SP6685ER datasheet(6/10 Pages) SIPEX

6 / 10 page

Date: 12/15/04

SP6685 Charge Pump LED Driver for Camera Flash

FUNCTIONAL DIAGRAM

The SP6685 is a charge pump regulator

designed for converting a Li-Ion battery

voltage of 2.7V to 4.2V to drive a white LED

used in digital still camera Flash and Torch

applications. The SP6685 has two modes

of operation which are pin selectable for

either Flash or Torch. Flash mode is usually

used with a pulse of about 200 to 300

milliseconds to generate a high intensity

Flash. Torch can be used continuously at a

lower output current than Flash and is often

used for several seconds in a digital still

camera “movie” mode.

The SP6685 also has two modes of opera-

tion to control the output current, the 1X

mode and 2X mode. Operation begins after

the enable pin EN receives a logic high, the

bandgap reference wakes up after 200µsec,

and then SP6685 goes through a soft-start

mode designed to reduce inrush current.

The SP6685 starts in the 1X mode, which

acts like a linear regulator to control the

output current by continuously monitoring

the feedback pin FB. In 1X mode, if the

SP6685 auto detects a dropout condition,

which is when the FB pin is below the

THEORY OF OPERATION

RSET BLOCK

RSET

{1.26V

RSET

}

x11.2kohms

1.25V

BG REF

RSET REF

RESISTOR

TAPS

50mV

FLASH

FLASH=1, S=1, RSET REF

FLASH=0, S=0, 50mV

0 s

MUX

2x1

FB REF

SGN 8

COM P

FB COMP

CLR

COUNTER

32 COUNT

ONE

SHOT

SET

DOMIANT

MODE SWITCH

0 =1X

1=2X

VIN

135C ON

145C OFF

THERMAL FAULT

OVER TEMP COMP

CLK

2.4MHZ

CHARGE

PUMP

SWITCHES

PGND

VOUT

CLK

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