The UCC27288 does not incorporate the bootstrap diode necessary to generate the high-side bias for HO to work satisfactorily. The characteristics of this diode are important to achieve efficient, reliable operation. The characteristics to consider are reverse voltage handling capability, repetitive peak forward current, forward voltage drop, forward and reverse recovery time, and dynamic resistance. As the UCC27288 is 100V rated gate driver, the external bootstrap diode must be at least 100V rated. Peak forward current rating depends on multiple system parameters such as high-side and low-side duty cycle, value of bootstrap capacitor, value of series resistor, and allowed voltage ripple on the bootstrap capacitor. Generally, low forward voltage drop diodes are preferred for low power loss during charging of the bootstrap capacitor. Schottky diodes have low forward voltage drop and can be used with the UCC27288. The dynamic characteristics to consider are diode recovery time and stored charge. Diode that has less than 50ns of forward and reverse recovery times is suitable in most applications.

Specifically in very high switching frequency applications, for example in excess of 1 MHz, and where the low-side minimum pulse widths are very small, the diode peak forward current could be very high and peak reverse current could also be very high, specifically if high bootstrap capacitor value has been chosen. In such applications it might be advisable to use Schottkey diode as bootstrap diode and provision of external series resistor. MURS210 diode with 1 Ohm series resistor will work with the application example described here.