TLH7768

February 1995

LM122LM322LM3905 Precision Timers

General Description

The LM122 series are precision timers that offer great ver-

satility with high accuracy They operate with unregulated

supplies from 45V to 40V while maintaining constant timing

periods from microseconds to hours Internal logic and reg-

ulator circuits complement the basic timing function

enabling the LM122 series to operate in many different ap-

plications with a minimum of external components

The output of the timer is a floating transistor with built in

current limiting It can drive either ground referred or supply

referred loads up to 40V and 50 mA The floating nature of

this output makes it ideal for interfacing lamp or relay driv-

ing and signal conditioning where an open collector or emit-

ter is required A ‘‘logic reverse’’ circuit can be programmed

by the user to make the output transistor either ‘‘on’’ or

‘‘off’’ during the timing period

The trigger input to the LM122 series has a threshold of

16V independent of supply voltage but it is fully protected

supply The circuitry reacts only to the rising edge of the

trigger signal and is immune to any trigger voltage during

the timing periods

An internal 315V regulator is included in the timer to reject

supply voltage changes and to provide the user with a con-

venient reference for applications other than a basic timer

External loads up to 5 mA can be driven by the regulator An

internal 2V divider between the reference and ground sets

the timing period to 1 RC The timing period can be voltage

controlled by driving this divider with an external source

achieved

The comparator used in the LM122 utilizes high gain PNP

input transistors to achieve 300 pA typical input bias current

over a common mode range of 0V to 3V A boost terminal

allows the user to increase comparator operating current for

timing periods less than 1 ms This lets the timer operate

over a 3 ms to multi-hour timing range with excellent repeat-

ability

a

125 C An electrically identical LM322 is specified from

able limiting minimum timing period to 1 ms

Features

Y

Immune to changes in trigger voltage during timing

interval

Y

Timing periods from microseconds to hours

Y

Internal logic reversal

Y

Immune to power supply ripple during the timing

interval

Y

Operates from 45V to 40V supplies

Y

Y

Floating transistor output with internal current limiting

Y

Internal regulated reference

Y

Timing period can be voltage controlled

Y

TTL compatible input and output

Connection Diagrams

Metal Can Package

TLH7768 – 6

Top View

Order Number LM122H

See NS Package Number H10C

Dual-In-Line Package

TLH7768 – 7

Top View

Order Number LM322N

See NS Package Number N14A

Dual-In-Line Package

TLH7768 – 8

Top View

Order Number LM3905N

See NS Package Number N08E

C1995 National Semiconductor Corporation

RRD-B30M115Printed in U S A