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 leads to the following: question
When the lower tube is turned on, the upper tube should be turned off, and the input terminal of the driver should be low level. Since the input terminal is pulled down is not an ideal 0 resistance value, but has a certain impedance, the negative pressure of VSW has The level of the input signal of the upper driver may be pulled high, and the logic error of the input signal may cause the upper driver to mistakenly trigger the output high level, and the upper and lower tubes will be short-circuited.
The voltage overshoot of the bootstrap capacitor CB. Under extreme conditions, the excessive voltage will cause damage to DH1, which is determined by the maximum power of the DH1 protection diode inside the IC. In some designs, in order to improve the power of ESD protection, the SCR thyristor structure will be used. Under a large operating current, a latch-up effect will occur, causing the system to not work properly.