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 National’s tiny 18-bump thin micro SMD package.
The LM2755 is a micro‑SMD charge‑pump LED controller that drives up to three LEDs with a total output current of 90 mA. It provides 32 exponentially spaced brightness levels and can operate with either a 1× or 3⁄2× gain to maximize efficiency across a 2.7 V‑5.5 V input range.
The device requires only four low‑cost ceramic capacitors and includes a hardware enable pin, an external‑clock SYNC pin, and an I²C‑compatible serial interface (SCL, SDIO, VIO). Typical applications are indicator LEDs, keypad backlights, display backlights, and fun‑light LEDs.
| Maximum total output current | 90 mA |
|---|---|
| Input voltage range | 2.7 V – 5.5 V |
| Number of LED driver channels | 3 |
| Brightness steps | 32 exponential steps (800:1 dimming ratio) |
| Peak efficiency | 90 % (typ.) |
| Package dimensions | 1.8 mm × 1.6 mm × 0.6 mm |
| External components required | Four ceramic capacitors (e.g., 0.47 µF and 1 µF) |
| Quiescent supply current (shutdown) | 3 µA (typ.) |
| Gain modes | 1× and 3⁄2× |
| Maximum external sync frequency | 1 MHz |
The LM2755 can supply up to 90 mA total, which can be divided among the three LED channels (30 mA each).
It provides 32 exponentially spaced dimming steps, giving an 800:1 dimming ratio.
Only four small ceramic capacitors are required, typically values of 0.47 µF and 1 µF.
The device operates from 2.7 V up to 5.5 V.