GND

OS

HYST

REF

TEMP

SENSOR

+

-

V+

V

+

LM26__C

HYST

GND

HYST

REF

TEMP

SENSOR

+

-

HYST

LM26__B

V

+

US

GND

HYST

OS

REF

TEMP

SENSOR

+

-

HYST

LM26__A

V

+

LM26

www.ti.com

SNIS115S – MAY 2001 – REVISED SEPTEMBER 2015

8 Detailed Description

8.1 Overview

The LM26 is a factory preset thermostat (temperature switch) that includes an integrated temperature sensor,

reference voltage, DAC and comparator. The LM26 can be factory programmed to have a trip point anywhere in

the range of

−55°C to +120°C. The output functionality can also be changed during the manufacturing process,

as described in the functional block diagrams. Available options include:

•

OS: active low, open drain that indicates an over temperature shutdown event (most common)

•

US: active low, open-drain that indicates an under temperature shutdown event

•

OS: active high, push-pull that indicates an over temperature shutdown event

•

US: active high, push-pull that indicates an under temperature shutdown event

that the LM26 is reading by monitoring with an ADC. It has a negative temperature coefficient (NTC) of

approximately -10mV/°C. This pin also allows after assembly PCB testing (see section After Assembly PCB

Testing for more details).

The comparator hysteresis is selectable by the state of the HYST. Two values are available 10°C or 2°C.

Comparator hysteresis is essential, as it prevents comparator output chattering when the temperature is at the

comparator threshold set point (REF as shown in the functional block diagrams). Once the comparator trips the

hysteresis function changes the comparator threshold (REF) level such that the output remains locked in the

active state. The threshold is changed by either 10°C or 2°C as programmed by the state of the HYST pin.

8.2 Functional Block Diagrams

Figure 2. LM26-_ _A Output Pin Block Diagram

Figure 3. LM26-_ _B Output Pin Block Diagram

Figure 4. LM26-_ _C Output Pin Block Diagram

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