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 mov-
ing dot to a bar graph. Current drive to the LEDs is regulated
and programmable, eliminating the need for resistors. 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

%, 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 ex-
ternal 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 dis-
play 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 accu-
rate operation, and avoiding oscillations.

Features

Drives LEDs, LCDs or vacuum fluorescents

Bar or dot display mode externally selectable by user

Expandable to displays of 100 steps

Internal voltage reference from 1.2V to 12V

Operates with single supply of less than 3V

Inputs operate down to ground

Output current programmable from 2 mA to 30 mA

No multiplex switching or interaction between outputs

Input withstands

35V without damage or false outputs

LED driver outputs are current regulated,
open-collectors

Outputs can interface with TTL or CMOS logic

The internal 10-step divider is floating and can be
referenced to a wide range of voltages

January 2000

LM3914

Dot/Bar

Display

Driver

DS007970

www.national.com

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)

1365 mW

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

Storage Temperature Range

-55°C to +150°C

Soldering Information

Dual-In-Line Package

Soldering (10 seconds)

260°C

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.

Electrical Characteristics

(Notes 2, 4)

Parameter

Conditions (Note 2)

Min

Typ

Max

Units

COMPARATOR

Offset Voltage, Buffer and First
Comparator

RLO

= V

RHI

12V,

LED

= 1 mA

Offset Voltage, Buffer and Any Other
Comparator

RLO

= V

RHI

12V,

LED

= 1 mA

Gain (

LED

)

L(REF)

= 2 mA, I

LED

= 10 mA

mA/mV

Input Bias Current (at Pin 5)

- 1.5V

100

Input Signal Overvoltage

No Change in Display

-35

VOLTAGE-DIVIDER

Divider Resistance

Total, Pin 6 to 4

Accuracy

(Note 3)

0.5

VOLTAGE REFERENCE

Output Voltage

0.1 mA

L(REF)

4 mA,

= V

LED

= 5V

1.2

1.28

1.34

Line Regulation

18V

0.01

0.03

%/V

Load Regulation

0.1 mA

L(REF)

4 mA,

= V

LED

= 5V

0.4

Output Voltage Change with
Temperature

0°C

+70°C, I

L(REF)

= 1 mA,

= 5V

Adjust Pin Current

120

µA

OUTPUT DRIVERS

LED Current

= V

LED

= 5V, I

L(REF)

= 1 mA

LED Current Difference (Between
Largest and Smallest LED Currents)

LED

= 5V

LED

= 2 mA

0.12

0.4

LED

= 20 mA

1.2

LED Current Regulation

LED

17V

LED

= 2 mA

0.1

0.25

LED

= 20 mA

Dropout Voltage

LED(ON)

= 20 mA, V

LED

= 5V,

LED

= 2 mA

1.5

Saturation Voltage

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 1018

0.1

µA

Pin 1

150

450

µA

SUPPLY CURRENT

Standby Supply Current
(All Outputs Off)

= 5V,

L(REF)

= 0.2 mA

2.4

4.2

= 20V,

L(REF)

= 1.0 mA

6.1

9.2

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is func-
tional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guar-
antee 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.

LM3914

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Electrical Characteristics

(Notes 2, 4) (Continued)

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

3 V

20 V

REF

, V

RHI

, V

RLO

- 1.5V)

3 V

LED

- 1.5V

-0.015V

RLO

12 V

= +25°C, I

L(REF)

= 0.2 mA, V

LED

= 3.0V, pin 9 connected to pin 3 (Bar Mode).

-0.015V

RHI

12 V

For higher power dissipations, pulse testing is used.

Note 3: Accuracy is measured referred to +10.000 V

at pin 6, with 0.000 V

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

3 mA. 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 20 mV of V

. Dot mode results when pin 9 is pulled at least 200 mV 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).

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 di-
vider so that resistor ratio matching error predominates over
comparator offset voltage.

Adjust Pin Current: Current flowing out of the reference ad-
just 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

) 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

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 re-
gion. Most significant error when the voltage across the in-
ternal 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
Temperature

DS007970-2

Operating Input Bias
Current vs Temperature

DS007970-20

Reference Voltage vs
Temperature

DS007970-21

LM3914

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Functional Description

The simplifed LM3914 block diagram is to give the general
idea of the circuit's operation. A high input impedance buffer
operates with signals from ground to 12V, and is protected
against reverse and overvoltage signals. The signal is then
applied to a series of 10 comparators; each of which is bi-
ased to a different comparison level by the resistor string.

