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Data Sheet

ADT7408

Rev. A | Page 15 of 22

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/212); 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.

Table 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

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

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