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 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.
b
The LM122 operates over a temperature range of 55 C to
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.
§
125 C. An electrically identical LM322 is specified from
a
§
0 C to 70 C. The LM3905 is identical to the LM122 series
a
§
§
except that the boost and V
ADJ
able, limiting minimum timing period to 1 ms.
pin options are not avail-
Features
Y
Immune to changes in trigger voltage during timing
interval
The trigger input to the LM122 series has a threshold of
1.6V independent of supply voltage, but it is fully protected
Y
Timing periods from microseconds to hours
g
against inputs as high as 40VÐeven when using a 5V
Y
Internal logic reversal
supply. The circuitry reacts only to the rising edge of the
trigger signal, and is immune to any trigger voltage during
the timing periods.
Y
Immune to power supply ripple during the timing
interval
Y
Operates from 4.5V to 40V supplies
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
Y
g
Input protected to 40V
Y
Y
Y
Y
Floating transistor output with internal current limiting
Internal regulated reference
Timing period can be voltage controlled
TTL compatible input and output
through the V
achieved.
pin. Timing ratios of 50:1 can be easily
ADJ
Connection Diagrams
Metal Can Package
Dual-In-Line Package
Dual-In-Line Package
TL/H/7768–6
Top View
TL/H/7768–8
Top View
Order Number LM3905N
See NS Package Number N08E
Order Number LM122H
See NS Package Number H10C
TL/H/7768–7
Top View
Order Number LM322N
See NS Package Number N14A
C
1995 National Semiconductor Corporation
TL/H/7768
RRD-B30M115/Printed in U. S. A.
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