Datasheet LM3916 Datasheet (National Semiconductor)

LM3916
Dot/Bar Display Driver

General Description

The LM3916 is a monolithic integrated circuit that senses
analog voltage levels and drives ten LEDs, LCDs or vacuum
fluorescent displays, providing an electronic version of the
popular VU meter. One pin changes the display from a bar
graph to a moving dot display. LED current drive is regulated
and programmable, eliminating the need for current limiting
resistors. The whole display system can operate from a
single supply as low as 3V or as high as 25V.

The IC contains an adjustable voltage reference and an
accurate ten-step voltage divider. The high-impedance input
buffer accepts signals down to ground and up to within 1.5V
of the positive supply. Further, it needs no protection against
inputs of
parators referenced to the precision divider. Accuracy is
typically better than 0.2 dB.

Audio applications include average or peak level indicators,
and power meters. Replacing conventional meters with an
LED bar graph results in a faster responding, more rugged
display with high visibility that retains the ease of interpreta­tion of an analog display.

The LM3916 is extremely easy to apply. A 1.2V full-scale
meter requires only one resistor in addition to the ten LEDs.
One more resistor programs the full-scale anywhere from

1.2V to 12V independent of supply voltage. LED brightness
is easily controlled with a single pot.

±

35V. The input buffer drives 10 individual com-

January 2000

The LM3916 is very versatile. The outputs can drive LCDs,
vacuum fluorescents and incandescent bulbs as well as
LEDs of any color. Multiple devices can be cascaded for a
dot or bar mode display for increased range and/or resolu­tion. Useful in other applications are the linear LM3914 and
the logarithmic LM3915.

Features

n Fast responding electronic VU meter
n Drivers LEDs, LCDs, or vacuum fluorescents
n Bar or dot display mode externally selectable by user
n Expandable to displays of 70 dB
n Internal voltage reference from 1.2V to 12V
n Operates with single supply of 3V to 25V
n Inputs operate down to ground
n Output current programmable from 1 mA to 30 mA
n Input withstands
n Outputs are current regulated, open collectors
n Directly drives TTL or CMOS
n The internal 10-step divider is floating and can be

referenced to a wide range of voltages

The LM3916 is rated for operation from 0˚C to +70˚C. The
LM3916N-1 is available in an 18-lead molded DIP package.

±

35V without damage or false outputs

LM3916 Dot/Bar Display Driver

© 2004 National Semiconductor Corporation DS007971 www.national.com

Typical Applications

LM3916

0V to 10V VU Meter

00797101

Notes: Capacitor C1 is required if leads to the LED supply are 6" or longer.

Circuit as shown is wired for dot mode. For bar mode, connect pin 9 to pin 3. V
dissipation.

must be kept below 7V or dropping resistor should be used to limit IC power

LED

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LM3916

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

Input Signal Overvoltage (Note 4)

Divider Voltage −100 mV to V

Reference Load Current 10 mA

Storage Temperature Range −55˚C to +150˚C

Lead Temperature

(Soldering, 10 seconds) 260˚C

±

35V

Supply Voltage 25V

Voltage on Output Drivers 25V

Electrical Characteristics (Notes 2, 4)

Parameter Conditions (Note 2) Min Typ Max Units

COMPARATORS

Offset Voltage, Buffer and First Comparator 0V ≤ V

Offset Voltage, Buffer and Any Other Comparator 0V ≤ V

Gain (∆I

/ ∆VIN)I

LED

Input Bias Current (at Pin 5) 0V ≤ V

I

LED

I

LED

(REF)

RLO=VRHI

=1mA

RLO=VRHI

=1mA

= 2 mA, I

≤ (V+−1.5V) 25 100 nA

IN

Input Signal Overvoltage No Change in Display −35 35 V

VOLTAGE DIVIDER

Divider Resistance Total, Pin 6 to 4 8 12 17 kΩ

Relative Accuracy (Input Change
Between Any Two Threshold Points)

(Note 3)

−1 dB ≤ V

−7 dB ≤ V

IN

IN

−10 dB ≤ V

Absolute Accuracy (Note 3)

=2,1,0,−1dB

V

IN

= −3, −5 dB

V

IN

= −7, −10, −20 dB

V

IN

VOLTAGE REFERENCE

Output Voltage 0.1 mA ≤ I

+

V

Line Regulation 3V ≤ V

Load Regulation 0.1 mA ≤ I

+

V

Output Voltage Change with Temperature 0˚C ≤ T

+

V

L(REF)

