The LM3646 utilizes a 4-MHz fixed-frequency synchronous boost converter to provide power
to dual 1.5-A constant current LED sources. The high-side current sources allow for grounded
cathode LED operation providing flash current up to 1.5 A total. An adaptive headroom regulation
scheme ensures the LED currents remain in regulation and maximizes efficiency. The combination of
dual LED driving capability, high LED current, small solution size and high level of adjustability
make the LM3646 perfect for camera phone LED flash and torch applications.
The LM3646 is controlled through an I2C-compatible interface.
The main features of the LM3646 include: a hardware flash enable (STROBE) input for direct
triggering of the flash pulse, a hardware Torch enable (TORCH) for movie mode or flashlight
functions, a TX input which forces the flash pulse into a low-current torch mode allowing for
synchronization to RF power amplifier events or other high-current conditions, an integrated
comparator designed to monitor an NTC thermistor and provide an interrupt to the LED current, and a
programmable input voltage monitor which monitors the battery voltage and can reduce the flash
current during low battery conditions. A hardware enable (ENABLE) input provides a hardware
shutdown during system software failures.
The 4-MHz switching frequency, overvoltage protection, and adjustable current limit allow
for the use of tiny, low-profile inductors and (10-µF) ceramic capacitors. The device is available
in a small 20-bump DSBGA package and operates over the –40°C to 85°C temperature range.
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