• Grounded Cathode LED Operation for Improved Thermal Management
• 1.5-A High-Side Current Source for Single LED
• Accurate and Programmable LED Current from 46.9 mA to 1.5 A
• > 85% Efficiency in Torch Mode (at 100 mA) and Flash Mode (at 1 A to 1.5 A)
• Small Solution Size: < 20 mm2
• LED Thermal Sensing and Current Scale-Back
• Soft-Start Operation for Battery Protection
• Hardware Enable Pin
• Hardware Torch Enable
• Hardware Strobe Enable
• Synchronization Input for RF Power Amplifier Pulse Events
• VIN Flash Monitor Optimization
• 400-kHz I2C-Compatible Interface
• I2C-Compatible Programmable NTC Trip Point
• 0.4-mm Pitch, 16-Pin DSBGA Package

Camera Phone LED Flash

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 mA to 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.