App note: GPIO Expander Provides Charge Pump for Blue LEDs

Adding blue LEDs to a interface panel looks cool. The down side is that some blue LEDs require more than 3.5V to work, which can be a hassle if your design works on 3.3V.

This app note from Maxim explains how to implement a charge pump on their I2C GPIO expander ICs using the built in pulse-width modulator. With this design you can built a full interface panel with only one IC and a few discrete components, and remotely connect it to a mainboard using only 3 microcontroller pins.