C
00 0000 0000
+0.25
°C
00 0000 0001
+10
°C
00 0010 1000
+25
°C
00 0110 0100
+50
°C
00 1100 1000
+75
°C
01 0010 1100
+100
°C
01 1001 0000
+125
°C
01 1111 0100
+127
°C
01 1111 1100
Figure 5 shows the method the AD7416/AD7417/AD7418 uses
to measure the device temperature. To measure VBE, 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
VBE.
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
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).
THYST SETPOINT
REGISTER
(READ/WRITE
ADDRESS 02h)
CONFIGURATION
REGISTER
(READ/WRITE
ADDRESS 01h)
TOTI SETPOINT
REGISTER
(READ/WRITE
ADDRESS 03h)
SERIAL
BUS
INTERFACE
SCL
TEMPERATURE
VALUE
REGISTER
(READ-ONLY
ADDRESS 00h)
ADDRESS POINTER
REGISTER
(SELECTS DATA REGISTER
FOR READ/WRITE)
ADDRESS
DATA
CONFIG2
REGISTER
(READ/WRITE
ADDRESS 05h)
ADC
REGISTER
(READ-ONLY
ADDRESS 04h)
SDA
Figure 6. AD7417/AD7418 Register Structure


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