lm3915

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 analog 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 Iow 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 ±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 dynamie rangę, 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, morę 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 morę 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 modę display with a rangę 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 meter.

Features

■ 3 dB/step, 30 dB rangę

■ Drives LEDs, LCDs, or vacuum fluorescents

■ Bar or dot display modę externally selectable by user

■ Expandable to displays of 90 dB

■ Internal voltage reference from 1.2V to 12V

■ Operates with single supply of 3V to 25V

■ Inputs operate down to ground

■ Output current programmable from 1 mA to 30 mA

■ Input withstands ±35V without damage or false outputs

■ Outputs are current regulated, open collectors

■ Directly drives TTL or CMOS

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

The LM3915 is rated for operation from 0°C to + 70°C. The LM3915N is available in an 18-lead molded DIP package.

0V to 10V Log Display

O 3V''."V, <:V“

Typical Applications

LM3915

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REF

OUT

REF

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C1 2.2 fiF

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12V TO 20V

Vref

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t R2 x 80 juA

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2.2 kii

SIGNAL

SOURCE

Notę 1: Capacitor C1 is re-quired if leads to tl>e LED supply are 6" or longer.

Notę 2: Circuit as shown is wired for dot modę. For bar modę, connect pin 9 to pin 3. Vled must be kept below 7V or dropping resistor should be used to limit IC power dissipa-tion.

TL/H/5104-1

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