The LM2755 is a charge-pump-based, constant current LED driver capable of driving 3 LEDs
with a total output current up to 90mA. 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-compatible 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 soft-start circuitry eliminates high inrush current at start-up. The
LM2755 consumes 3µA (typ.) of supply current in shut-down.
The LM2755 is available in Texas Instruments' tiny 18-bump thin DSBGA package.