=V

LED
+

≤ 18V 0.01 0.03 %/V

L(REF)

=V

LED

≤ +70˚C, I

A

=V

LED

Adjust Pin Current 75 120 µA

OUTPUT DRIVERS

LED Current V

LED Current Difference (Between Largest and
Smallest LED Currents)

LED Current Regulation 2V ≤ V

Dropout Voltage I

Saturation Voltage I

+

V

LED

V

LED

I

LED

I

LED

LED(ON)

∆I

LED

LED

=V

LED

= 5V, I
= 5V, I

LED

2mA
=20mA

=20mA@V

=2mA

= 2.0 mA, I

Output Leakage, Each Collector Bar Mode (Note 5) 0.1 100 µA

Output Leakage Dot Mode (Note 5)

Pins 10– 18 0.1 100 µA

Pin 1 60 150 450 µA

SUPPLY CURRENT

LED

≤ 3dB
≤ −1 dB

≤ −7 dB

IN

= 5Vg

=5V

=5V

= 5V, I

LED

LED

≤ 17V

≤ 12V,

≤ 12V,

310 mV

315 mV

= 10 mA 3 8 mA/mV

0.75

1.5

2.5

−0.25

−0.5

−1

≤ 4 mA,

1.2 1.28 1.34 V

≤ 4 mA,

= 1 mA,

L(REF)

= 1 mA 7 10 13 mA

L(REF)

=2mA
=20mA

1.0

1.25

2.0

3.0

2.5

2.5

+0.25

+0.5

+1

0.4 2 %

1%

0.12

1.2

0.4
3

0.110.25
3

= 5V,

LED

= 0.4 mA 0.15 0.4 V

L(REF)

1.5 V

dB
dB
dB

dB
dB
dB

mA
mA

mA
mA

+

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Electrical Characteristics (Notes 2, 4) (Continued)

LM3916

Parameter Conditions (Note 2) Min Typ Max Units

Standby Supply Current
(All Outputs Off)

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

≤ V+≤ 20 V

DC

≤ V

3V

DC

−0.015V ≤ V

Note 3: Accuracy is measured referred to +3 dB = +10.000 V
comparator offset voltage may add significant error. See table for threshold voltages.

Note 4: Pin 5 input current must be limited to

Note 5: Bar mode results when pin 9 is within 20 mV of V

disabled if pin 9 is pulled 0.9V or more below V

Note 6: The maximum junction temperature of the LM3916 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).

LED

RHI

≤ V

≤ 12 V

DC

+

−0.015V ≤ V

V

REF,VRHI,VRLO

0V ≤ VIN≤ V+− 1.5V

DC

≤ 12 V

RLO

DC

≤ (V+− 1.5V) For higher power dissipations, pulse testing is used.

±

3 mA. The addition of a 39k resistor in series with pin 5 allows±100V signals without damage.

.

LED

+

V

= + 5V, I

+

= + 20V, I

V

TA= 25˚C, I

at pin 5, with +10.000 VDCat pin 6, and 0.000 VDCat pin 4. At lower full-scale voltages, buffer and

DC

+

. Dot mode results when pin 9 is pulled at least 200 mV below V+. LED #10 (pin 10 output current) is

L(REF)

= 0.2 mA

L(REF)

= 1.0 mA

L(REF)

= 0.2 mA, pin 9 connected to pin 3 (bar mode).

2.4

6.1

4.2

9.2

LM3916 Threshold Voltage (Note 3)

dB

Min Typ Max Min Typ Max

3 9.985 10.000 10.015 −3

1

±

2

⁄48.660 8.913 9.173 −5

1

±

1

⁄47.718 7.943 8.175 −7±1 2.818 3.162 3.548

1

±

0

⁄46.879 7.079 7.286 −10±1 1.995 2.239 2.512

1

±

−1

⁄25.957 6.310 6.683 −20±1 0.631 0.708 0.794

Volts

dB

1

±

⁄24.732 5.012 5.309

1

±

⁄23.548 3.981 4.467

Volts

mA
mA

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Typical Performance Characteristics

LM3916

Supply Current vs

Temperature

Reference Voltage vs

Temperature

00797135

Operating Input Bias

Current vs Temperature

00797136

Reference Adjust Pin

Current vs Temperature

LED Current-Regulation

Dropout

00797137

00797139

00797138

LED Driver Saturation

Voltage

00797140

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Typical Performance Characteristics (Continued)

