LM3914.PDF

February 1995

LM3914 Dot/Bar Display Driver

%, even over a wide temperature range.

Versatility was designed into the LM3914 so that controller,

visual alarm, and expanded scale functions are easily added

on to the display system. The circuit can drive LEDs of many

colors, or low-current incandescent lamps. Many LM3914s

can be ``chained'' to form displays of 20 to over 100 seg-

ments. Both ends of the voltage divider are externally avail-

able so that 2 drivers can be made into a zero-center meter.

The LM3914 is very easy to apply as an analog meter cir-

cuit. A 1.2V full-scale meter requires only 1 resistor and a

single 3V to 15V supply in addition to the 10 display LEDs. If

the 1 resistor is a pot, it becomes the LED brightness con-

trol. The simplified block diagram illustrates this extremely

simple external circuitry.

When in the dot mode, there is a small amount of overlap or

``fade'' (about 1 mV) between segments. This assures that

at no time will all LEDs be ``OFF'', and thus any ambiguous

display is avoided. Various novel displays are possible.

Much of the display flexibility derives from the fact that all

outputs are individual, DC regulated currents. Various ef-

fects can be achieved by modulating these currents. The

individual outputs can drive a transistor as well as a LED at

the same time, so controller functions including ``staging''

control can be performed. The LM3914 can also act as a

programmer, or sequencer.

The LM3914 is rated for operation from 0 § Cto a 70 § C. The

LM3914N is available in an 18-lead molded (N) package.

The following typical application illustrates adjusting of the

reference to a desired value, and proper grounding for accu-

rate operation, and avoiding oscillations.

Features

Y Drives LEDs, LCDs or vacuum fluorescents

Y Bar or dot display mode externally selectable by user

Y Expandable to displays of 100 steps

Y Internal voltage reference from 1.2V to 12V

Y Operates with single supply of less than 3V

Y Inputs operate down to ground

Y Output current programmable from 2 mA to 30 mA

Y No multiplex switching or interaction between outputs

Y Input withstands g 35V without damage or false outputs

Y LED driver outputs are current regulated, open-collec-

tors

Y Outputs can interface with TTL or CMOS logic

Y The internal 10-step divider is floating and can be refer-

enced to a wide range of voltages

Typical Applications

0V to 5V Bar Graph Meter

Note 1: Grounding method is typical of all uses.

The 2.2 m F tantalum or 10 m F aluminum electro-

lytic capacitor is needed if leads to the LED sup-

ply are 6 × or longer.

Ref Out V e 1.25

1 a

12.5

ILED j

TL/H/7970±1

C 1995 National Semiconductor Corporation

TL/H/7970

RRD-B30M115/Printed in U. S. A.

General Description

The LM3914 is a monolithic integrated circuit that senses

analog voltage levels and drives 10 LEDs, providing a linear

analog display. A single pin changes the display from a

moving dot to a bar graph. Current drive to the LEDs is

regulated and programmable, eliminating the need for resis-

tors. This feature is one that allows operation of the whole

system from less than 3V.

The circuit contains its own adjustable reference and accu-

rate 10-step voltage divider. The low-bias-current input buff-

er accepts signals down to ground, or V b , yet needs no

protection against inputs of 35V above or below ground.

The buffer drives 10 individual comparators referenced to

the precision divider. Indication non-linearity can thus be

held typically to

(/2

Absolute Maximum Ratings

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales

Office/Distributors for availability and specifications.

Power Dissipation (Note 5)

Molded DIP (N)

Storage Temperature Range

b 55 § Cto a 150 § C

Soldering Information

Dual-In-Line Package

Soldering (10 seconds)

260 § C

1365 mW

Plastic Chip Carrier Package

Vapor Phase (60 seconds) 215 § C

Infrared (15 seconds) 220 § C

See AN-450 ``Surface Mounting Methods and Their Effect

on Product Reliability'' for other methods of soldering sur-

face mount devices.

Supply Voltage

25V

Voltage on Output Drivers

25V

Input Signal Overvoltage (Note 3)

g 35V

Divider Voltage

b 100 mV to V a

Reference Load Current

10 mA

Electrical Characteristics (Notes 1 and 3)

Parameter

Conditions (Note 1)

Min Typ Max Units

COMPARATOR

Offset Voltage, Buffer and First

0V s V RLO e V RHI s 12V,

Comparator

I LED e 1mA

Offset Voltage, Buffer and Any Other

0V s V RLO e V RHI s 12V,

Comparator

I LED e 1mA

Gain ( D I LED / D V IN )

I L(REF) e 2 mA, I LED e 10 mA

mA/mV

Input Bias Current (at Pin 5)

0V s V IN s V a b 1.5V

100

Input Signal Overvoltage

No Change in Display

b 35

VOLTAGE-DIVIDER

Divider Resistance

Total, Pin 6 to 4

k X

Accuracy

(Note 2)

