In the application environment of brushless motor with 24-60V, the drive power supply usually uses BUCK circuit to step down to 10-15V. Since the power supply is usually far away from the drive circuit, the bypass capacitor needs to take on the functions of filtering and power supply at the same time, and its capacitance should be at least 10 times that of the bootstrap capacitor to prevent VCC voltage mutation.

When designing the PCB, the bypass capacitor should be close to the VCC and COM terminals, and the chip capacitor should be connected in parallel with the electrolytic capacitor to reduce the equivalent series resistance (ESR). In addition, the output end of the BUCK circuit needs to be equipped with an additional filter capacitor to ensure stable power supply.

 The power MOSFET circuit has a large current change rate (di/dt), and the parasitic inductance on the line easily causes high-frequency oscillation (as shown in Figure 2). This oscillation not only interferes with the signals of the VS and COM ports, but may also generate positive and negative spike voltages at the VS port (as shown in Figure 3), and in severe cases may even damage the driver chip.

To suppress the interference caused by such parasitic effects, the following measures can be taken:

On the one hand, appropriately increasing the gate drive resistance can reduce the switching speed of the MOSFET, thereby reducing di/dt and alleviating the oscillation problem;

On the other hand, for high-frequency oscillation of the VS port, a 1 - 20Ω resistor can be set at the VS port to suppress it;

For COM ports, it is recommended to adopt a single-point grounding strategy, that is, connect it to the power ground through a short and thick copper foil to avoid ground loop interference.