LM75B_2

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 02 — 9 December 2008

9 of 29

NXP Semiconductors

LM75B

Digital temperature sensor and thermal watchdog

For 9-bit Temp data application in replacing the industry standard LM75, just use only

9 MSB bits of the two bytes and disregard 7 LSB of the LSByte. The 9-bit Temp data with

0.5

°C resolution of the LM75B is defined exactly in the same way as for the standard

LM75 and it is here similar to the Tos and Thyst registers.

The only MSByte of the temperature can also be read with the use of a one-byte reading

command. Then the temperature resolution will be 1.00

°C instead.

7.4.4 Overtemperature shutdown threshold (Tos) and hysteresis (Thyst) registers

These two registers, are write/read registers, and also called set-point registers. They are

used to store the user-defined temperature limits, called overtemperature shutdown

At the end of each conversion the Temp data will be compared with the data stored in

these two registers in order to set the state of the device OS output; see Section 7.1.

Each of the set-point registers contains two 8-bit data bytes consisting of one MSByte and

one LSByte the same as register Temp. However, only 9 bits of the two bytes are used to

store the set-point data in 2’s complement format with the resolution of 0.5

°C. Table 10

and Table 11 show the bit arrangement of the Tos data and Thyst data in the data bytes.

Notice that because only 9-bit data are used in the set-point registers, the device uses

only the 9 MSB of the Temp data for data comparison.

When a set-point register is read, all 16 bits are provided to the bus and must be collected

by the controller to complete the bus operation. However, only the 9 most significant bits

should be used and the 7 LSB of the LSByte are equal to zero and should be ignored.

Table 12 shows examples of the limit data and value.

111 0011 1000

738

−200

−25.000 °C

110 0100 1001

649

−439

−54.875 °C

110 0100 1000

648

−440

−55.000 °C

Table 9.

11-bit binary

(2’s complement)

Hexadecimal value

Decimal value

Value

Table 10.

Tos register

MSByte

LSByte

7654321076543210

D8

D7

D6

D5

D4

D3

D2

D1

D0

XXXXXXX

Table 11.

Thyst register

MSByte

LSByte

7654321076543210

D8

D7

D6

D5

D4

D3

D2

D1

D0

XXXXXXX