Demonstration Circuit 565 is a constant-frequency synchronous boost converter using the LTC3421. Guaranteed to start-up at 1V input voltage, this converter provides up to 95% efficiency. For 1.8V minimum input voltage, this converter can provide up to 1A load current. This converter has true output disconnect by eliminating body diode conduction of the internal PMOS rectifier. This feature reduces the inrush current during start-up and isolates the load from input source in shutdown to eliminate any leakage current. With the VREF output and low-battery comparator disabled, the IC only draws less than 1mA in shutdown. The output voltage is set at 3.3V. A different output voltage in the range of 2.4V to 5.25V can be obtained by changing one of the feedback resistors. The switching frequency is set at 1MHz, which is a good trade-off between efficiency and size. The frequency can be adjusted by selecting R13 at RT pin. It can also be synchronized to an external clock for noise-sensitive applications. Long wires from input sources (such as wall adaptors) can cause large voltage spikes during initial plug-in. C12 is installed on DC565 to damp the possible voltage spikes. C12 is not required for applications where input source is close to the regulator. Please refer to Application Note 88 for details. For VOUT > 4.3V applications, D1, Q1, R18 and C10 have to be installed to limit the peak switch voltage below the absolute maximum rating. Instead of using a schottky diode connected directly from SW pin to the output, this active snubber keeps the LTC3421 true output disconnect feature. R18 can be used to limit the current going through Q1 in short-circuit conditions. The optional circuit at ILIM pin can be added to provide current limit foldback for extended short-circuit conditions. Refer to Short Circuit section in the datasheet for details.