Datasheet

ADT7420 Data Sheet
Rev. 0 | Page 12 of 24
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 T
CRIT
setpoint register and the T
HIGH
setpoint register. It is also com-
pared with the low temperature limit stored in the T
LOW
setpoint
register.
Temperature data in the temperature value register, the T
CRIT
setpoint register, the T
HIGH
setpoint register, and the T
LOW
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 conversion result and
are flag bits for T
CRIT
, T
HIGH
, and T
LOW
. 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
Temperature
Digital Output
(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
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.