1 Features
1• 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

2 Applications
Camera Phone LED Flash

3 Description
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.