LM2794/95

2.7 - 5.5V

1 …F

(3/2)x

Charge Pump

GND

1 …F

SD

1 …F

1 …F

Voltage

Reference

Brightness

Control

BRGT

*(Only on

LM2795)

10PA

*

110 k:

130 k:

330 k:

LM2794, LM2795

SNVS168K – MAY 2004 – REVISED MAY 2004

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Functional Block Diagram

Application Information

CIRCUIT DESCRIPTION

The LM2794/5 is a 1.5x/1x CMOS charge pump with four matched constant current outputs, each capable of

driving up to 20mA through White LEDs. This device operates over the extended Li-Ion battery range from 2.7V

to 5.5V. The LM2794/5 has four regulated current sources connected to the device's 1.5x charge pump output

or above 4.7V (typ.). The device can drive up to 80mA through any combination of LEDs connected to the

reference current is then multiplied and mirrored to each constant current output. The LED brightness can then

be controlled by analog and/or digital methods. Applying an analog voltage in the range of 0V to 3.0V to the

Brightness pin (BRGT) adjusts the dimming profile of the LEDs. The digital technique uses a PWM (Pulse Width

SOFT START

Soft start is implemented internally by ramping the reference voltage more slowly than the applied voltage.

During soft start, the current through the LED outputs will ramp up in proportion to the rate that the reference

voltage is being ramped up.

SHUTDOWN MODE

The shutdown pin (SD) disables the part and reduces the quiescent current to 2.3µA (typ.).

The LM2795 has an active-high shutdown pin (HIGH = shutdown, LOW = operating). An internal pull-up is

shutdown, as shown in Figure 2. The LM2795 SD pin can also be driven with a rail-to-rail CMOS logic signal.

8

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