LM2791

SNVS156M – FEBRUARY 2001 – REVISED MAY 2013

www.ti.com

CIRCUIT DESCRIPTION

The LM2791 provides two matched current sources for driving high forward voltage drop LEDs from Li-Ion

battery sources. The device has on-chip current regulators which are composed of current mirrors with a 25 to 1

ratio. The mirrors control the LED current without using current limiting resistors in the LED current path. The

device can drive up to a total of 36mA through the LEDs.

The LED brightness can be controlled by both analog and or digital methods. The digital technique uses a PWM

(Pulse Width Modulation) signal applied to the shutdown input. The analog technique applies an analog voltage

to the brightness (BRGT) pin (see Application Information). For lowest cost, the LM2791 can be used for

constant brightness by grounding BRGT and enabling the shutdown pin.

APPLICATION INFORMATION

SOFT START

LM2791 includes a soft start function to reduce the inrush currents and high peak current during power up of the

device. Soft start is implemented internally by ramping the bandgap more slowly than the applied voltage. This is

done by holding the bandgap in shutdown for a short time. During soft start, the switch resistances limit the

inrush current used to charge the flying and hold capacitors.

SHUTDOWN MODE

A shutdown pin (SD or /SD) is available to disable the LM2791 and reduce the quiescent current to 1µA

maximum. The LM2791 is available with both senses of shutdown polarity.

During normal operation mode of the "-L" options, an active high logic signal to the SD pin or tying the SD pin to

During normal operation mode of the "-H" options, an active low logic signal to the SD pin or tying the SD pin to

CAPACITOR SELECTION

recommended for this application. Table 1 below lists suggested capacitor suppliers for the typical application

circuit.

8

Submit Documentation Feedback

Copyright © 2001–2013, Texas Instruments Incorporated

Product Folder Links: LM2791

Not Recommended For New Designs