Tool/software:
Hi Sir ：
During the continuity test of power on and off, there was an IC burning phenomenon; Tests have found that the chip may have been burned out due to excessive directional electromotive force, with a maximum voltage of 68V measured. The attached schematic is provided, PCB ， There are also test waveforms, etc; Please help suggest how to modify it to suppress reverse electromotive force and prevent chip burnout. Thank you ！
Hi Anson,
Thanks for reaching out to us.
While driving a motor it is impossible to eliminate back EMF, BEMF voltage while the motor is spinning. Proper circuit design would help mitigate the voltage pumping on the VM pin caused by BEMF.
I see the following issues in the schematic.
1) Series diode for reverse battery protection. This diode prevents the BEMF from getting dissipated by the power supply source.
2) Insufficient bulk capacitor value C220 in the system - only 4.7 μF. Because of the series diode and small bulk capacitance the voltage at this node can get very high, like 68 V that was measured and damage components and driver IC. Please request the customer to increase the bulk capacitance to > 100 μF for example, 220 μF and check if high voltage pumping issue is mitigated. If it still does not then series diode D9 must be removed and replaced by a 0 Ω resistor. If customer wants reverse battery protection they should a power FET based protection similar to what we have in the DRV8889-Q1EVM. Regardless the bulk capacitor closest to the VM pin must be sufficient to mitigate voltage pumping especially if the harness to the power supply carries some inductance. See this application note, https://www.ti.com/lit/an/slvaft0/slvaft0.pdf. It applies to stepper motor drives as well.
Regards, Murugavel
