LM2755 Datasheet | National Semiconductor

LM2755 Charge Pump LED Controller with I2C patible Interface October 2007 LM2755 Charge Pump LED Controller with I2C patible Interface .. in Micro SMD General Description The LM2755 is a charge-pump-based, constant current LED driver capable of driving 3 LEDs with a total output current up to 90m A. The diode current waveforms of each LED can be trapezoidal with timing and level parameters (rise time, fall time, high level, low level, delay, high time, low time) programmed via an I2C patible interface. The 32 brightness levels found on the LM2755 are exponentially spaced (as opposed to linearly spaced) to better match the response of the human eye to changing brightness levels. The device requires only four small and low-cost ceramic capacitors. The LM2755 provides excellent efficiency without the use of an inductor by operating the charge pump in a gain of 3/2 or in a gain of 1. Maximum efficiency is achieved over the input voltage range by actively selecting the proper gain based on the LED forward voltage requirements. The pre-regulation scheme used by the LM2755 is optimized to ensure low conducted noise on the input. An internal softstart circuitry eliminates high inrush current at start-up. The LM2755 consumes 3µA (typ.) of supply current in shut-down. The LM2755 is available in National’s tiny 18-bump thin micro SMD package. Features - - - - - - - - - - - 90% Peak Efficiency Total solution size < 13mm2 No Inductor Required: Only 4 Inexpensive Ceramic Caps 3 Independently Controlled Constant Current Outputs Programmable Trapezoidal Dimming Waveform on Each Output Programmable Timing Control Via Internal Registers and External Clock Synchronization Input 32 Exponential Dimming Steps with 800:1 Dimming Ratio Programmable brightness control via I2C patible interface Hardware Enable Pin Wide input voltage range: 2.7V to 5.5V Tiny 18-bump thin micro SMD: 1.8mm x 1.6mm x 0.6mm Applications - - - - Indicator LEDs Keypad LED Backlight...