Datasheet

ADT7408
Rev. 0 | Page 15 of 24
TEMPERATURE DATA FORMAT
The values used in the temperature register and three
temperature trip point registers are in twos complement format.
The temperature register has a 12-bit resolution with 256°C
range with 1 LSB = 0.0625°C (256°C/2
12
); see Table 10. The
temperature data in the three temperature trip point registers
(alarm upper, alarm lower, and critical) is a 10-bit format with
256°C range with 1 LSB = 0.25°C (see the bit maps in the
Alarm
Temperature Lower Boundary Trip Register (Read/Write)
section, the
Critical Temperature Trip Register (Read/Write)
section, and the
Temperature Value Register (Read Only) section.)
Bit D12 in all these registers represents the sign bit such that
0 = positive temperature and 1 = negative temperature. In twos
complement format, the data bits are inverted and add 1 if
Bit D12 (the sign bit) is negative.
Temperature Conversion Formulas
12-Bit Temperature Data Format
Positive Temperature = ADC Code(d)/16 (1)
Negative Temperature = (ADC Code(d) − 4096)/16 (2)
where d is the 12-bit digital output in decimal.
Note that Bit D12 (the sign bit) is not included in the ADC
code, but the sign is inserted in the final result.
Tabl e 10 tabulates some temperature results vs. digital outputs.
10-Bit Temperature Data Format
Positive Temperature = ADC Code(d)/4 (3)
Negative Temperature = (ADC Code(d) − 1024)/4 (4)
Similarly, Bit D12 (the sign bit) is not included in the ADC
code, but the sign is inserted in the final result. This ADC code
contains DB2 to DB11. DB0 to DB1 are not in this calculation.
Although one LSB of the ADC corresponds to 0.0625°C, the
ADC can theoretically measure a temperature range of 255°C
(−128°C to +127°C ). The ADT7408 is guaranteed to measure
a low value temperature limit of −55°C to a high value temperature
limit of +125°C.
Reading back the temperature from the temperature value
register requires a 2-byte read.
Designers accustomed to using a 9-bit temperature data format
can still use the ADT7408 by ignoring the last three LSBs of the
12-bit temperature value.
Table 10. 12-Bit Temperature Data Format
Digital Output (Binary)
D12 to D0
Digital Output
(Hex)
Temperature
1 1100 1001 0000 C90 −55°C
1 1100 1110 0000 CE0 −50°C
1 1110 0110 1111 E6F −25°C
1 1111 1111 1111 FFF −0.0625°C
0 0000 0000 0000 000 0°C
0 0000 0000 0001 0x001 +0.0625°C
0 0000 1010 0000 0x0A0 +10°C
0 0001 1001 0000 0x190 +25°C
0 0011 0010 0000 0x320 +50°C
0 0100 1011 0000 0x4B0 +75°C
0 0110 0100 0000 0x640 +100°C
0 0111 1101 0000 0x7D0 +125°C