LM3916

Input Current Beyond

Signal Range (Pin 5)

LED Driver Current

Regulation

LED Current vs

Referenced Loading

00797141

00797142

Total Divider Resistance

vs Temperature

00797143

Common-Mode Limits Output Characteristics

00797145

00797144

00797146

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Block Diagram (Showing Simplest Application)

LM3916

00797104

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Functional Description

The simplified LM3916 block diagram is included to give the

LM3916

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 biased 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. As the input voltage
varies from 0 to 1.25, the comparator outputs are driven low
one by one, switching on the LED indicators. The resistor
divider can be connected between any 2 voltages, providing
that they are at least 1.5V below V

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

1

R2 giving an output voltage of:

+

and no lower than V−.

lighted LED, and this current will be relatively constant de­spite supply voltage and temperature changes. Current
drawn by the internal 10-resistor divider, as well as by the
external 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.

The LM3916 outputs are current-limited NPN transistors as
shown below. An internal feedback loop regulates the tran­sistor drive. Output current is held at about 10 times the
reference load current, independent of output voltage and
processing variables, as long as the transistor is not satu­rated.

LM3916 Output Circuit

00797106

00797105

Since the 120 µA current (max) from the adjust terminal
represents an error term, the reference was designed to
minimize changes of this current with V

+

and load changes.
For correct operation, reference load current should be be­tween 80 µA and 5 mA. Load capacitance should be less
than 0.05 µF.

CURRENT PROGRAMMING

A feature not completely illustrated by the block diagram is
the LED brightness control. The current drawn out of the
reference voltage pin (pin 7) determines LED current. Ap­proximately 10 times this current will be drawn through each

Outputs may be run in saturation with no adverse effects,
making it possible to directly drive logic. The effective satu­ration resistance of the output transistors, equal to R

plus

E

the transistors’ collector resistance, is about 50Ω. It’s also
possible to drive LEDs from rectified AC with no filtering. To
avoid oscillations, the LED supply should be bypassed with a

2.2 µF tantalum or 10 µF aluminum electrolytic capacitor.

MODE PIN USE

Pin 9, the Mode Select input, permits chaining of multiple
devices, and controls bar or dot mode operation. The follow­ing tabulation shows the basic ways of using this input. Other
more complex uses will be illustrated in the applications.

Bar Graph Display: Wire Mode Select (pin 9) directly to pin

+

pin).

3(V
Dot Display, Single LM3916 Driver: Leave the Mode Select

pin open circuit.
Dot Display, 20 or More LEDs: Connect pin 9 of the first

drivers in the series (i.e., the one with the lowest input
voltage comparison points) to pin 1 of the next higher
LM3916 driver. Continue connecting pin 9 of lower input
drivers to pin 1 of higher input drivers for 30 or more LED
displays. The last LM3916 driver in the chain will have pin 9
left open. All previous drivers should have a 20k resistor in
parallel with LED #9 (pin 11 to V

LED

).

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Mode Pin Functional Description

This pin actually performs two functions. Refer to the simpli­fied block diagram below.

Block Diagram of Mode Pin Function

*High for bar

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
comparator 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
open circuit) for dot mode. In most applications, pin 9 is
either open (dot mode) or tied to V

+

for bar mode and more than 200 mV below V+(or

+

(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.

00797107

DOT MODE CARRY

In order for display to make sense when multiple drivers are
cascaded in dot mode, special circuitry has been included to
shut off LED #10 of the first device when LED #1 of the
second device comes on. The connection for cascading in
dot mode has already been described and is depicted in
Figure 1.

As long as the input signal voltage is below the threshold of
the second driver, LED #11 is off. Pin 9 of driver #1 thus sees
effectively an open circuit so the chip is in dot mode. As soon
as the input voltage reaches the threshold of LED #11, pin 9
of driver #1 is pulled an LED drop (1.5V or more) below

. This condition is sensed by comparator C2, refer-

V

LED

enced 600 mV below V

. This forces the output of C2 low,

LED

which shuts off output transistor Q2, extinguishing LED #10.

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

V

LED

very small current (less than 100 µA) that is diverted from
LED #9 does not noticeably affect its intensity.

