LM122 LM322 LM3905 Precision Timers
February 1995
LM122 LM322 LM3905 Precision Timers
General Description
The LM122 series are precision timers that offer great ver-
satility with high accuracy They operate with unregulated
supplies from 4 5V 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 鈥樷€榣ogic reverse鈥欌€?circuit can be programmed
by the user to make the output transistor either 鈥樷€榦n鈥欌€?or
鈥樷€榦ff鈥欌€?during the timing period
The
trigger
input to the LM122 series has a threshold of
1 6V independent of supply voltage but it is fully protected
against inputs as high as
g
40V even when using a 5V
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 3 15V 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
through the
V
ADJ
pin Timing ratios of 50 1 can be easily
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
The LM122 operates over a temperature range of
b
55 C to
a
125 C An electrically identical LM322 is specified from
0 C to
a
70 C The LM3905 is identical to the LM122 series
except that the
boost
and
V
ADJ
pin options are not avail-
able limiting minimum timing period to 1 ms
Features
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Immune to changes in trigger voltage during timing
interval
Timing periods from microseconds to hours
Internal logic reversal
Immune to power supply ripple during the timing
interval
Operates from 4 5V to 40V supplies
Input protected to
g
40V
Floating transistor output with internal current limiting
Internal regulated reference
Timing period can be voltage controlled
TTL compatible input and output
Connection Diagrams
Metal Can Package
Dual-In-Line Package
Dual-In-Line Package
TL H 7768 鈥?
Top View
Order Number LM122H
See NS Package Number H10C
TL H 7768 鈥?8
TL H 7768 鈥?7
Top View
Order Number LM322N
See NS Package Number N14A
Top View
Order Number LM3905N
See NS Package Number N08E
C
1995 National Semiconductor Corporation
TL H 7768
RRD-B30M115 Printed in U S A
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