Inside the PWM or driver IC, the upper and lower tube drive output terminals have many ESD diodes for protection, as shown in the internal equivalent circuit. Among them, DL1, DL2, DL3 are the VCC of the lower driver and the protection ESD diodes that output Lo, DH1, DH2, DH3 are the VB of the upper driver and the ESD protection diodes that output Ho, and D1 is the highest voltage point VB of the chip bootstrap drive. ESD protection diodes.
If the turn-off speed of the upper tube is too fast, the parasitic inductance of the loop is too large, and the transient negative pressure of the switching node VSW is too large, resulting in an overvoltage of the upper tube and an avalanche, which affects the reliability of the long-term operation of the upper tube, and also causes other question。