An auxiliary current source at pin 1 keeps at least 100 µA
flowing through LED #11 even if the input voltage rises high
enough to extinguish the LED. This ensures that pin 9 of
driver #1 is held low enough to force LED #10 off when any
higher LED is illuminated. While 100 µA does not normally
produce significant LED illumination, it may be noticeable
when using high-efficiency LEDs in a dark environment. If
this is bothersome, the simple cure is to shunt LED #11 (and
LED #1) with a 10k resistor. The 1V 1R drop is more than the
900 mV worst case required to hold off LED #10 yet small
enough that LED #11 does not conduct significantly.

In some circuits a number of outputs on the higher device
are not used. Examples include the high resolution VU meter
and the expanded range VU meter circuits (see Typical
Applications). To provide the proper carry sense voltage in
dot mode, the LEDs of the higher driver IC are tied to V

LED

through two series-connected diodes as shown in Figure 2.
Shunting the diodes with a 1k resistor provides a path for
driver leakage current.

LM3916

FIGURE 1. Cascading LM3914/15/16 Series in Dot Mode

00797108

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Mode Pin Functional Description (Continued)

LM3916

FIGURE 2. Cascading Drivers in Dot Mode with Pin 1 of Driver #2 Unused

00797109

OTHER DEVICE CHARACTERISTICS

The LM3915 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. However, any reference loading adds
4 times that current drain to the V

+

(pin 3) supply input. For
example, an LM3915 witha1mAreference 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 “over­lap” is built in so that at no time are all segments completely
off the dot mode. Generally one LED fades in while the other
fades out over a 1 mV range. The change may be much
more rapid between LED #10 of one device and LED #1 of a
second device cascaded.

Application Hints

The most difficult problem occurs when large LED currents
are being drawn, especially 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 to a single point very near pin 2 is
the best solution.

Long wires from V
oscillations. The usual cure is bypassing the LED anodes
with a 2.2 µF tantalum or 10 µF aluminum electrolytic ca­pacitor. If the LED anode line wiring is inaccessible, often a

0.1 µF capacitor from pin 1 to pin 2 will be sufficient.
If there is a large amount of LED overlap in the bar mode,

oscillation or excessive noise is usually the problem. In
cases where proper wiring and bypassing fail to stop oscil­lations, V

+

voltage at pin 3 is usually below suggested limits.
When several LEDs are lit in dot mode, the problem is
usually an AC component of the input signal which should be
filtered out. Expanded scale meter applications may have
one or both ends of the internal voltage divider terminated at
relatively high value resistors. These high-impedance ends
should be bypassed to pin 2 with 0.1 µF.

to LED anode common can cause

LED

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 7.5Ω 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 or 10 µF
aluminum electrolytic capacitor to pin 2.

TIPS ON RECTIFIER CIRCUITS

The simplest way to display an AC signal using the LM3916
is to apply it right to pin 5 unrectified. Since the LED illumi­nated represents the instantaneous value of the AC wave­form, one can readily discern both peak and average values
of audio signals in this manner. The LM3916 will respond to
positive half-cycles only but will not be damaged by signals

±

35V (or up to±100V if a 39k resistor is in series with

up to
the input). A smear or bar type display results even though
the LM3916 is connected for dot mode. The LEDs should be
run at 20 mA to 30 mA for high enough average intensity.

True average or peak detection requires rectification. If an
LM3916 is set up with 10V full scale across its voltage
divider, the turn-on point for the first LED is only 450 mV. A
simple silicon diode rectifier won’t work well at the low end
due to the 600 mV diode threshold. The half-wave peak
detector in Figure 3 uses a PNP emitter-follower in front of
the diode. Now, the transistor’s base-emitter voltage cancels
out the diode offset, within about 100 mV. This approach is
usually satisfactory when a single LM3916 is used for a 23
dB display.

Display circuits such as the extended range VU meter using
two or more drivers for a dynamic range of 40 dB or greater
require more accurate detection. In the precision half-wave
rectifier of Figure 4 the effective diode offset is reduced by a
factor equal to the open-loop gain of the op amp. Filter
capacitor C2 charges through R3 and discharges through
R2 and R3, so that appropriate selection of these values
results in either a peak or an average detector. The circuit
has a gain equal to R2/R1.

