Half-bridge gate driver with integrated bootstrap diode
The Infineon IR21531SPBF is a high-voltage half-bridge gate driver designed for driving N-channel MOSFETs in a synchronous half-bridge configuration. It integrates a bootstrap diode for the high-side supply, simplifying the external component count in offline AC-DC converters, ballasts, and motor-drive inverter stages. The driver operates from a 10 V to 15.6 V supply rail, which covers the standard 12 V and 15 V bias rails common in power electronics. The 600 V high-side bootstrap rating allows the high-side driver to float with the switching node in line-voltage applications up to 400 VDC bus. Rise and fall times are 80 ns and 45 ns typical respectively, giving enough margin to set a dead-time that avoids cross-conduction in the half-bridge at switching frequencies up to several hundred kilohertz. The RC input circuit sets the oscillator frequency with an external resistor and capacitor, a common topology in self-oscillating half-bridge controllers.
The 600 V high-side voltage rating (bootstrap) is the maximum voltage the high-side driver can withstand when the half-bridge switching node rises to the DC bus. In a typical 230 VAC input offline converter, the rectified DC bus is around 310 V to 400 V, so the 600 V rating provides a comfortable margin for transients and ringing. The bootstrap diode is integrated, which saves one external diode and one resistor compared to discrete bootstrap implementations. The supply voltage range of 10 V to 15.6 V means the undervoltage lockout thresholds are set for standard gate-drive bias rails. A 12 V rail is the most common — it keeps gate drive voltage within the typical Vgs rating of standard N-channel MOSFETs while staying above the driver's UVLO rising threshold.