Datasheet LM3916N-1 Datasheet (NSC)

LM3916
Dot/Bar Display Driver

LM3916 Dot/Bar Display Driver

January 2000

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 dotdisplay. LED current drive isregulated
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 precisiondivider. Accuracyistypi­cally 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-

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

© 2000 National Semiconductor Corporation DS007971 www.national.com

Typical Applications

LM3916

0V to 10V VU Meter

DS007971-1

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

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
Lead Temperature

(Soldering, 10 seconds) 260˚C

Electrical Characteristics (Notes 2, 4)

Parameter Conditions (Note 2) Min Typ Max Units
COMPARATORS

Offset Voltage, Buffer and First Comparator 0V ≤ V

I

LED

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

I

LED

Gain (∆I

/ ∆VIN)I

LED

(REF)

Input Bias Current (at Pin 5) 0V ≤ V
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

−10 dB ≤ V

Absolute Accuracy (Note 3)

V

IN

V

IN

V

IN

VOLTAGE REFERENCE

Output Voltage 0.1 mA ≤ I

+

=

V
Line Regulation 3V ≤ V
Load Regulation 0.1 mA ≤ I

Output Voltage Change with Temperature 0˚C ≤ T

+

=

V

+

=

V
Adjust Pin Current 75 120 µA

OUTPUT DRIVERS

+

V

V

=

LED
LED

LED Current V
LED Current Difference (Between Largest and

Smallest LED Currents)
LED Current Regulation 2V ≤ V

I

LED

I

LED

Dropout Voltage I

Saturation Voltage I

LED(ON)

∆I

LED

LED

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

=

≤ 12V,

V

RLO

=

1mA

RLO

=

1mA

=

IN

=

2, 1, 0, −1 dB

=

−3, −5 dB

=

−7, −10, −20 dB

V

LED
+

V

LED

V

LED

V

LED

=
=

LED

2mA
=

20 mA

=

=

2.0 mA, I

=

2 mA, I

RHI

≤ 12V,

V

RHI

=

10 mA 3 8 mA/mV

LED

310 mV

315 mV

≤ (V+−1.5V) 25 100 nA

≤ 3dB

IN

≤ −1 dB

IN

IN

L(REF)

=

5Vg

≤ −7 dB

≤ 4 mA,

0.75

1.5

2.5

−0.25

−0.5

−1

1.0

2.0

3.0

1.25

2.5

2.5

+0.25

+0.5

+1

1.2 1.28 1.34 V

≤ 18V 0.01 0.03

≤ 4 mA,

L(REF)

=

5V

≤ +70˚C, I

A

=

5V

= 5V, I

5V, I

LED

5V, I

LED

L(REF)

=

2mA

=

20 mA

=

L(REF)

1 mA,

=

1 mA 7 10 13 mA

0.4 2

1

0.12

1.2

0.4
3

≤ 17V

0.110.25
3

=

20 mA

2mA

L(REF)

=

@

V

5V,

LED

=

0.4 mA 0.15 0.4 V

1.5 V

dB
dB
dB

dB
dB
dB

%

mA
mA

mA
mA

/V

%

%

+

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Electrical Characteristics (Notes 2, 4) (Continued)

LM3916

Parameter Conditions (Note 2) Min Typ Max Units
SUPPLY CURRENT

+

Standby Supply Current
(All Outputs Off)

Note 1: AbsoluteMaximum 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

3V

≤ V

LED

RHI

≤ V

≤ 12 V

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

abled 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).

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

.

