1 Features
1• Drives Parallel High-Voltage LED Strings for
Display or Keypad Lighting
• Boost Converter up to 90% Efficiency
• Four User-Selectable Full-Scale Current Settings
(20.2 mA, 18.6 mA, 17.0 mA, 15.4 mA)
• Quick-Dimming Enable Terminal (ILOW)
• Simple PWM Duty Cycle Control
• 24-V Overvoltage Protection Threshold
• Fixed 1-MHz Switching Frequency
• Integrated 1-A/40-V MOSFET
• Three Current Sink Terminals
• Adaptive Boost Output to LED Voltages
• Thermal Shutdown Protection
• 29-mm2 Total Solution Size

2 Applications
• Power Source for Smart Phone Illumination
• Display or Keypad Illumination

3 Description
The LM3699 is a three-string, high-efficiency, PWM-
controlled power source for display backlight or
keypad LEDs in smartphone handsets. The high-
voltage inductive boost converter with integrated 1-A,
40-V MOSFET provides the power for three series
LED strings. The boost output automatically adjusts
to LED forward voltage to minimize headroom voltage
and effectively improve LED efficiency.
The ILOW terminal provides a method to quickly
reduce LED brightness during camera flash
operation.
The LM3699 has integrated overvoltage, overcurrent,
and thermal protection.
The device operates over a 2.7-V to 5.5-V input
voltage range and a −40°C to 85°C temperature
range.