It’s best to capacitively couple the input. Audio sources
frequently have a small DC offset that can cause significant
error at the low end of the log display. Op amps that slew
quickly, such as the LF351, LF353 or LF356, are needed to
faithfully respond to sudden transients. It may be necessary
to trim out the op amp DC offset voltage to accurately cover
a 60 dB range. Best results are obtained if the circuit is

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Application Hints (Continued)

adjusted for the correct output when a low-level AC signal
(10 to 20 mV) is applied, rather than adjusting for zero output
with zero input.

LM3916

*DC Couple

00797110

FIGURE 3. Half-Wave Peak Detector

D1, D2: 1N914 or 1N4148

00797111

Average Peak

R2 1k 100k

R3 100k 1k

R1 = R2 for AV=1
R1 = R2/10 for A
C1 = 10/R1

V

=10

FIGURE 4. Precision Half-Wave Rectifier

For precision full-wave averaging use the circuit in Figure 5.
Using 1% resistors for R1 through R4, gain for positive and
negative signal differs by only 0.5 dB worst case. Substitut­ing 5% resistors increases this to 2 dB worst case. (A 2 dB

±

gain difference means that the display may have a

1dB
error when the input is a nonsymmetrical transient). The
averaging time constant is R5

C2. A simple modification

•

results in the precision full-wave detector of Figure 6. Since
the filter capacitor is not buffered, this circuit can drive only
high impedance loads such as the input of an LM3916.

D1, D2: 1N914 or 1N4148

00797112

FIGURE 5. Precision Full-Wave Average Detector

00797113

D1, D2, D3, D4: 1N914 OR 1N4148

Attack and decay time to DIN PPM spec. Response down 1 dB for 10 ms
tone burst. Decays 20 dB in 1.5s.

FIGURE 6. Precision Full-Wave Peak Detector

AUDIO METER STANDARDS

VU Meter

The audio level meter most frequently encountered is the VU
meter. Its characteristics are defined as the ANSI specifica­tion C165. The LM3916’s outputs correspond to the meter
indications specified with the omission of the −2 VU indica­tion. The VU scale divisions differ slightly from a linear scale
in order to obtain whole numbers in dB.

Some of the most important specifications for an AC meter
are its dynamic characteristics. These define how the meter
responds to transients and how fast the reading decays. The
VU meter is a relatively slow full-wave averaging type, speci­fied to reach 99% deflection in 300 ms and overshoot by 1 to

1.5%. In engineering terms this means a slightly under-

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Application Hints (Continued)

damped second order response with a resonant frequency

LM3916

of2.1HzandaQof0.62. Figure 7 depicts a simple rectifier/
filter circuit that meets these criteria.

Design Equations

GAIN R5 R6 C2 C3

1 100k 43k 2.0 0.56 µF

10 1M 100k 1.0 0.056 µF

FIGURE 7. Full-Wave Average Detector to VU Meter Specifications*

Peak Program Meter

The VU meter, originally intended for signals sent via tele­phone lines, has shortcomings when used in high fidelity
systems. Due to its slow response time, a VU meter will not
accurately display transients that can saturate a magnetic
tape or drive an amplifier into clipping. The fast-attack peak
program meter (PPM) which does not have this problem is
becoming increasingly popular.

While several European organizations have specifications
for peak program meters, the German DIN specification
45406 is becoming a de facto standard. Rather than respond
instantaneously to peak, however, PPM specifications re­quire a finite “integration time” so that only peaks wide
enough to be audible are displayed. DIN 45406 calls for a
response of 1 dB down from steady-state for a 10 ms tone
burst and 4 dB down fora3mstone burst. These require­ments are consistent with the other frequently encountered
spec of 2 dB down fora5msburst and are met by an attack
time constant of 1.7 ms.

00797114

The specified return time of 1.5s to −20 dB requires a
650 ms decay time constant. The full-wave peak detector of
Figure 6 satisfies both the attack and decay time criteria.

Cascading The LM3916

The LM3916 by itself covers the 23 dB range of the conven­tional VU meter. To display signals of 40 dB or 70 dB
dynamic range, the LM3916 may be cascaded with the 3
dB/step LM3915s. Alternatively, two LM3916s may be cas­caded for increased resolution over a 28 dB range. Refer to
the Extended Range VU Meter and High Resolution VU
Meter in the Typical Applications section for the complete
circuits for both dot and bar mode displays.