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

=

V

+ 5V, I

+

=

+ 20V, I

V

=

T

25˚C, I

A

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

DC

L(REF)

=

L(REF)

=

0.2 mA

=

L(REF)

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

1.0 mA

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

⁄

4

8.660 8.913 9.173 −5

1

±

1

⁄

4

7.718 7.943 8.175 −7±1 2.818 3.162 3.548

1

±

0

⁄

4

6.879 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

±

⁄

2

4.732 5.012 5.309

1

±

⁄

2

3.548 3.981 4.467

Volts

mA
mA

Typical Performance Characteristics

Supply Current vs
Temperature

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Operating Input Bias
Current vs Temperature

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Reference Voltage vs
Temperature

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Typical Performance Characteristics (Continued)

LM3916

Reference Adjust Pin
Current vs Temperature

Input Current Beyond
Signal Range (Pin 5)

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LED Current-Regulation
Dropout

LED Current vs
Referenced Loading

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LED Driver Saturation
Voltage

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LED Driver Current
Regulation

Total Divider Resistance
vs Temperature

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Common-Mode Limits

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Output Characteristics

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Block Diagram (Showing Simplest Application)

LM3916

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LM3916

Functional Description

The simplified LM3916 block diagram is included 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 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:

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

0.05 µF.

+

and no lower than V−.

DS007971-5

+

and load changes. For

LM3916 Output Circuit

DS007971-6

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 the

E

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)

+

3(V

pin).

directly

to pin

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

).

Mode Pin Functional Description

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

Block Diagram of Mode Pin Function

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
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.

*

High for bar

DS007971-7

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Mode Pin Functional Description

(Continued)

LM3916

DOT OR BAR MODE SELECTION

The voltage at pin 9 is sensed by comparator C1, nominally
referenced to (V
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
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 display to make sense when multiple drivers are
cascaded in dot mode, special circuitry has been included to
shut off LED
ond device comes on. The connection for cascading in dot
mode has already been described and is depicted in

1

.

As long as the input signal voltage is below the threshold of
the second driver,LED
effectively an open circuit so the chip is in dot mode.As soon

+

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

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

+

(bar mode). In bar mode,

#

10 of the first device when LED#1 of the sec-

#

11is off. Pin 9 of driver#1 thus sees

Figure

#

as the input voltage reaches the threshold of LED
of driver
V
enced 600 mV below V

#

1 is pulled an LED drop (1.5V or more) below

. This condition is sensed by comparator C2, refer-

LED

. This forces the output of C2 low,

LED

which shuts off output transistor Q2, extinguishing LED
V

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

LED

11,pin 9

#

10.

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

#

LED

1) with a 10k resistor. The 1V 1R drop is more than the
900 mV worst case required to hold off LED
enough that LED

#

11 does not conduct significantly.

#

11(and

#

10 yet small

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
through two series-connected diodes as shown in

LED

Figure 2

Shunting the diodes with a 1k resistor provides a path for
driver leakage current.

.

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

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

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Mode Pin Functional Description

(Continued)

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 overa1mVrange. The change may be much
more rapid between LED

second

device cascaded.

#

10 of one device and LED#1ofa

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
cillations. 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.

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.

to LED anode common can cause os-

LED

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 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.

DS007971-10

*

DC Couple

FIGURE 3. Half-Wave Peak Detector

LM3916

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

±

up to

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

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Application Hints (Continued)

LM3916

D1, D2: 1N914 or 1N4148

Average Peak

R2 1k 100k
R3 100k 1k

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

For precision full-wave averaging use the circuit in
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
ror when the input is a nonsymmetrical transient). The aver­aging time constant is R5
in the precision full-wave detector of
capacitor is not buffered, this circuit can drive only high im­pedance loads such as the input of an LM3916.

=

1

V

=

10

V

FIGURE 4. Precision Half-Wave Rectifier

C2. A simple modification results

•

Figure 6

. Since the filter

DS007971-11

Figure 5

±

DS007971-12

D1, D2: 1N914 or 1N4148

FIGURE 5. Precision Full-Wave Average Detector

.

1dBer-

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DS007971-13

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 under­damped second order response with a resonant frequency
of2.1HzandaQof0.62.

Figure 7

depicts a simple rectifier/

filter circuit that meets these criteria.

