In conventional non-synchronous boost converters, the load (Vout) is connected to the input voltage through the rectifier diode when the device is shutdown (EN = low).

Figure 1-1 Conventional Non-synchronous Boost Converter

In some always-on systems, the output load must be connected to the input voltage when the boost converter is disabled. In Figure 1-1, the load is connected to the input voltage through the inductor and rectifier diode resulting in a large voltage drop and power loss. In synchronous boost converters, a HS-FET is used to replace the rectifier diode. To improve device performance, load connection strategies like pass-through and bypass are proposed for such demands.

When the load is not powered by the device during shutdown and the system is sensitive to shutdown power loss, the device needs to realize true shutdown. In this case, load disconnection function is important. The function also allows the output short protection and minimizes the inrush current at start-up.

This application note introduces typical boost behaviors of load connected or disconnected to the input voltage during shutdown.