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LM3914N
Dot/Bar Display Driver
LM3914
Dot/Bar Display Driver
General DescriptionThe LM3914isa monolithic integrated circuit that senses
analog voltage levels and drives10 LEDs, providinga linear
analog display.A singlepin changesthe display froma mov-
ingdottoabar graph. Current drivetothe LEDsis regulated
and programmable, eliminating the needfor resistors. This
featureis one that allows operationofthe whole system from
less than3V.
The circuit containsits own adjustable reference and accu-
rate 10-step voltage divider. The low-bias-current input
buffer accepts signals downto ground,orV−,yet needsno
protection against inputsof 35V aboveor below ground. The
buffer drives10 individual comparators referencedto the
precision divider. Indication non-linearity can thusbe held
typicallyto 1⁄2%, even overa wide temperature range.
Versatility was designed into the LM3914so that controller,
visual alarm, and expanded scale functions are easily addedtothe display system. The circuit can drive LEDsof many
colors,or low-current incandescent lamps. Many LM3914s
canbe “chained”to form displaysof20to over 100 seg-
ments. Both endsof the voltage dividerare externally avail-
ableso that2 drivers canbe made intoa zero-center meter.
The LM3914is very easyto applyasan analog meter circuit. 1.2V full-scale meter requires only1 resistor anda singleto 15V supplyin additiontothe10 display LEDs.Ifthe1
resistorisa pot,it becomesthe LED brightness control. The
simplified block diagram illustrates this extremely simpleex-
ternal circuitry.
Wheninthedot mode, thereisa small amountof overlapor
“fade” (about1 mV) between segments. This assures thatat timewillall LEDsbe “OFF”, and thus any ambiguous dis-
playis avoided. Various novel displays are possible.
Muchof the display flexibility derives from the fact thatall
outputs are individual,DC regulated currents. Various effects
canbe achievedby modulating these currents. The indi-
vidual outputs can drivea transistoras wellasa LEDatthe
same time,so controller functions including “staging” control
canbe performed. The LM3914 can alsoactasa program-
mer,or sequencer.
The LM3914is ratedfor operation from 0˚Cto +70˚C. The
LM3914N-1is availableinan 18-lead molded(N) package.
The following typical application illustrates adjustingof the
referencetoa desired value, and proper groundingfor accu-
rate operation, and avoiding oscillations.
Features Drives LEDs, LCDsor vacuum fluorescents Baror dot display mode externally selectableby user Expandableto displaysof 100 steps Internal voltage reference from 1.2Vto 12V Operates with single supplyof less than3V Inputs operate downto ground Output current programmable from2 mAto30 mA No multiplex switchingor interaction between outputs Input withstands ±35V without damageor false outputs LED driver outputsare current regulated,
open-collectors Outputs can interface with TTLor CMOS logic The internal 10-step divideris floating and canbe
referencedtoa wide rangeof voltages
January 2000
LM3914
Dot/Bar
Display
Driver
