LM75B_2

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 02 — 9 December 2008

4 of 29

NXP Semiconductors

LM75B

Digital temperature sensor and thermal watchdog

6.2 Pin description

7.

Functional description

7.1 General operation

The LM75B uses the on-chip band gap sensor to measure the device temperature with

the resolution of 0.125

°C and stores the 11-bit 2's complement digital data, resulted from

11-bit A-to-D conversion, into the device Temp register. This Temp register can be read at

conversion in progress during the read operation.

The device can be set to operate in either mode: normal or shutdown. In normal operation

mode, the temp-to-digital conversion is executed every 100 ms and the Temp register is

to complete a temperature-to-data conversion and then becomes idle for the time

remaining in the period. This feature is implemented to significantly reduce the device

power dissipation. In shutdown mode, the device becomes idle, data conversion is

interface is still active and register write/read operation can be performed. The device

operation mode is controllable by programming bit B0 of the configuration register. The

temperature conversion is initiated when the device is powered-up or put back into normal

mode from shutdown.

In addition, at the end of each conversion in normal mode, the temperature data (or Temp)

in the Temp register is automatically compared with the overtemperature shutdown

stored in the Thyst register, in order to set the state of the device OS output accordingly.

The device Tos and Thyst registers are write/read capable, and both operate with 9-bit

2's complement digital data. To match with this 9-bit operation, the Temp register uses

only the 9 MSB bits of its 11-bit data for the comparison.

The way that the OS output responds to the comparison operation depends upon the OS

operation mode selected by configuration bit B1, and the user-defined fault queue defined

by configuration bits B3 and B4.

Table 2.

Pin description

Symbol

Pin

Description

SDA

1

SCL

2

OS

3

Overtemp Shutdown output; open-drain.

GND

4

Ground. To be connected to the system ground.

A2

5

Digital input. User-defined address bit 2.

A1

6

Digital input. User-defined address bit 1.

A0

7

Digital input. User-defined address bit 0.

8

Power supply.