LM81 datasheet(18/32 Pages) NSC

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Functional Description (Continued)

8.0 TEMPERATURE MEASUREMENT SYSTEM

The LM81 temperature sensor and ADC produce 9-bit or

12-bit two’s-complement temperature data. A digital com-

parator

compares

the

temperature

data

the

user-programmable High, Low, Critical setpoints and Hyster-

esis values.

8.1 Temperature Data Format

Temperature data can be read from the Temperature, T

HIGH

setpoint, T

HIHYST setpoint, TLOW setpoint, TC setpoint and

HYST Offset registers; and written to the THIGH setpoint,

HIHYST,TLOW setpoint, T_CRIT setpoint and THYST offset

registers. T

HIGH setpoint, TLOW setpoint, T_CRIT setpoint

temperature data is represented by an 8-bit, two’s comple-

ment word with an LSB (Least Significant Bit) equal to 1˚C:

Temperature

Digital Output

Binary

Hex

+125˚C

0111 1101

7Dh

+25˚C

0001 1001

19h

+1.0˚C

0000 0001

01h

+0˚C

0000 0000

00h

−1.0˚C

1111 1111

FFh

−25˚C

1110 0111

E7h

−55˚C

1100 1001

C9h

By default Temperature Register data is represented by a

9-bit two’s complement digital word with the LSB having a

resolution of 0.5˚C:

Temperature

Digital Output

Binary

Hex

+125˚C

0 1111 1010

0 FAh

+25˚C

0 0011 0010

0 32h

+1.5˚C

0 0000 0011

0 03h

+0˚C

0 0000 0000

0 00h

−0.5˚C

1 1111 1111

1 FFh

−25˚C

1 1100 1110

1 CEh

−55˚C

1 1001 0010

1 92h

In the extended mode temperature Register data can also be

represented by a 12-bit two’s complement digital word with

an LSB of 0.0625˚C:

Temperature

Digital Output

Binary

Hex

+125˚C

0111 1100 0000

7 D0h

+25˚C

0001 1001 0000

1 90h

+1.0˚C

0000 0001 0000

0 10h

+0.0625˚C

0000 0000 0001

0 01h

0˚C

0000 0000 0000

0 00h

−0.0625˚C

1111 1111 1111

F FFh

−1.0˚C

1111 1111 0000

F F0h

−25˚C

1110 0111 0000

E 70h

−55˚C

1100 1001 0000

C 90h

HYST Offset temperature data is represented by a 3-bit word

with an LSB (Least Significant Bit) equal to 1˚C.

DS100072-24

(Non-Linear Scale for Clarity)

FIGURE 9. 9-bit Temperature-to-Digital Transfer

Function

DS100072-27

(Non-Linear Scale for Clarity)

FIGURE 10. 12-bit Temperature-to-Digital Transfer

Function

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