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LM3911N
LM3911 Temperature Controller
TL/H/5701
LM3911
Temperature
Controller
June 1994
LM3911 Temperature Controller
General Description
The LM3911isa highly accurate temperature measurement
and/orcontrol systemforuse overa b25§Cto a85§C tem-
perature range. Fabricatedona single monolithic chip,it
includesa temperature sensor,a stable voltage reference
andan operational amplifier.
The output voltageofthe LM3911is directly proportionalto
temperaturein degrees Kelvinat10 mV/§K. Usingthe inter-
nalop amp with external resistorsany temperature scale
factoris easily obtained.By connectingtheop ampasa
comparator,the outputwill switchasthe temperature trans-
versesthe set-point makingthe device usefulasan on-off
temperature controller. active shunt regulatoris connected acrossthe power
leadsofthe LM3911to providea stable 6.8V voltage refer-
enceforthe sensing system. This allowsthe useofany
power supply voltagewith suitable external resistors.
The input bias currentislow and relatively constant with
temperature, ensuring high accuracy when high sourceim-
pedanceis used. Further,the output collector canbere-
turnedtoa voltage higherthan 6.8V allowingthe LM3911to
drive lampsand relaysuptoa 35V supply.
The LM3911 usesthe differencein emitter-base voltageof
transistors operatingat different current densitiesastheba-
sic temperature sensitive element. Sincethis outputde-
pends onlyon transistor matchingthe same reliability and
stabilityas presentop ampscanbe expected.
The LM3911is availableintwo package styles,a metalcan
TO-46andan 8-lead epoxy mini-DIP.Inthe epoxy package
all electrical connectionsare madeonone sideofthede-
vice allowingthe other4 leadstobe usedfor attachingthe
LM3911tothe temperature souce. The LM3911is ratedfor
operation overa b25§Cto a85§C temperature range.
Features Uncalibrated accuracy g10§C Internalop amp with frequency compensation Linear outputof10 mV/§K(10 mV/§C) Canbe calibratedin degrees Kelvin, Celsiusor
Fahrenheit Outputcan drive loadsupto 35V Internal stable voltage reference Low cost
Block Diagram
Typical Applications
Ground Referred
CentigradeThermometer Trimsoutinitial zener tolerance.
Set outputtoreadC
BasicTemperature Controller Outputgoes negativeon
temperature increase
RSe(Vab6.8V)kX
ProportioningTemperature
Controller
Note1:C1determinesproportioning frequencyf&1
2R4C1
Note2:R10elValalVbl b7V
0.0015A
Note3: EitherVborVacanbe ground.
TL/H/5701–1
C1995National SemiconductorCorporation RRD-B30M115/PrintedinU.S.A.
