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DRV8303: Ground Isolation with Host MCU

Eclipze
Intellectual 641 points
Part Number: DRV8303
Other Parts Discussed in Thread: MSP430F5329,

I am looking to isolate the ground between the DRV8303 and the host MCU, to prevent motor ground current passing through the MCU.  I had tried to provide some isolation with the AGND, however this resulted in SPI configuration data from being lost.  The host MSP430F5329 is locking up from conducted emissions, to the point the watchdog fails to invoke a reset.  

Pictured below is the layout.  Unfortunately the MCU sits in between the input power connection and the motor outputs.  I am not able to change this topology or the current path to the motor.  As an interim measure, I have added a 10R resistor between the MCU to DRV grounds.

Digital isolators may help, such as the ISO7141.  Would struggle to find the space.  Although supplying the REF voltage and having a stable ground reference for the SO1, SO2 current feedback is still needed.

If any one has some suggestions, they would be very much appreciated!

  • 0
    Prodigy 150 points
    Hello,
    I think that in your application the problem is related to DRV8303 and its ceramic capacitors.
    DRV series needs careful layout. Be sure that you place 100n seramic capacitors very close to GVDD, DVDD, AVDD and PVDD pins of DRV8303.
    Place a solid ground plane under the driver IC.
    You may check the following application note:
    www.ti.com/.../slva552.pdf

    Isolation for this applicaiton is not easy. But unless your currents are extremly high you may solve this problem with carefull placement .
  • 0 in reply to Murat_
    TI__Expert 4650 points
    Hi Eclipze,

    I would agree with Murat above, this is most likely an issue of both bypass capacitance around our device as well as significant ground bounce on the ground plane as the power FETs are switching.

    I would recommend either adding more local ceramic bypass capacitance to the DRV8303 and Power MOSFET Drain -> ground, or trying to better isolate the ground return path of the power MOSFETs to the power supply so that the return path does not pass under the MCU.
  • 0 in reply to Phil Beard
    Intellectual 641 points
    Thanks both. I would like to ensure the motor current for the ground path follows the intended part to minimise EMC and possible ground bounce with the MCU. What I am unsure about, is how to provide that isolation. If I could interface to the DRV8303 using a signal ground to AGND, but have the power stage reference to the PGND, that would be great. However this didn't work as I'd hoped.

    Can you suggest how I can isolate the ground return, such that motor current follows the intended path?
  • 0 in reply to Eclipze
    TI__Expert 4650 points
    Hi Eclipze,

    For PCB EMC / EMI layout recommendations, we have the following application note:

    www.ti.com/.../szza009.pdf

    For specifics related to half-bridge power MOSFET layout characteristics, we have an app note written by our Buck-Converter team. Many of the suggestions they make in the app note are directly related to best-practices for half-bridge layout using our gate driver devices.

    www.ti.com/.../slyt682.pdf