LM3551_06 Datasheet, PDF (1/15 Pages) National Semiconductor (TI) – 1A White LED Driver with Flash Timeout Protection

February 2006
LM3551/LM3552
1A White LED Driver with Flash Timeout Protection
General Description
The LM3551 and LM3552 are fixed frequency, current mode
step-up DC/DC converters with two integrated NFETs that
can be used for precision LED brightness control. The de-
vices are capable of driving loads up to 1A from a single-cell
Li-Ion battery.
The LM3551 and LM3552 can drive one or more high current
flash LEDs either in a high power Flash mode or a lower
power Torch mode using the TORCH/FLASH pin. A program-
mable Timeout function on the FTO pin forces the internal
NFETs to turn off after a certain user defined time. An
external SD pin (LM3551) or EN pin (LM3552) is available to
put the device into low power shutdown mode. During shut-
down, the feedback resistors and the load are disconnected
from the input to avoid leakage current paths to ground.
User programmable soft-start circuitry has been integrated
to eliminate large inrush currents at start-up. Over-voltage
protection circuitry and a 1.25MHz switching frequency allow
for the use of small, low-cost output capacitors with lower
voltage ratings.
The LM3551 and LM3552 are available in a low profile 14 pin
LLP package.
Features
n Up to 1A total drive current
n Flash timeout protection
n Independent Torch/Flash/Shutdown modes
n LED disconnect in shutdown
n Programmable soft-start limits inrush current
n Over-voltage protection
n Wide voltage range 2.7 to 5.5V
n 1.25MHz constant switching frequency
n Small, low profile package, non-pullback LLP14 (4mm x
4mm)
Applications
n White LED Camera Flash
n White LED Torch (Flashlight)
n DSC (Digital Still Camera) Flash
n Cellular Camera Phone Flash
n PDA Camera Flash
n Camcorder Torch (Flashlight) lamp
Typical Application Circuits
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