ELM331

Elm Electronics – Circuits for the Hobbyist

< http://www.elmelectronics.com/ >

Connection Diagram

PDIP and SOIC

(top view)

1

2

3

4

8

7

6

5

Solid State Thermostat

The

ELM331

is

a

complete

temperature

measurement and control system in an 8 pin

package.

This integrated circuit is designed to compare

two resistances and drive an output pin depending

on the relative value of each. Typically, one of the

resistors will be an NTC thermistor, and the other

one will be a temperature independent resistor

(whether fixed or variable). When the magnitude of

the resistance connected to pin 2 exceeds the value

of the resistance connected to pin 3, the output pin

will be driven to a high state. Hysteresis maintains

the output in that state until the relative values differ

by approximately 8% (or typically 2°C for a 10K

Ω

thermistor).

To reduce the possibility of sporadic outputs, a

condition must exist for three successive cycles, or 6

seconds, before the output pin can change state.

• Low power CMOS design - typically 1mA at 5V

• Wide supply range - 3.0 to 5.5 volt operation

• Built-in proportional hysteresis

• Measurement in progress output

• Time delay on operate improves noise immunity

• Internal pullup resistor on the reset input

• High current drive outputs - up to 25 mA

• Primary thermostat in temperature control

systems

• Staging control for auxiliary heating or cooling

installations

• Under or over temperature alarms

2

3

4

6

7

Analog to

Digital

Converter

5

Control

Watchdog

Timer

Cap

MIP

Out

reset

3 Consecutive

Measurements

Measurement in Progress (busy)

Overrange

Out

MIP

reset

Description

Applications

Block Diagram

1 of 4

Features

ELM331DSB