lm3915n.pdf

February 1995

LM3915 Dot/Bar Display Driver

General Description

The LM3915 is a monolithic integrated circuit that senses

analog voltage levels and drives ten LEDs, LCDs or vacuum

fluorescent displays, providing a logarithmic 3 dB/step ana-

log display. 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 re-

sistors. 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 ac-

curate 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 g 35V. The input buffer drives 10 individual

comparators referenced to the precision divider. Accuracy is

typically better than 1 dB.

The LM3915's 3 dB/step display is suited for signals with

wide dynamic range, such as audio level, power, light inten-

sity or vibration. Audio applications include average or peak

level indicators, power meters and RF signal strength me-

ters. 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 LM3915 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.

The LM3915 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 with a range of 60 or 90 dB.

LM3915s can also be cascaded with LM3914s for a linear/

log display or with LM3916s for an extended-range VU me-

ter.

Features

Y 3 dB/step, 30 dB range

Y Drives LEDs, LCDs, or vacuum fluorescents

Y Bar or dot display mode externally selectable by user

Y Expandable to displays of 90 dB

Y Internal voltage reference from 1.2V to 12V

Y Operates with single supply of 3V to 25V

Y Inputs operate down to ground

Y Output current programmable from 1 mA to 30 mA

Y Input withstands g 35V without damage or false outputs

Y Outputs are current regulated, open collectors

Y Directly drives TTL or CMOS

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

enced to a wide range of voltages

The LM3915 is rated for operation from 0 § Cto a 70 § C. The

LM3915N is available in an 18-lead molded DIP package.

Typical Applications

0V to 10V Log Display

Note 1: Capacitor C1 is re-

quired if leads to the LED sup-

ply are 6 × or longer.

Note 2: Circuit as shown is

wired for dot mode. For bar

V REF e 1.25V

1 a

a R2x80 m A

mode, connect pin 9 to pin 3.

V LED must be kept below 7V or

dropping resistor should be

12.5V

R1 a

V REF

2.2 k X

I LED e

used to limit IC power dissipa-

tion.

TL/H/5104±1

C 1995 National Semiconductor Corporation

TL/H/5104

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

Absolute Maximum Ratings

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales

Office/Distributors for availability and specifications.

Power Dissipation (Note 5)

Molded DIP(N)

Input Signal Overvoltage (Note 3)

g 35V

Divider Voltage

b 100 mV to V a

Reference Load Current

10 mA

1365 mW

Storage Temperature Range

b 55 § Cto a 150 § C

Lead Temperature (Soldering, 10 sec.)

260 § C

Supply Voltage

25V

Voltage on Output Drivers

25V

Electrical Characteristics (Notes 1 and 3)

Parameter

Conditions (Note 1)

Min Typ Max Units

Comparators

Offset Voltage, Buffer and First

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

Comparator

I LED e 1mA

Offset Voltage, Buffer and Any Other

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

Comparator

I LED e 1mA

Gain ( D I LED / D V IN )

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

mA/mV

Input Bias Current (at Pin 5)

0V s V IN s (V a b 1.5V)

100

Input Signal Overvoltage

No Change in Display

b 35

Voltage-Divider

Divider Resistance

Total, Pin 6 to 4

k X

Relative Accuracy (Input Change

(Note 2)

2.0

3.0

4.0

Between Any Two Threshold Points)

Absolute Accuracy at Each Threshold Point

(Note 2)

V IN eb 3, b 6dB

b 0.5

a 0.5

V IN eb 9dB

b 0.5

a 0.65

V IN eb 12, b 15, b 18 dB

b 0.5

a 1.0

V IH eb 21, b 24, b 27 dB

b 0.5

a 1.5

Voltage Reference

Output Voltage

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

1.2 1.28 1.34

V a e V LED e 5V

Line Regulation

3V s V a s 18V

0.01 0.03 %/V

Load Regulation

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

0.4

2 %

V a e V LED e 5V

Output Voltage Change with Temperature

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

V a e V LED 5V

Adjust Pin Current

120

m A

Electrical Characteristics (Note 1) (Continued)

Parameter

Conditions (Note 1)

Min Typ Max Units

Output Drivers

LED Current

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

13 mA

LED Current Difference (Between Largest V LED e 5V, I LED e 2 mA

0.12

0.4 mA

and Smallest LED Currents)

V LED e 5V, I LED 20 mA

1.2

LED Current Regulation

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

0.1

0.25 mA

I LED e 20 mA

Dropout Voltage

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

1.5

D I LED e 2mA

Saturation Voltage

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

0.15

0.4

Output Leakage, Each Collector

Bar Mode (Note 4)

0.1

m A

Output Leakage

Dot Mode (Note 4)

Pins 10-18

0.1

m A

Pin 1

150

450

m A

Supply Current

Standby Supply Current

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

2.4

4.2 mA

(All Outputs Off)

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

6.1

9.2 mA

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

3VDC s V a s 20 VDC b 0.015V s VRLO s 12 VDC TA e 25 § C, IL(REF) e 0.2 mA, pin 9 connected to pin 3 (bar mode).

3V DC s V LED s V a V REF ,V RHI ,V RLO s (V a b 1.5V) For higher power dissipations, pulse testing is used.

b 0.015V s V RHI s 12 V DC 0V s V IN s V a b 1.5V

Note 2: Accuracy is measured referred to 0 dB ea 10.000 V DC at pin 5, with a 10.000 V DC at pin 6, and 0.000 V DC at pin 4. At lower full scale voltages, buffer

and comparator offset voltage may add significant error. See table for threshold voltages.

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

Note 4: Bar mode results when pin 9 is within 20 mV of V a . Dot mode results when pin 9 is pulled at least 200 mV below V a . LED Ý10 (pin 10 output current) is

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

Note 5: The maximum junction temperature of the LM3915 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).

THRESHOLD VOLTAGE (Note 2)

Output

Min

Typ Max Output

Min

Typ

Max

1 b 27

0.422

0.447

0.531

6 b 12

2.372

2.512

2.819

2 b 24

0.596

0.631

0.750

b 9

3.350

3.548

3.825

3 b 21

0.841

0.891

1.059

b 6

4.732

5.012

5.309

4 b 18

1.189

1.259

1.413

b 3

6.683

7.079

7.498

5 b 15

1.679

1.778

1.995

9.985

10.015

Typical Performance Characteristics

Supply Current vs

Operating Input Bias

Reference Voltage vs

Temperature

Current vs Temperature

Temperature

Reference Adjust Pin

LED Current-Regulation

LED Driver Saturation

Current vs Temperature

Dropout

Voltage

Input Current Beyond

LED Current vs

LED Driver Current

Signal Range (Pin 5)

Reference Loading

Regulation

TL/H/5104±2

Total Divider Resistance

vs Temperature

Common-Mode Limits

Output Characteristics

TL/H/5104±3

Block Diagram (Showing Simplest Application)

TL/H/5104±4

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