In the example illustrated, the resistor string is connected to
the internal 1.25V reference voltage. In this case, for each
125 mV that the input signal increases, a comparator will
switch on another indicating LED. This resistor divider can
be connected between any 2 voltages, providing that they
are 1.5V below V

and no less than V

. If an expanded scale

meter display is desired, the total divider voltage can be as
little as 200 mV. Expanded-scale meter displays are more
accurate and the segments light uniformly only if bar mode is
used. At 50 mV or more per step, dot mode is usable.

INTERNAL VOLTAGE REFERENCE

The reference is designed to be adjustable and develops a
nominal 1.25V between the REF OUT (pin 7) and REF ADJ
(pin 8) terminals. The reference voltage is impressed across
program resistor R1 and, since the voltage is constant, a
constant current I

then flows through the output set resistor

R2 giving an output voltage of:

Since the 120 µA current (max) from the adjust terminal rep-
resents an error term, the reference was designed to mini-
mize changes of this current with V

and load changes.

CURRENT PROGRAMMING

A feature not completely illustrated by the block diagram is
the LED brightness control. The current drawn out of the ref-
erence voltage pin (pin 7) determines LED current. Approxi-
mately 10 times this current will be drawn through each
lighted LED, and this current will be relatively constant de-
spite supply voltage and temperature changes. Current
drawn by the internal 10-resistor divider, as well as by the ex-
ternal current and voltage-setting divider should be included
in calculating LED drive current. The ability to modulate LED
brightness with time, or in proportion to input voltage and
other signals can lead to a number of novel displays or ways
of indicating input overvoltages, alarms, etc.

MODE PIN USE

Pin 9, the Mode Select input controls chaining of multiple
LM3914s, and controls bar or dot mode operation. The fol-
lowing tabulation shows the basic ways of using this input.
Other more complex uses will be illustrated in the applica-
tions.

Bar Graph Display: Wire Mode Select (pin 9)

directly to pin

3 (V

pin).

Dot Display, Single LM3914 Driver: Leave the Mode Select
pin open circuit.

Dot Display, 20 or More LEDs: Connect pin 9 of the

first

driver in the series (i.e., the one with the lowest input voltage
comparison points) to pin 1 of the next higher LM3914 driver.
Continue connecting pin 9 of lower input drivers to pin 1 of
higher input drivers for 30, 40, or more LED displays. The
last LM3914 driver in the chain will have pin 9 wired to pin 11.
All previous drivers should have a 20k resistor in parallel with
LED No. 9 (pin 11 to V

LED

Mode Pin Functional Description

This pin actually performs two functions. Refer to the simpli-
fied block diagram below.

DOT OR BAR MODE SELECTION

The voltage at pin 9 is sensed by comparator C1, nominally
referenced to (V

- 100 mV). The chip is in bar mode when

pin 9 is above this level; otherwise it's in dot mode. The com-
parator is designed so that pin 9 can be left open circuit for
dot mode.

Taking into account comparator gain and variation in the
100 mV reference level, pin 9 should be no more than 20 mV
below V

for bar mode and more than 200 mV below V

(or

open circuit) for dot mode. In most applications, pin 9 is ei-
ther open (dot mode) or tied to V

(bar mode). In bar mode,

pin 9 should be connected directly to pin 3. Large currents
drawn from the power supply (LED current, for example)
should not share this path so that large IR drops are avoided.

DOT MODE CARRY

In order for the display to make sense when multiple
LM3914s are cascaded in dot mode, special circuitry has
been included to shut off LED No. 10 of the first device when

DS007970-4

Block Diagram of Mode Pin Description

DS007970-5

High for bar

LM3914

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Mode Pin Functional Description

(Continued)

LED No. 1 of the second device comes on. The connection
for cascading in dot mode has already been described and is
depicted below.

As long as the input signal voltage is below the threshold of
the second LM3914, LED No. 11 is off. Pin 9 of LM3914
No. 1 thus sees effectively an open circuit so the chip is in
dot mode. As soon as the input voltage reaches the thresh-
old of LED No. 11, pin 9 of LM3914 No. 1 is pulled an LED
drop (1.5V or more) below V

LED

. This condition is sensed by

comparator C2, referenced 600 mV below V

LED

. This forces

the output of C2 low, which shuts off output transistor Q2, ex-
tinguishing LED No. 10.

