1 Introduction

For common nonsynchronous boost converters, the load (Vout) is connected to the input port through the high-side diode and the inductor when output voltage drops below the input, causing a big current spike through the device. Figure 1-1 depicts the device behavior when Vout drops below Vin.

Obviously, the network of Figure 1-1 does not allow control over inductor current. For the start-up process, the moment Vin is connected, the diode becomes forward biased, and there is a big inrush current into the output capacitor. For output short situations, Vin is shorted to GND through the leakage path, causing damage over the whole system.

To suppress this inrush current and achieve smooth current control under a Vin > Vout condition, TI applies multiple control strategies and topologies to limit the inductor current under start-up or output short conditions. This application note introduces behaviors of TI synchronous boost, which, with the application of switchable body diode or extra Isolated Field-Effect Transistor (ISO FET), is capable of controlling current when Vin > Vout during start-up and output short situation.