FUNCTIONAL DIAGRAM
CLK
RSET BLOCK
COUNTER
32 COUNT
RSET REF
FB REF
FB
1
0
MUX
2x1
s
6
SET
RSET
+
-
+
-
FB COMP
FB
COM
CLR
DOMIANT
RESISTOR
TAPS
P
50mV
BG REF
7
S
0
RSET
+
1.25V
-
SGN
8
ONE
1.26V
SHOT
V=
R
}
{
RSET
x11.2kohms
FLASH
4
EN
5
FLASH=1, S=1, RSET REF
FLASH=0, S=0, 50mV
VIN
1
MODE SWITCH
0 =1X
1=2X
135C ON
145C OFF
THERMAL FAULT
OVER TEMP COMP
C1
CHARGE
PUMP
C2
SWITCHES
VOUT
2.4MHZ
CLK
CLK
PGND
THEORY OF OPERATION
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
bandgapreferencewakesupafter200µsec,
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
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
eitherFlashorTorch. Flashmodeisusually
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.
Date: 12/15/04
SP6685 Charge Pump LED Driver for Camera Flash
© Copyright 2004 Sipex Corporation
6
SIPEX [ SIPEX CORPORATION ]
