DRV8323R: DRV8323RS Gate Drive Issue

Part Number:DRV8323R

Hello,

Hope you help out here.

For a customer of mine I am forwarding their question about unstable gate drive voltage of the low side FETs with the DRV8323RS:

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We are using the DRV8323RS in a 3 phase BLDC motor drive application with a supply voltage of 30V. Gate drive voltage of the low side FETs seems to be unstable and there are moments that drive voltages become as high as 23.65V where it should be about 12V – 13V max. The power FETs that we use (IRF7480M) have a 20V absolute maximum rating which makes me concerned. The situation seems to be at its worst when all 3 low side FETs need to be switched on at the same time (equal PWM for all channels) and the source current setting (for the low side) is the highest value available.

We can find settings that keep the gate voltages just below 20V but we do not know anything about the spread over several IC’s (and future batches) or dependencies (temperature, supply voltage, …) so we cannot asses how bad it can get. We are considering TVS diodes to protect the gates but we don’t know if this will result in unacceptable internal dissipation or degradation.

The issue was also reported by Konrad Holzmann (DRV8323R: VGLS voltage swing) but the forum does not show a response. We have the same effect but much higher gate voltages. Next screenshot illustrates the relevant signals for one phase only but for the other phases it is the same.

Yellow: Gate drive voltage low side 5V/div

Green: Switch node voltage 5V/div

Pink: output current (10A/div)

First 2 cycles have equal PWM for all phases and no output current

Next 2 cycles PWM is slightly unequal (compared to the other phases) resulting in output current and now correct gate voltage

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