Demonstration Circuit DC425 is a constant-frequency synchronous Buck-Boost converter using the LTC3440. The input range is from 2.5V to 5.5V, making it ideal for single-cell lith-ium-ion or three-cell NiCd/NiMH battery applications. This converter provides up to 95% efficiency, much higher than traditional Buck-Boost converters. For 2.5V minimum input voltage, this converter can provide up to 500mA load current. The output voltage is set at 3.3V. A different output voltage in the range of 2.5V to 5.5V can be obtained by changing one of the feedback resis-tors. The frequency is set at 1MHz, which is a good trade-off between efficiency and size. The frequency can be modified by changing R6 or by synchronizing to an external clock. In shutdown, the board draws about 2.5µA, where 2µA goes through the 1M? pull up resistor (R4) and the IC it-self draws less than 1µA.