To obtain a display that makes sense when an LM3915 and
an LM3916 are cascaded, the −20 dB output from the
LM3916 is dropped. The full-scale display for the LM3915 is
set at 3 dB below the LM3916’s −10 dB output and the rest
of the thresholds continue the 3 dB/step spacing. A simple,
low cost approach is to set the reference voltage of the two
chips 16 dB apart as in Figure 5. The LM3915, with pin 8
grounded, runs at 1.25V full-scale. R1 and R2 set the

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Application Hints (Continued)

LM3916’s reference 16 dB higher or 7.89V. Variation in the
two on-chip references and resistor tolerance may cause a

±

1 dB error in the −10 dB to −13 dB transition. If this is

objectionable, R2 can be trimmed.
The drawback of the aforementioned approach is that the

threshold of LED #1 on the LM3915 is only 56 mV. Since

LM3916

comparator offset voltage may be as high as 10 mV, large
errors can occur at the first few thresholds. A better ap­proach, as shown in Figure 9, is to keep the reference the
same for both drivers (10V in the example) and amplify the
input signal by 16 dB ahead of the LM3915. Alternatively,
instead of amplifying, input signals of sufficient amplitude
can be fed directly to the LM3916 and attenuated by 16 dB to
drive the LM3915.

V

REF2

. 7.89V

00797115

FIGURE 8. Low Cost Circuit for 40 dB Display

FIGURE 9. Improved Circuit for 40 dB Display

00797116

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Application Hints (Continued)

To extend this approach to get a 70 dB display, another

LM3916

30 dB of amplification must be placed in the signal path
ahead of the lowest LM3915. Extreme care is required as the
lowest LM3915 displays input signals down to 2 mV! Several
offset nulls may be required. High currents should not share
the same path as the low level signal. Also power line wiring
should be kept away from signal lines.

TIPS ON REFERENCE VOLTAGE AND LED CURRENT PROGRAMMING

Single Driver

The equations in Figure 10 illustrate how to choose resistor
values to set reference voltage for the simple case where no
LED intensity adjustment is required. A LED current of
10 mA to 20 mA generally produces adequate illumination.
Having 10V full-scale across the internal voltage divider
gives best accuracy by keeping signal level high relative to
the offset voltage of the internal comparators. However, this
causes 1 mA to flow from pin 7 into the divider which means
that the LED current will be at least 10 mA. R1 will typically
be between 1 kΩ and5kΩ. To trim the reference voltage,
vary R2.

The current in Figure 11 shows how to add a LED intensity
control which can vary LED current from 5 mA to 28 mA.
Choosing V
increasing the intensity adjustment range. The reference
adjustment has some effect on LED intensity but the reverse
is not true.

= 5V lowers the current drawn by the ladder,

REF

00797117

5mA≤ I

≤ 28 mA@V

LED

REF

=5V

00797118

FIGURE 11. Varying LED Intensity

Multiple Drivers

Figure 12 shows how to obtain a common reference trim and
intensity control for two drivers. The two ICs may be con­nected in cascade or may be handling separate channels for
stereo. This technique can be extended for larger numbers
of drivers by varying the values of R1, R2 and R3. Because
the LM3915 has a greater ladder resistance, R5 was picked
less than R7 in such a way as to provide equal reference
load currents. The ICs’ internal references track within
100 mV so that worst case error from chip to chip is only 0.2
dB for V

REF

=5V.

The scheme in Figure 13 is useful when the reference and
LED intensity must be adjusted independently over a wide
range. The R

voltage can be adjusted from 1.2V to 10V

HI

with no effect on LED current. Since the internal divider here
does not load down the reference, minimum LED current is
much lower. At the minimum recommended reference load
of 80 µA, LED current is about 0.8 mA. The resistor values
shown give a LED current range from 1.5 mA to 25 mA.

At the low end of the intensity adjustment, the voltage drop
across the 510Ω current-sharing resistors is so small that
chip to chip variation in reference voltage may yield a visible
variation in LED intensity. The optional approach shown of
connecting the bottom end of the intensity control pot to a
negative supply overcomes this problem by allowing a larger
voltage drop across the (larger) current-sharing resistors.

FIGURE 10. Design Equations for Fixed LED Intensity

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Application Hints (Continued)

LM3916

5mA≤ I

=5V

V

REF

LED

≤ 28 mA

00797119

FIGURE 12. Independent Adjustment of Reference Voltage and LED Intensity for Multiple Drivers

1.25V ≤ V

1.5 mA ≤ I

Optional circuit for improved intensity matching at low currents. See text.

