EVAL-ADT7X20EBZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-ADT7X20EBZ' PDF : 24 Pages View PDF
ADT7420
TEMPERATURE DATA FORMAT
One LSB of the ADC corresponds to 0.0625°C in 13-bit mode
or 0.0078°C in 16-bit mode. The ADC can theoretically
measure a temperature range of 255°C, but the ADT7420 is
guaranteed to measure a low value temperature limit of −40°C
to a high value temperature limit of +150°C. The temperature
measurement result is stored in the 16-bit temperature value
register and is compared with the high temperature limits
stored in the TCRIT setpoint register and the THIGH setpoint
register. It is also compared with the low temperature limit
stored in the TLOW setpoint register.
Temperature data in the temperature value register, the TCRIT
setpoint register, the THIGH setpoint register, and the TLOW
setpoint register are represented by a 13-bit twos complement
word. The MSB is the temperature sign bit. The three LSBs, Bit 0
to Bit 2, on power-up, are not part of the temperature conver-
sion result and are flag bits for TCRIT, THIGH, and TLOW. Table 5
shows the 13-bit temperature data format without Bit 0 to Bit 2.
The number of bits in the temperature data-word can be extended
to 16 bits, twos complement, by setting Bit 7 to 1 in the confi-
guration register (Register Address 0x03). When using a 16-bit
temperature data value, Bit 0 to Bit 2 are not used as flag bits
and are, instead, the LSB bits of the temperature value. The
power-on default setting has a 13-bit temperature data value.
Reading back the temperature from the temperature value register
requires a 2-byte read. Designers that use a 9-bit temperature
data format can still use the ADT7420 by ignoring the last four
LSBs of the 13-bit temperature value. These four LSBs are Bit 6
to Bit 3 in Table 5.
Table 5. 13-Bit Temperature Data Format
Digital Output
Temperature (Binary) Bits[15:3]
Digital Output (Hex)
−40°C
1 1101 1000 0000
0x1D80
−25°C
1 1110 0111 0000
0x1E70
−0.0625°C
1 1111 1111 1111
0x1FFF
0°C
0 0000 0000 0000
0x000
+0.0625°C
0 0000 0000 0001
0x001
+25°C
0 0001 1001 0000
0x190
+105°C
0 0110 1001 0000
0x690
+125°C
0 0111 1101 0000
0x7D0
+150°C
0 1001 0110 0000
0x960
Preliminary Technical Data
TEMPERATURE CONVERSION FORMULAS
16-Bit Temperature Data Format
Positive Temperature = ADC Code (dec)/128
Negative Temperature = (ADC Code (dec) – 65,536)/128
where ADC Code uses all 16 bits of the data byte, including the
sign bit.
Negative Temperature = (ADC Code (dec) – 32,768)/128
where Bit 15 (sign bit) is removed from the ADC code.
13-Bit Temperature Data Format
Positive Temperature = ADC Code (dec)/16
Negative Temperature = (ADC Code (dec) − 8192)/16
where ADC Code uses the first 13 MSBs of the data byte,
including the sign bit.
Negative Temperature = (ADC Code (dec) – 4096)/16
where Bit 15 (sign bit) is removed from the ADC code.
10-Bit Temperature Data Format
Positive Temperature = ADC Code (dec)/2
Negative Temperature = (ADC Code (dec) − 1024)/2
where ADC Code uses all 10 bits of the data byte, including the
sign bit.
Negative Temperature = (ADC Code (dec) − 512)/2
where Bit 9 (sign bit) is removed from the ADC code.
9-Bit Temperature Data Format
Positive Temperature = ADC Code (dec)
Negative Temperature = ADC Code (dec) − 512
where ADC Code uses all nine bits of the data byte, including
the sign bit.
Negative Temperature = ADC Code (dec) − 256
where Bit 8 (sign bit) is removed from the ADC code.
Rev. PrA | Page 12 of 2
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