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LM3905N
Precision Timers
TL/H/7768
LM122/LM322/LM3905
Precision
Timers
February 1995
LM122/LM322/LM3905 Precision Timers
General Description
The LM122 seriesare precision timersthat offer greatver-
satility with high accuracy. They operate with unregulated
supplies from 4.5Vto40V while maintaining constant timing
periods from microsecondsto hours. Internal logicandreg-
ulator circuits complement the basic timing function
enablingthe LM122 seriesto operatein many differentap-
plicationswitha minimumof external components.
The outputofthe timerisa floating transistor with builtin
current limiting.Itcan drive either ground referredor supply
referred loadsupto 40Vand50mA. The floating natureof
this output makesit idealfor interfacing, lampor relay driv-
ing, andsignal conditioning wherean opencollectoror emit-
teris required.A ‘‘logic reverse’’ circuitcanbe programmedthe userto makethe output transistor either ‘‘on’’or
‘‘off’’ duringthe timing period.
The trigger inputtothe LM122 series hasa thresholdof
1.6V independentof supply voltage,butitisfully protected
against inputsas highas g40VÐeven when usinga5V
supply. The circuitry reacts onlytothe rising edgeofthe
trigger signal,andis immunetoany trigger voltage during
the timing periods. internal 3.15V regulatoris includedinthe timerto reject
supply voltage changesandto providethe userwitha con-
venient referencefor applications other thana basic timer.
External loadsupto5 mAcanbe drivenbythe regulator.An
internal2V divider betweenthe reference and ground sets
the timing periodto1RC. The timing periodcanbe voltage
controlledby driving this divider withan external source
throughthe VADJpin. Timing ratiosof 50:1canbe easily
achieved.
The comparator usedinthe LM122 utilizes high gain PNP
input transistorsto achieve300pA typical input bias current
overa common mode rangeof0Vto3V.A boost terminal
allowsthe userto increase comparatoroperating currentfor
timing periods less than1ms. Thisletsthe timer operate
overa3msto multi-hour timing range with excellent repeat-
ability.
The LM122 operates over atemperature rangeof b55§Cto
a125§C.An electrically identical LM322is specified from
0§Cto a70§C.The LM3905is identicaltothe LM122 series
except thatthe boost and VADJpin optionsarenot avail-
able, limiting minimum timing periodto1ms.
Features Immuneto changesin trigger voltage during timing
interval Timing periods from microsecondsto hours Internal logic reversal Immuneto power supply ripple duringthe timing
interval Operates from 4.5Vto 40V supplies Input protectedto g40V Floating transistor output with internal current limiting Internal regulated reference Timing periodcanbe voltage controlled TTL compatible inputand output
Connection Diagrams
Metal Can Package
TL/H/7768–6
Top View
Order Number LM122H
SeeNS Package Number H10C
Dual-In-Line Package
TL/H/7768–7
Top View
Order Number LM322N
SeeNS PackageNumberN14A
Dual-In-LinePackage
TL/H/7768–8
TopView
Order Number LM3905N
SeeNS Package Number N08E
C1995National SemiconductorCorporation RRD-B30M115/PrintedinU.S.A.
