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DRV7308: Slew rate setting - falling slew rate

Jade Han
Intellectual 1685 points
Part Number: DRV7308

Tool/software:

Hello team,

I had a quick question about slew rate control & setting.

Currently my customer is reviewing with our DRV7308, with built PCB.

They have the slew rate set to 10V/ns, and when they measured the slew rate, rising slew rate is 10V/ns, but it seems falling slew rate is slower, at around 5V/ns.

Is the slew rate settings supposed to only be applied to rising slew? Is falling slew rate supposed to be 5V/ns?

(+) The IC's top marking was as below, so I think the IC they are using is the latest 2.0 version sample.)

Thank you.

Best regards,
Jade

  • 0
    TI__Mastermind 26756 points

    Hi Jade, 

    Thank you for your question! 

    What you are seeing on the turnoff of the GaN is actually the discharge time of the Coss + PCB capacitance based on the motor current. The FET itself is actually off, but the OUTx voltage remains high for longer as the output capacitance discharges (for current flowing out of the phase turning off the high side) You will find that the slew rate of OUTx on the turnoff is dependent on the motor current, since this current is the rate at which the output capacitance is being discharged. This happens during the hi-z period when both FETs are off so this slew is not actually the slew rate of the GaN FET itself since the FET is already off. Let me know if you have any questions!

    Regards,

    Anthony Lodi