7

6

5

A0

A1

A2

Temperature

Threshold

Silicon Bandgap

Temperature

Sensor

Ð

1-Bit

D/A

10-Bit

Digital

Decimation

Filter

9-Bit Sigma-Delta ADC

Configuration

Register

TOS Set Point

Register

Pointer

Register

THYST Set

Point Register

Set Point

Comparator

3

O.S.

Reset

1

2

SDA

SCL

Two-Wire Interface

4

8

+VS

GND

Product ID

Register

LM75A

SNOS808P – JANUARY 2000 – REVISED DECEMBER 2014

www.ti.com

7 Detailed Description

7.1 Overview

The LM75A temperature sensor incorporates a band-gap type temperature sensor and 9-bit ADC (sigma-delta

ADC). The temperature data output of the LM75A is available at all times via the I2C bus. If a conversion is in

progress, it will be stopped and restarted after the read. A digital comparator is also incorporated that compares

a series of readings, the number of which is user-selectable, to user-programmable setpoint and hysteresis

values. The comparator trips the O.S. output line, which is programmable for mode and polarity. The LM75A has

an integrated low-pass filter on both the SDA and the SCL line. These filters increase communications reliability

in noisy environments.

The LM75A also has a bus fault timeout feature. If the SDA line is held low for longer than tTIMEOUT (see

specification) the LM75A will reset to the IDLE state (SDA set to high impedance) and wait for a new start

condition. The TIMEOUT feature is not functional in Shutdown Mode.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Digital Temperature Sensor

The LM75A is an industry-standard digital temperature sensor with an integrated sigma-delta ADC and I2C

interface. The LM75A provides 9-bit digital temperature readings with an accuracy of ±2°C from –25°C to 100°C

and ±3°C over –55°C to 125°C.

The LM75A operates with a single supply from +2.7 V to +5.5 V. Communication is accomplished over a 2-wire

interface which operates up to 400kHz. The LM75A has three address pins, allowing up to eight LM75A devices

to operate on the same 2-wire bus. The LM75A has a dedicated over-temperature output (O.S.) with

programmable limit and hysteresis. This output has programmable fault tolerance, which allows the user to

define the number of consecutive error conditions that must occur before O.S. is activated.

7.4 Device Functional Modes

In Comparator mode the O.S. Output behaves like a thermostat. The output becomes active when temperature

exceeds the TOS limit, and leaves the active state when the temperature drops below the THYST limit. In this mode

the O.S. output can be used to turn a cooling fan on, initiate an emergency system shutdown, or reduce system

clock speed. Shutdown mode does not reset O.S. state in a comparator mode.

In Interrupt mode exceeding TOS also makes O.S. active but O.S. will remain active indefinitely until reset by

reading any register via the I2C interface. Once O.S. has been activated by crossing TOS, then reset, it can be

activated again only by Temperature going below THYST. Again, it will remain active indefinitely until being reset

by a read. Placing the LM75A in shutdown mode also resets the O.S. Output.

10

Submit Documentation Feedback

Copyright © 2000–2014, Texas Instruments Incorporated

Product Folder Links: LM75A