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

register.

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

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.