The LTC3425, a high-efficiency synchronous boost converter, incorporates a four-phase switching topology to minimize size and deliver ultra-low output ripple. Operating at up to 8 MHz, the converter's internal switches provide a 5-A current limit and can deliver output voltages as high as 5.25 V from input voltages of 0.5 V to 4.5 V. The device provides up to 3 A of continuous output current. In the 32-pin QFN package, they're priced at $4.38 each in quantities of 1000.
Linear Technology Corp.www.linear.com