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DRV8308: Varying Torque causing overshoot

Justin Leach
Prodigy 10 points
Part Number: DRV8308
Other Parts Discussed in Thread: MCF8329A

Hi All,

Please find attached a mapping of all registers. My setup consists of the DRV8308 device driving a 450W motor at ~4000RPM on a battery driven system with nominal voltage of 25.6V in the Clock Frequency Mode. The issue that I face is that this motor will be under varying loading on the output ranging from no load to a full 450W load as well as varying battery voltage between 22V and 28V. If I tune the system for less load I am unable to drive the motor under full load but if I tune for full load then the motor overshoots way too much under no load. I add that the current sense has been adjusted to allow this much power.

I have tried setting what I believe is the integral term (SPDGAIN) but it seems that the total gain of the system (LOOPGAIN + FILK and COMPK) has much more of an effect on the available output torque.

In the case where the system has too much load and then unlocks the lockn pin it seems that the rpm and duty cycle per phase immidiatly drops quite a bit. I would expect that the integral should then push the duty cycle to 100% but this never seems to be the case and I'm curious as to why or how I may be able to achieve this?

I patiently await suggestions and some help with my understanding, thanks,

Justin

  • 0
    TI__Genius 12215 points

    Hi Justin,

    The device tends to be tricky to tune and due to its age support for tuning this device will be limited. We generally recommend moving from the DRV8x devices that offer integrated control over to our MCx product line. Based on your motors power requirement I would recommend taking a look at the MCF8329A device.

    For this device and based on what you have accomplished so far, I would recommend trying to increase SPDREVS to see if this helps the performance of the motor.

    Regards,

    Joshua