LED

is sensed via the 20k resistor connected to pin 11. The

very small current (less than 100 µA) that is diverted from
LED No. 9 does not noticeably affect its intensity.

An auxiliary current source at pin 1 keeps at least 100 µA
flowing through LED No. 11 even if the input voltage rises
high enough to extinguish the LED. This ensures that pin 9 of
LM3914 No. 1 is held low enough to force LED No. 10 off
when

any higher LED is illuminated. While 100 µA does not

normally produce significant LED illumination, it may be no-
ticeable when using high-efficiency LEDs in a dark environ-
ment. If this is bothersome, the simple cure is to shunt LED
No. 11 with a 10k resistor. The 1V IR drop is more than the
900 mV worst case required to hold off LED No. 10 yet small
enough that LED No. 11 does not conduct significantly.

OTHER DEVICE CHARACTERISTICS

The LM3914 is relatively low-powered itself, and since any
number of LEDs can be powered from about 3V, it is a very
efficient display driver. Typical standby supply current (all

LEDs OFF) is 1.6 mA (2.5 mA max). However, any reference
loading adds 4 times that current drain to the V

(pin 3) sup-

ply input. For example, an LM3914 with a 1 mA reference pin
load (1.3k), would supply almost 10 mA to every LED while
drawing only 10 mA from its V

pin supply. At full-scale, the

IC is typically drawing less than 10% of the current supplied
to the display.

The display driver does not have built-in hysteresis so that
the display does not jump instantly from one LED to the next.
Under rapidly changing signal conditions, this cuts down
high frequency noise and often an annoying flicker. An "over-
lap" is built in so that at no time between segments are all
LEDs completely OFF in the dot mode. Generally 1 LED
fades in while the other fades out over a mV or more of
range (Note 3). The change may be much more rapid be-
tween LED No. 10 of one device and LED No. 1 of a

second

device "chained" to the first.

The LM3914 features individually current regulated LED
driver transistors. Further internal circuitry detects when any
driver transistor goes into saturation, and prevents other cir-
cuitry from drawing excess current. This results in the ability
of the LM3914 to drive and regulate LEDs powered from a
pulsating DC power source, i.e., largely unfiltered. (Due to
possible oscillations at low voltages a nominal bypass ca-
pacitor consisting of a 2.2 µF solid tantalum connected from
the pulsating LED supply to pin 2 of the LM3914 is recom-
mended.) This ability to operate with low or fluctuating volt-
ages also allows the display driver to interface with logic cir-
cuitry, opto-coupled solid-state relays, and low-current
incandescent lamps.

Cascading LM3914s in Dot Mode

DS007970-6

LM3914

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Typical Applications

(Continued)

Application Hints

Three of the most commonly needed precautions for using
the LM3914 are shown in the first typical application drawing
showing a 0V5V bar graph meter. The most difficult prob-
lem occurs when large LED currents are being drawn, espe-
cially in bar graph mode. These currents flowing out of the
ground pin cause voltage drops in external wiring, and thus
errors and oscillations. Bringing the return wires from signal
sources, reference ground and bottom of the resistor string
(as illustrated) to a single point very near pin 2 is the best so-
lution.

Long wires from V

LED

to LED anode common can cause os-

cillations. Depending on the severity of the problem 0.05 µF
to 2.2 µF decoupling capacitors from LED anode common to
pin 2 will damp the circuit. If LED anode line wiring is inac-
cessible, often similar decoupling from pin 1 to pin 2 will be
sufficient.

If LED turn ON seems slow (bar mode) or several LEDs light
(dot mode), oscillation or excessive noise is usually the prob-
lem. In cases where proper wiring and bypassing fail to stop
oscillations, V

voltage at pin 3 is usually below suggested

limits. Expanded scale meter applications may have one or
both ends of the internal voltage divider terminated at rela-

tively high value resistors. These high-impedance ends
should be bypassed to pin 2 with at least a 0.001 µF capaci-
tor, or up to 0.1 µF in noisy environments.

