SLUSFS4A September 2025 – September 2025 UCC27734-Q1 , UCC27735-Q1
PRODUCTION DATA
The optional resistor RBOOT is selected to limit the current in DBOOT and limit the ramp up slew rate of voltage of VHB–HS. For this design, we selected a current limiting resistor of 2.2Ω. The bootstrap diode current (IBOOT(pk)) was limited to roughly 6.5A.
The power dissipation capability of the bootstrap resistor is important. The bootstrap resistor must be able to withstand the short period of high power dissipation during the initial charging sequence of the bootstrap capacitor. This energy is equivalent to 1/2 × CBOOT × V2. This energy is dissipated during the charging time of the bootstrap capacitor (~3 × RBOOT × CBOOT). Special attention must be paid to use a larger size RBOOT when a larger value of CBOOT is chosen.