DRV8353: Problem with gate charge / discharge

Part Number: DRV8353
Other Parts Discussed in Thread: TMS320F28069,

Hello,

I am working with a motor control custom board that includes a DRV8353 driver and a TMS320F28069 microcontroller. We are using instaspin library to control the PMSM motor.

The board normally works ok, but sometimes the drive break specially when high Idrive values in the driver configuration are used. We have plot the voltage at the mosfet gates and we have seen something quite strange. The following picture shows the voltage at GHA pin (yellow) and GLA pin (blue). As you can seen the  voltage at GHA pin starts to decline from 34V (please, notice that signal are refered to GND), but it doesn't fall to 0V. When the Low side mosfet is triggered, the higw side gate volltage fall to 0V, but an oscillanting transitory signal is seen (negative voltage are also observed)

Figure 1: 

We have also seen that this transitions do not present the same pattern always. The following figure shows the same measurement, but in this case the voltage at GHA seems to be correctly performed

Figure 2

Figure 1 happens when DRV switches off the High side mosfet while one of the other high side mosfet is switched on.

Figure 2 happens when DRV switches off the high side mosfet and no other high side mosfet is switched on

We have tested with various Idrive configurations. With low Idrive values the spikes nearly dissapears, but the GHA voltage is not always drive to 0 before the low side is switched on (as in the first image). 

Do you have any advice?

Thank you in advance

  • Hi Borja, and thanks for your question!

    Our experts will get back to you tomorrow!

    Thanks,

    Matt

  • Hi Borja,

    Please note that it is OK to reference GLx to GND, however GHx should be referenced to SHx. This is because if you reference the high side gate to ground, you will be measuring the voltage drop at SHx + the High side gate.

    Reading the waveform left to right, we see that the high side MOSFET is turned on and is sitting at about 34V. Once the high side MOSFET is turned off, the voltage on the gate doesn’t drop to zero. Instead the voltage drops down to SHx, which is about 24V. This is because the current through an inductor can’t change instantaneously. Once the high side MOSFET is turned off, current flows from SHx up though the high-side MOSFET body diode into the supply. Once the low side MOSFET turns ON, then the current will stop flowing up through the high side body diode and start flowing through the low-side MOSFET. Now SHx is pulled to ground.

    Also, please see the link below, it covers selecting the best IDRIVE setting and why this is essential:

    https://e2e.ti.com/support/motor-drivers/f/motor-drivers-forum/796378/faq-selecting-the-best-idrive-setting-and-why-this-is-essential

    I hope you found this helpful.

    Thanks

    Michael