0.5

2 %

VOLTAGE REFERENCE

Output Voltage

0.1 mA s I L(REF) s 4 mA,

1.2

1.28

1.34

V a e V LED e 5V

Line Regulation

3V s V a s 18V

0.01

0.03 %/V

Load Regulation

0.1 mA s I L(REF) s 4 mA,

0.4

2 %

V a e V LED e 5V

Output Voltage Change with

0 § C s T A s a 70 § C, I L(REF) e 1 mA,

Temperature

V a e 5V

Adjust Pin Current

120

m A

OUTPUT DRIVERS

LED Current

V a e V LED e 5V, I L(REF) e 1 mA

LED Current Difference (Between

V LED e 5V

I LED e 2 mA

0.12

0.4

Largest and Smallest LED Currents)

I LED e 20 mA

1.2

LED Current Regulation

2V s V LED s 17V I LED e 2 mA

0.1

0.25

I LED e 20 mA

Dropout Voltage

I LED(ON) e 20 mA, V LED e 5V,

1.5

D I LED e 2mA

Saturation Voltage

I LED e 2.0 mA, I L(REF) e 0.4 mA

0.15

0.4

Output Leakage, Each Collector

(Bar Mode) (Note 4)

0.1

m A

Electrical Characteristics (Note 1) (Continued)

Parameter

Conditions (Note 1)

Min

Typ Max

Units

OUTPUT DRIVERS (Continued)

Output Leakage

(Dot Mode) (Note 4)

Pins 10±18

0.1

m A

Pin 1

150

450

m A

SUPPLY CURRENT

Standby Supply Current

V a e 5V, I L(REF) e 0.2 mA

2.4

4.2

(All Outputs Off)

V a e 20V, I L(REF) e 1.0 mA

6.1

9.2

Note 1: Unless otherwise stated, all specifications apply with the following conditions:

3V DC s V a s 20 V DC V REF ,V RHI ,V RLO s (V a b 1.5V)

3V DC s V LED s V a 0V s V IN s V a b 1.5V

b 0.015V s V RLO s 12 V DC T A ea 25 § C, I L(REF) e 0.2 mA, V LED e 3.0V, pin 9 connected to pin 3 (Bar Mode).

b 0.015V s V RHI s 12 V DC

For higher power dissipations, pulse testing is used.

Note 2: Accuracy is measured referred to a 10.000 V DC at pin 6, with 0.000 V DC at pin 4. At lower full-scale voltages, buffer and comparator offset voltage may add

significant error.

Note 3: Pin 5 input current must be limited to g 3 mA. The addition of a 39k resistor in series with pin 5 allows g 100V signals without damage.

Note 4: Bar mode results when pin 9 is within 20 mV of V a . Dot mode results when pin 9 is pulled at least 200 mV below V a or left open circuit. LED No. 10 (pin 10

output current) is disabled if pin 9 is pulled 0.9V or more below V LED .

Note 5: The maximum junction temperature of the LM3914 is 100 § C. Devices must be derated for operation at elevated temperatures. Junction to ambient thermal

resistance is 55 § C/W for the molded DIP (N package).

Definition of Terms

Accuracy: The difference between the observed threshold

voltage and the ideal threshold voltage for each compara-

tor. Specified and tested with 10V across the internal volt-

age divider so that resistor ratio matching error predomi-

nates over comparator offset voltage.

Adjust Pin Current: Current flowing out of the reference

adjust pin when the reference amplifier is in the linear re-

gion.

Comparator Gain: The ratio of the change in output current

(I LED ) to the change in input voltage (V IN ) required to pro-

duce it for a comparator in the linear region.

Dropout Voltage: The voltage measured at the current

source outputs required to make the output current fall by

10%.

Input Bias Current: Current flowing out of the signal input

when the input buffer is in the linear region.

LED Current Regulation: The change in output current

over the specified range of LED supply voltage (V LED )as

measured at the current source outputs. As the forward volt-

age of an LED does not change significantly with a small

change in forward current, this is equivalent to changing the

voltage at the LED anodes by the same amount.

Line Regulation: The average change in reference output

voltage over the specified range of supply voltage (V a ).

Load Regulation: The change in reference output voltage

(V REF ) over the specified range of load current (I L(REF) ).

Offset Voltage: The differential input voltage which must

be applied to each comparator to bias the output in the

linear region. Most significant error when the voltage across

the internal voltage divider is small. Specified and tested

with pin 6 voltage (V RHI ) equal to pin 4 voltage (V RLO ).

Typical Performance Characteristics

Supply Current vs

Operating Input Bias

Reference Voltage vs

Temperature

Current vs Temperature

Temperature

Reference Adjust Pin

LED Current-Regulation

LED Driver Saturation

Current vs Temperature

Dropout

Voltage

Input Current Beyond

LED Current vs

LED Driver Current

Signal Range (Pin 5)

Reference Loading

Regulation

Total Divider Resistance

vs Temperature

Common-Mode Limits

Output Characteristics

TL/H/7970±2

Block Diagram (Showing Simplest Application)

TL/H/7970±3

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