REF

LED

≤ 10V

≤ 25 mA

FIGURE 13. Wide-Range Adjustment of Reference Voltage and LED intensity for Multiple Drivers

Other Applications

For increased resolution, it’s possible to obtain a display with
a smooth transition between LEDs. This is accomplished by
superimposing an AC waveform on top of the input level as

00797120

shown in Figure 14. The signal can be a triangle, sawtooth or
sine wave from 60 Hz to 1 kHz. The display can be run in
either dot or bar mode.

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Other Applications (Continued)

LM3916

00797121

FIGURE 14. 0V to 10V VU Meter with Smooth Transitions

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00797122

LM3916

Extended Range VU Meter (Dot Mode)

Typical Applications

This application shows that the LED supply requires minimal filtering.

*See Application Hints for optional Peak or Average Detector.

Adjust R3 for 3 dB difference between LED #11 and LED #12

†

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LM3916

00797123

Extended Range VU Meter (Dot Mode)

Typical Applications (Continued)

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D1, D2: 1N914 or 1N4148

*OPTIONAL SHUNTS 100 µA auxiliary sink current away from LED #1.

See Application Hints for optional peak or average detector.

†

Typical Applications (Continued)

Driving Vacuum Fluorescent Display

LM3916

R7 thru R15: 10k±10%

D1, D2: 1N914 or 1N4148

*Half-wave peak detector.

See Application Hints.

00797124

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Typical Applications (Continued)

LM3916

*The input to the Dot-Bar switch may be taken from cathodes of other LEDs. Display will change to bar as soon as the LED so selected begins to light.

**Optional. Shunts 100 µA auxiliary sink current away from LED #1.

Indicator and Alarm, Full-Scale Changes Display From Dot to Bar

00797125

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00797126

LM3916

High Resolution VU Meter (Bar Mode)

Typical Applications (Continued)

*See Application Hints for optional peak or average detector.

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LM3916

00797127

High Resolution VU Meter (Dot Mode)

Typical Applications (Continued)

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*Optional shunts 100 µA auxiliary sink current away from LED #1.

See Application Hints for optional peak or average detector.

†

Typical Applications (Continued)

LM3916

Displaying Additional Levels

00797128

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Typical Applications (Continued)

LM3916

The LED currents are approximately 10 mA, and LM3916 outputs operate in saturation for minimum dissipation.

*This point is partially regulated and decreases in voltage with temperature. Voltage requirements of the LM3916 also decrease with temperature.

Operating with a High Voltage Supply (Dot Mode Only)

00797129

Low Current Bar Mode Display

Supply current drain is only 20 mA with ten LEDs illuminated@16 mA.

00797130

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Typical Applications (Continued)

LM3916

Driving Liquid Crystal Display

00797131

Bar Display with Alarm Flasher

Full-scale causes the full bar display to flash. If the junction of R1 and C1 is connected to a different LED cathode, the display will flash when that LED lights,
and at any higher input signal.

00797132

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Connection Diagram

LM3916

Dual-In-Line Package

Order Number LM3916N-1

See NS Package Number NA18A

Order Number LM3916N *

See NS Package Number N18A

*Discontinued, Life Time Buy date 12/20/99

Definition of Terms

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

Comparator Gain: The ratio of the change in output current

) to the change in input voltage (VIN) required to pro-

(I

LED

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

Top View

00797133

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 (V

+

).

(V

) over the specified range of supply voltage

REF

Load Regulation: The change in reference output voltage
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

) equal to pin 4 voltage (V

RHI

RLO

).

Relative Accuracy: The difference between any two adja­cent threshold points. Specified and tested with 10V across
the internal voltage divider so that resistor ratio matching
error predominates over comparator offset voltage.

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Physical Dimensions inches (millimeters) unless otherwise noted

LM3916

Note: Unless otherwise specified.

1. Standard Lead Finish:

200 microinches /5.08 micrometer minimum

lead/tin 37/63 or 15/85 on alloy 42 or equivalent or copper

2. Reference JEDEC registration MS-001, Variation AC, dated May 1993.

Molded Dual-In-Line Package (N)

Order Number LM3916N-1

NS Package Number NA18A

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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

LM3916 Dot/Bar Display Driver

Molded Dual-In-Line Package (N)

Order Number LM3916N *

NS Package Number N18A

*Discontinued, Life Time Buy date 12/20/99

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.

For the most current product information visit us at www.national.com.

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