POWER MANAGEMENT
1
SC621
LED Light Management Unit
Charge Pump, 4 LEDs, 400mA Flash LED,
Dual LDOs, and SemWire
TM
Interface
© 2009 Semtech Corporation
Features
Input supply voltage range — 3.0V to 5.5V
Charge pump modes — 1x, 1.5x and 2x
Four programmable current sinks with 32 steps from
0.5mA to 25mA
Flash LED — 400mA max in ash mode, 250mA max
continuous for spotlight
Two programmable 200mA low-noise LDO regulators
Charge pump frequency — 250kHz
SemWire
TM
single wire interface — up to 75kbit/s
Backlight current accuracy ±1.5% typical
Backlight current matching ±0.5% typical
Programmable fade-in/fade-out for main backlight
External ash control pin to sync with camera
Optional 1s ash time out
Automatic sleep mode (LEDs o ) — I
Q
= 100μA
Low shutdown current — 0.1μA (typical)
Ultra-thin package — 3mm x 3mm x 0.6mm
Lead-free and halogen-free
WEEE and RoHS compliant
Applications
Cellular phone backlighting and ash
PDA backlighting and ash
Camera I/O and core power
Description
The SC621 is a high e ciency charge pump LED driver
using Semtech’s proprietary mAhXLife
TM
technology.
Performance is optimized for use in single-cell Li-ion
battery applications.
The charge pump provides backlight current in
conjunction with four matched current sinks. It also can
supply continuous or bursted current to a ash LED using
the dedicated ash driver current sink. The load and
supply conditions determine whether the charge pump
operates in 1x, 1.5x, or 2x mode. An optional fading feature
that gradually adjusts the backlight current is provided to
simplify control software. A ash-timeout feature disables
the ash if active for longer than 1 second. The SC621 also
provides two low-dropout, low-noise linear regulators for
powering a camera module or other peripheral circuits.
The SC621 uses the proprietary SemWire
TM
single wire
interface. The interface controls all functions of the
device, including backlight and ash currents as well as
two LDO voltage outputs. The single wire implementation
minimizes microcontroller and interface pin counts. The
ash/spotlight output is triggered via either the SemWire
interface or a dedicated pin.
In sleep mode, the device reduces quiescent current to
100μA while continuing to monitor the serial interface.
The two LDOs can be enabled when the device is in sleep
mode. Total current reduces to 0.1
μA in shutdown.
SC621
VIN
SWIF
FLEN
BYP
AGND
PGND
VOUT
BL1
FL
FLASH
C
IN
2.2μF
MAIN BACKLIGHT
LDO1
GREF
C1+
SemWire
Interface
Flash
Control
V
LDO1
= 2.5V to 3.3V
V
LDO2
= 1.5V to 1.8V
V
BAT
C
BYP
22nF
C
OUT
4.7μF
C
LDO2
1μF
C
LDO1
1μF
C2
2.2
F
C1
2.2μF
LDO2
BL2
BL3
BL4
C2+C1- C2-
US Patents: 6,504,422; 6,794,926
Typical Application Circuit
October 20, 2009