Application Hints (Continued)

Design Equations

LM3916

DS007971-14

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 fora5msburstand are met by an attack
time constant of 1.7 ms.

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
grounded, runs at 1.25V full-scale. R1 and R2 set the
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 ob-

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

threshold of LED
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

Figure 5

#

1 on the LM3915 is only 56 mV. Since

, is to keep the reference the same for

. The LM3915, with pin 8

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Application Hints (Continued)

both drivers (10V in the example) and

LM3916

nal by 16 dB ahead of the LM3915. Alternatively, instead of

≅

V

7.89V

REF2

amplify

the input sig-

amplifying, input signals of sufficient amplitude can be fed di­rectly to the LM3916 and

attenuated

by 16 dB to drive the

LM3915.

DS007971-15

FIGURE 8. Low Cost Circuit for 40 dB Display

FIGURE 9. Improved Circuit for 40 dB Display

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

DS007971-16

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

www.national.com 12

Application Hints (Continued)

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. Totrim the reference voltage, vary R2.

The current in
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.

FIGURE 10. Design Equations for Fixed LED Intensity

Figure 11

REF

=

shows how to add a LED intensity

5V lowers the current drawn by the ladder,

DS007971-17

DS007971-18

5mA≤I

≤ 28 mA@V

LED

REF

=

5V

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

The scheme in

REF

=

5V.

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.

LM3916

www.national.com13

Application Hints (Continued)

LM3916

5mA≤I
V

REF

≤ 28 mA

LED

=

5V

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

DS007971-19

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

www.national.com 14

DS007971-20

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.

Other Applications (Continued)

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

LM3916

DS007971-21

www.national.com15

Typical Applications

LM3916

DS007971-22

Extended Range VU Meter (Dot Mode)

See Application Hints for optional Peak or Average Detector.

*

This application shows that the LED supply requires minimal filtering.

12

#

11 and LED

#

Adjust R3 for 3 dB difference between LED

†

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Typical Applications (Continued)

LM3916

DS007971-23

Extended Range VU Meter (Dot Mode)

1.

#

OPTIONAL SHUNTS 100 µA auxiliary sink current away from LED

*

D1, D2: 1N914 or 1N4148

See Application Hints for optional peak or average detector.

†

www.national.com17

Typical Applications (Continued)

LM3916

Driving Vacuum Fluorescent Display

R7 thru R15: 10k±10
D1, D2: 1N914 or 1N4148

*

Half-wave peak detector.

See Application Hints.

www.national.com 18

%

DS007971-24

Typical Applications (Continued)

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

DS007971-25

*

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.

LM3916

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Typical Applications (Continued)

LM3916

DS007971-26

High Resolution VU Meter (Bar Mode)

See Application Hints for optional peak or average detector.

*

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Typical Applications (Continued)

LM3916

DS007971-27

High Resolution VU Meter (Dot Mode)

1.

#

Optional shunts 100 µA auxiliary sink current away from LED

*

See Application Hints for optional peak or average detector.

†

www.national.com21

Typical Applications (Continued)

LM3916

Displaying Additional Levels

DS007971-28

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Typical Applications (Continued)

Operating with a High Voltage Supply (Dot Mode Only)

LM3916

DS007971-29

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.

Low Current Bar Mode Display

DS007971-30

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

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Typical Applications (Continued)

LM3916

Driving Liquid Crystal Display

DS007971-31

Bar Display with Alarm Flasher

DS007971-32

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.

www.national.com 24

Connection Diagram

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
(I

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

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

DS007971-33

*

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.

LM3916

www.national.com25

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, VariationAC, dated May 1993.

Molded Dual-In-Line Package (N)

Order Number LM3916N-1

NS Package Number NA18A

www.national.com 26

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

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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the

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
the life support device or system, or to affect its
safety or effectiveness.

labeling, can be reasonably expected to result in a
significant injury to the user.

National Semiconductor
Corporation

Americas
Tel: [phone]
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www.national.com

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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