6.

Block diagram

  

 

VCC

 

 

LM75B

 

BIAS

REFERENCE

 

POINTER

REGISTER

 

CONFIGURATION

REGISTER

 

 

BAND GAP

TEMP SENSOR

OSCILLATOR

POWER-ON

RESET

 

11-BIT SIGMA-

DELTA A-to-D

CONVERTER

 

COUNTER

TIMER

COMPARATOR/

INTERRUPT

TEMPERATURE

REGISTER

 

TOS

REGISTER

 

THYST

REGISTER

 

OS

 

 

LOGIC CONTROL AND INTERFACE

 

 

A2

A1 A0

 

SCL

 

SDA

 

GND

002aad453

 

Fig 1.

Block diagram of LM75B

 

 

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5.

General description

 

The LM75B is a temperature-to-digital converter using an on-chip band gap

temperature sensor and Sigma-Delta A-to-D conversion technique with an over

temperature detection output. The

LM75B

contains a number of data registers:

Configuration register (Conf) to store the device settings such as device operation mode,

OS operation mode, OS polarity and OS fault queue as described in Section 7 “Functional

description”; temperature register (Temp) to store the digital temp reading, and set-point

registers (Tos and Thyst) to store programmable over temperature shutdown and

hysteresis limits, that can be communicated by a controller via the 2-wire serial I2C-bus

interface. The device also includes an open-drain output (OS) which becomes active when

the temperature exceeds the programmed limits. There are three selectable logic address

pins so that eight devices can be connected on the same bus without address conflict.

The LM75B can be configured for different operation conditions. It can be set in

normal mode to periodically monitor the ambient temperature, or in shutdown mode to

minimize power consumption. The OS output operates in either of two selectable modes:

OS comparator mode or OS interrupt mode. Its active state can be selected as either

HIGH or LOW. The fault queue that defines the number of consecutive faults in order to

activate the OS output is programmable as well as the set-point limits.

The temperature register always stores an 11-bit two’s complement data giving a

temperature resolution of 0.125

C. This high temperature resolution is particularly useful

in applications of measuring precisely the thermal drift or runaway. When the LM75B is

accessed the conversion in process is not interrupted (that is, the I2C-bus section is totally

independent of the Sigma-Delta converter section) and accessing the LM75B continuously

without waiting at least one conversion time between communications will

not prevent the device from updating the Temp register with a new conversion result. The

new conversion result will be available immediately after the Temp register is updated.

The LM75B powers up in the normal operation mode with the OS in comparator

mode, temperature threshold of 80

C and hysteresis of 75 C, so that it can be used

as a stand-alone thermostat with those pre-defined temperature set points.

UMW

LM75B