SP6685_06 Datasheet, PDF (11/16 Pages) Sipex Corporation – 700mA Buck/Boost Charge Pump LED Driver

FUNCTIONAL DIAGRAM
RSET 6
RSET
RSET BLOCK
+
-
{ } ^1.26V
V= _{RSET x11.2kohms}
RSET REF
BG REF
+
-
1.26V
RESISTOR
TAPS
50mV
1 _MUX
2x1
0s
FB REF
FB 7
+
FB
- ^{COM P}
SGN 8
CLK
FB COMP
COUNTER
32 COUNT
CLR
ONE
SHOT
FLASH 4
FLASH=1, S=1, RSET REF
FLASH=0, S=0, 50mV
EN 5
VIN 1
135C ON
145C OFF
THERMAL FAULT
OVER TEMP COMP
2.4MHZ
CLK
MODE SWITCH
0 =1X
1=2X
CHARGE
PUMP
SWITCHES
C1
C2
VOUT
CLK
SET
DOMINANT
S
0
R
PGND
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
THEORY OF OPERATION
SP6685 auto detects a dropout condition,
which is when the FB pin is below the
regulation point for more than 32 cycles of
the internal clock, the SP6685 automati-
cally switches to the 2X mode. The SP6685
remains in the 2X mode until one of four
things happens: 1) the enable pin EN has
been toggled, 2) the Flash pin has changed
from high to low, 3) V_IN is cycled or, 4) a
thermal fault occurs.
The 2X mode is the charge pump mode
where the output can be pumped as high as
two times the input voltage, provided the
output does not exceed the maximum volt-
age for the SP6685, which is internally
limited to about 5.5V. In the 2X mode, as in
the 1X mode, the output current is regulated
by the voltage at the FB pin.
In the Torch mode, (Flash = GND) the Flash
pin is set to logic low and the SP6685 FB pin
regulates to 50mV output:
V_FB = 50mV (Torch Mode)
Date: 7/6/06 Rev B
SP6685, 700mA Buck/BoostCharge Pump LED Driver
11
© 2006 Sipex Corporation