LM2794/LM2795

Current Regulated Switched Capacitor LED Supply with

Analog and PWM Brightness Control

General Description

The LM2794/95 is a fractional CMOS charge-pump that

provides four regulated current sources. It accepts an input

voltage range from 2.7V to 5.5V and maintains a constant

current determined by an external sense resistor.

The LM2794/5 delivers up to 80mA of load current to accom-

modate four White LEDs. The switching frequency is

325kHz. (min.) to keep the conducted noise spectrum away

from sensitive frequencies within portable RF devices.

Brightness can be controlled by both linear and PWM tech-

niques. A voltage between 0V and 3.0V may be applied to

the BRGT pin to linearly vary the LED current. Alternatively,

a PWM signal can be applied to the SD pin to vary the

perceived brightness of the LED. The SD pin reduces the

operating current to 2.3µA (typ.) The LM2794 is shut down

when the SD pin is low, and the LM2795 is shut down when

the SD pin is high.

The LM2794/95 is available in a micro SMD-14 CSP pack-

age.

Features

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between any two outputs

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High efficiency 3/2 boost function

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Drives one, two, three or four white LEDs

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2.7V to 5.5V Input Voltage

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Up to 80mA output current

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Analog brightness control

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Active-low or high shutdown input (’94/95)

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Very small solution size and no inductor

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2.3µA (typ.) shutdown current

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325kHz switching frequency (min.)

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Constant Frequency generates predictable noise

spectrum

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Standard Micro SMD-14 package: 2.08mm X 2.403mm

X 0.845mm High

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Thin Micro SMD-14 package: 2.08mm X 2.403mm X

0.600mm High

Applications

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White LED Display Backlights

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White LED Keypad Backlights

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1-Cell Li-Ion battery-operated equipment including

PDAs, hand-held PCs, cellular phones

Basic Application Circuit

20028503

March 2004

© 2004 National Semiconductor Corporation

DS200285

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