Copyright © 2016, Texas Instruments Incorporated

Gain Control

1x, 1.5x

Charge Pump

Current

Control

Flash, Torch

Mode

Control

OSC

Ind.

Torch

Flash

EN1

EN2

LED

1 µF

C1+

C1-

C2+

C2-

GND

1 µF

LED

-

7

LM2758

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SNVS551E – APRIL 2008 – REVISED MAY 2016

Product Folder Links: LM2758

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Copyright © 2008–2016, Texas Instruments Incorporated

7 Detailed Description

7.1 Overview

The LM2758 is an adaptive 1× and 1.5× CMOS charge pump, optimized for driving flash LEDs in camera phones

and other portable applications. It provides a constant current of 500 mA (typical) for flash mode and 107 mA

There are four modes of operation for LM2758: the flash mode, torch mode, indicator mode, and shutdown mode

(see Table 1). Torch and flash modes sink a constant DC current while indicator mode operates in pulsating DC

for the current sink to drive desired current through LED.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Charge Pump and Gain Transitions

voltage is approximately equal to the input voltage. When input voltage is over 4.7 V the output voltage is

regulated to 4.7 V. In 1.5× mode, the output voltage is always less than or equal to 4.7 V over entire input

voltage range.

The gain of the charge pump is selected depending on the headroom voltage across the current sink of LM2758.

happens from 1× to 1.5× to maintain current regulation across the LED. Once the charge pump transition to a

higher gain, it remains at that gain for as long as the device remains enabled. Shutting down and then re-

enabling the device resets the gain mode to the minimum gain required to maintain the load.