LM3914 NATIONAL SEMICONDUCTOR User's Manual

February

LM ot/B ar isplay river

LM3914 Dot/Bar Display Driver

Much of the display flexibility derives from the fact that all

General Description

outputs are individual, DC regulated currents. Various effects

The LM3914 is monolithic integrated circuit that senses

can be achieved by modulating these currents. The indi-

analog voltage levels and drives LEDs, providing linear

vidual outputs can drive transistor as well as LED at the

analog display. single pin changes the display from

same time, so controller functions including “staging” control

moving dot to bar graph. Current drive to the LEDs is

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

regulated and programmable, eliminating the need for resis-

mer, or sequencer.

tors. This feature is one that allows operation of the whole

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

system from less than 3V.

LM3914N-1 is available in an 18-lead molded (N) package.

The circuit contains its own adjustable reference and accu-

The following typical application illustrates adjusting of the

rate 10-step voltage divider. The low-bias-current input

reference to desired value, and proper grounding for ac-

buffer accepts signals down to ground, or V−, yet needs no

curate operation, and avoiding oscillations.

protection against inputs of 35V above or below ground. The buffer drives individual comparators referenced to the

precision divider. Indication non-linearity can thus be held Features

typically to even over wide temperature range. Drives LEDs, LCDs or vacuum fluorescents

Versatility was designed into the LM3914 so that controller, Bar or dot display mode externally selectable by user

visual alarm, and expanded scale functions are easily added Expandable to displays of steps on to the display system. The circuit can drive LEDs of many Internal voltage reference from 1.2V to 12V colors, or low-current incandescent lamps. Many LM3914s

Operates with single supply of less than 3V

can be “chained” to form displays of to over seg-

Inputs operate down to ground

ments. Both ends of the voltage divider are externally avail-

Output current programmable from m A to m A

able so that drivers can be made into zero-center meter.

No multiplex switching or interaction between outputs

The LM3914 is very easy to apply as an analog meter circuit.

Input withstands ±35V without damage or false outputs

1.2V full-scale meter requires only resistor and single

LED driver outputs are current regulated,

3V to 15V supply in addition to the display LEDs. If the

open-collectors

resistor is pot, it becomes the LED brightness control. The

Outputs can interface with TTL or CMOS logic

simplified block diagram illustrates this extremely simple

external circuitry. The internal 10-step divider is floating and can be referenced to wide range of voltages

When in the dot mode, there is small amount of overlap or “fade” (about m V) between segments. This assures that at no time will all LEDs be “OFF”, and thus any ambiguous display is avoided. Various novel displays are possible.

National Semiconductor Corporation DS007970 www.national.com