LM3914.pdf

February 2003

LM3914

Dot/Bar Display Driver

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

buffer accepts signals down to ground, or V − , 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 1 ⁄ 2 %, 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 circuit.

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 control. 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 effects

can be achieved by modulating these currents. The indi-

vidual 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 program-

mer, or sequencer.

The LM3914 is rated for operation from 0˚C to +70˚C. The

LM3914N-1 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 ac-

curate operation, and avoiding oscillations.

Features

n Drives LEDs, LCDs or vacuum fluorescents

n Bar or dot display mode externally selectable by user

n Expandable to displays of 100 steps

n Internal voltage reference from 1.2V to 12V

n Operates with single supply of less than 3V

n Inputs operate down to ground

n Output current programmable from 2 mA to 30 mA

n No multiplex switching or interaction between outputs

n Input withstands ± 35V without damage or false outputs

n LED driver outputs are current regulated,

open-collectors

n Outputs can interface with TTL or CMOS logic

n The internal 10-step divider is floating and can be

referenced to a wide range of voltages

DS007970

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Typical Applications

0V to 5V Bar Graph Meter

00797001

Note: Grounding method is typical of all uses. The 2.2µF tantalum or 10 µF aluminum electrolytic capacitor is needed if leads to the LED supply are 6" or

longer.

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Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Power Dissipation (Note 6)

Molded DIP (N)

Storage Temperature Range

−55˚C to +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

surface mount devices.

Supply Voltage

25V

Voltage on Output Drivers

25V

Input Signal Overvoltage (Note 4)

± 35V

Divider Voltage

−100 mV to V +

Reference Load Current

10 mA

Electrical Characteristics (Notes 2, 4)

Parameter

Conditions (Note 2)

Min Typ Max Units

COMPARATOR

Offset Voltage, Buffer and First

Comparator

≤

V RLO =V RHI ≤

12V,

I LED =1mA

Offset Voltage, Buffer and Any Other

Comparator

0V ≤ V RLO =V RHI ≤ 12V,

I LED =1mA

Gain ( ∆ I LED / ∆ V IN )

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

mA/mV

Input Bias Current (at Pin 5)

≤

V IN

≤

V + − 1.5V

100

Input Signal Overvoltage

No Change in Display

−35

VOLTAGE-DIVIDER

Divider Resistance

Total, Pin 6 to 4

Ω

Accuracy

(Note 3)

0.5

VOLTAGE REFERENCE

Output Voltage

0.1 mA

≤

I L(REF)

≤

4 mA,

1.2

1.28

1.34

V + =V LED =5V

Line Regulation

≤

V +

≤

18V

0.01

0.03

%/V

Load Regulation

0.1 mA

≤

I L(REF) ≤

4 mA,

0.4

V + =V LED =5V

Output Voltage Change with

Temperature

0˚C

≤

T A ≤

+70˚C, I L(REF) = 1 mA,

V + =5V

Adjust Pin Current

120

µA

OUTPUT DRIVERS

LED Current

V + =V LED = 5V, I L(REF) = 1 mA

LED Current Difference (Between

Largest and Smallest LED Currents)

V LED =5V

I LED = 2 mA

0.12

0.4

I LED =20mA

1.2

LED Current Regulation

≤

V LED ≤

17V

I LED = 2 mA

0.1

0.25

I LED =20mA

Dropout Voltage

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

∆ I LED =2mA

1.5

Saturation Voltage

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

0.15

0.4

Output Leakage, Each Collector

(Bar Mode) (Note 5)

0.1

µA

Output Leakage

(Dot Mode) (Note 5) Pins 10–18

0.1

µA

Pin 1

150

450

µA

SUPPLY CURRENT

Standby Supply Current

(All Outputs Off)

V + = 5V,

I L(REF) = 0.2 mA

2.4

4.2

V + = 20V,

I L(REF) = 1.0 mA

6.1

9.2

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Electrical Characteristics (Notes 2, 4) (Continued)

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is

functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which

guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit

is given, however, the typical value is a good indication of device performance.

Note 2: Unless otherwise stated, all specifications apply with the following conditions:

3V DC

≤

V +

≤

20 V DC

V REF ,V RHI ,V RLO

≤

(V + − 1.5V)

3V DC

≤

V LED

≤

V +

≤

V IN

≤

V + − 1.5V

−0.015V

≤

V RLO ≤

12V DC

T A = +25˚C, I L(REF) = 0.2 mA, V LED = 3.0V, pin 9 connected to pin 3 (Bar Mode).

12 V DC

For higher power dissipations, pulse testing is used.

Note 3: Accuracy is measured referred to +10.000V 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 4: Pin 5 input current must be limited to ± 3mA. The addition of a 39k resistor in series with pin 5 allows ± 100V signals without damage.

Note 5: Bar mode results when pin 9 is within 20mV of V + . Dot mode results when pin 9 is pulled at least 200mV below V + 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 6: 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).

≤

V RHI ≤

Definition of Terms

Accuracy: The difference between the observed threshold

voltage and the ideal threshold voltage for each comparator.

Specified and tested with 10V across the internal voltage

divider so that resistor ratio matching error predominates

over comparator offset voltage.

Adjust Pin Current: Current flowing out of the reference

adjust pin when the reference amplifier is in the linear region.

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

voltage 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 + ).

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 ).

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−0.015V

Typical Performance Characteristics

Supply Current vs

Temperature

Operating Input Bias

Current vs Temperature

00797002

00797020

Reference Voltage vs

Temperature

Reference Adjust Pin

Current vs Temperature

00797021

00797022

LED Current-Regulation

Dropout

LED Driver Saturation

Voltage

00797023

00797024

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