LM3914N Datasheet

IC型号：
LM3914N
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National Semiconductor [Dot/Bar Display Driver]
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LM3914 Dot/Bar Display Driver

January 2000

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

鈭?/div>

, 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

鈦?/div>

%, 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 鈥渃hained鈥?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

鈥渇ade鈥?(about 1 mV) between segments. This assures that at

no time will all LEDs be 鈥淥FF鈥? 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 鈥渟taging鈥?control

can be performed. The LM3914 can also act as a program-

mer, or sequencer.

The LM3914 is rated for operation from 0藲C to +70藲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

卤

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

漏 2000 National Semiconductor Corporation

DS007970

www.national.com

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