The LM3556 is a 4-MHz fixed-frequency synchronous boost converter plus 1.5-A constant
current driver for a high-current white LED. The high-side current source allows for grounded
cathode LED operation providing flash current up to 1.5 A. An adaptive regulation method ensures
the current source remains in regulation and maximizes efficiency.
The LM3556 is controlled via an I2C-compatible interface.
Features include: a hardware flash enable (STROBE) allowing a logic input to trigger 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, and an integrated comparator designed to monitor
an NTC thermistor and provide an interrupt to the LED current. With a fast 1-μs transition from 0
46.9 mA, the TORCH input pin can be used to develop custom LED current waveforms.
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 operates
over a −40°C to +85°C temperature range.
For all available packages, see the orderable addendum at
the end of the data sheet.
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