ADT7420UCPZ-R2 datasheet(12/24 Pages) AD

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ADT7420

Preliminary Technical Data

Rev. PrA | Page 12 of 2

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

stored in the TCRIT setpoint register and the THIGH setpoint

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

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.

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