Power dissipation, especially in bar mode should be given
consideration. For example, with a 5V supply and all LEDs
programmed to 20 mA the driver will dissipate over 600 mW.
In this case a 7.5

resistor in series with the LED supply will

cut device heating in half. The negative end of the resistor
should be bypassed with a 2.2 µF solid tantalum capacitor to
pin 2 of the LM3914.

Turning OFF of most of the internal current sources is ac-
complished by pulling positive on the reference with a cur-
rent source or resistance supplying 100 µA or so. Alternately,
the input signal can be gated OFF with a transistor switch.

Other special features and applications characteristics will
be illustrated in the following applications schematics. Notes
have been added in many cases, attempting to cover any
special procedures or unusual characteristics of these appli-
cations. A special section called "Application Tips for the
LM3914 Adjustable Reference" has been included with
these schematics.

20-Segment Meter with Mode Switch

DS007970-14

The exact wiring arrangement of this schematic shows the need for Mode Select (pin 9) to sense the V

voltage exactly as it appears on pin 3.

Programs LEDs to 10 mA

LM3914

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Application Hints

(Continued)

APPLICATION TIPS FOR THE LM3914 ADJUSTABLE
REFERENCE

GREATLY EXPANDED SCALE (BAR MODE ONLY)

Placing the LM3914 internal resistor divider in parallel with a
section (

230

) of a stable, low resistance divider greatly

reduces voltage changes due to IC resistor value changes
with temperature. Voltage V

should be trimmed to 1.1V first

by use of R2. Then the voltage V

across the IC divider string

can be adjusted to 200 mV, using R5 without affecting V

LED current will be approximately 10 mA.

NON-INTERACTING ADJUSTMENTS FOR EXPANDED
SCALE METER (4.5V to 5V, Bar

or Dot Mode)

This arrangement allows independent adjustment of LED
brightness regardless of meter span and zero adjustments.

First, V

is adjusted to 5V, using R2. Then the span (voltage

across R4) can be adjusted to exactly 0.5V using R6 without
affecting the previous adjustment.

R9 programs LED currents within a range of 2.2 mA to 20 mA
after the above settings are made.

ADJUSTING LINEARITY OF SEVERAL STACKED
DIVIDERS

Three internal voltage dividers are shown connected in se-
ries to provide a 30-step display. If the resulting analog meter
is to be accurate and linear the voltage on each divider must
be adjusted, preferably without affecting any other adjust-
ments. To do this, adjust R2 first, so that the voltage across
R5 is exactly 1V. Then the voltages across R3 and R4 can
be independently adjusted by shunting each with selected
resistors of 6 k

or higher resistance. This is possible be-

cause the reference of LM3914 No. 3 is acting as a constant
current source.

The references associated with LM3914s No. 1 and No. 2
should have their Ref Adj pins (pin 8) wired to ground, and
their Ref Outputs loaded by a 620

resistor to ground. This

makes available similar 20 mA current outputs to all the
LEDs in the system.

If an independent LED brightness control is desired (as in
the previous application), a unity gain buffer, such as the
LM310, should be placed between pin 7 and R1, similar to
the previous application.

Greatly Expanded Scale (Bar Mode Only)

DS007970-15

LM3914

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Application Hints

(Continued)

Other Applications

"Slow" -- fade bar or dot display (doubles resolution)

20-step meter with single pot brightness control

10-step (or multiples) programmer

Multi-step or "staging" controller

Combined controller and process deviation meter

Direction and rate indicator (to add to DVMs)

Exclamation point display for power saving

Graduations can be added to dot displays. Dimly light ev-
ery other LED using a resistor to ground

Electronic "meter-relay" -- display could be circle or
semi-circle

Moving "hole" display -- indicator LED is dark, rest of bar
lit

Drives vacuum-fluorescent and LCDs using added pas-
sive parts

Non-Interacting Adjustments for Expanded Scale Meter (4.5V to 5V, Bar

or Dot Mode)

DS007970-16

Adjusting Linearity of Several Stacked Dividers

DS007970-17

LM3914

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Physical Dimensions

inches (millimeters) unless otherwise noted (Continued)

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2. A critical component is any component of a life

support device or system whose failure to perform
can be reasonably expected to cause the failure of
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Dual-In-Line Package (N)

Order Number LM3914N

NS Package Number N18A

Discontinued, Life Time Buy date 12/20/99

LM3914

Dot/Bar

Display

Driver

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

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