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DRV8332 Isolation between Power and Signal Circuit

Pantelis
Prodigy 150 points
Other Parts Discussed in Thread: DRV8332, DRV8301, DRV8312

Hello Everyone!

I am designing a PCB for a 3-phase inverter and I am planning on using the DRV8332!

What I would like to ask is, if you think I should isolate the microcontroller from the Inverter. I mean in general it is often preferable to have some isolation between the Microcontroller and the drivers, however I haven't seen anything like that either here at the forum or to the datasheet of the DRV8332.

Maybe I am missing something obvious, so if that's the case excuse me :)

Thank you in advance for your answers!

Regards,

  • 0
    TI__Guru** 114905 points

    Hi Pantelis,

    Using isolation is application dependent. In general, it depends on the amount of noise in the system.

    For an example of a system with micro, gate drivers and FETs, please see the LINK . Together the DRV8301 gate driver and FETs are similar to the DRV8332 though it can handle much higher current.

  • 0 in reply to Rick Duncan
    Prodigy 150 points
    Hello Mr Duncan,

    Thank you very much for your answer and for the schematic. The reason I asked was because I amthinking whether I should put optocouplers between the Microcontroller and the DRV8332 pulse input pins, so as to isolate the power circuit with the signal circuit or not.

    Also by saying depends on the amount of noise, you refer to the amount of noise of the power system, so that it won't affect the digital ground and the various analog measurements? Or is it something else?

    Excuse me for that, is just that I 'm not sure, if I should avoid having common ground also for circuit protection reasons.

    Regards,
    Pantelis
  • 0 in reply to Pantelis
    TI__Guru** 114905 points

    Hi Pantelis,

    Yes, I am referring to the amount of noise (ground bounce) of the power system. If the ground bounce is too high, a logic high the digital side can be interpreted as a logic low. If the ground bounce is too low (below ground), diode paths can be turned on.

    Adding isolation adds costs, and may or may not be required. That is why I said it is application dependent.

    If this is a prototype, you could consider adding the optocouplers plus the ability to route signals through the optocoupler or around. This would provide the ability to evaluate both.

     

  • 0 in reply to Rick Duncan
    Prodigy 150 points

    Dear Mr Duncan,

    Once again thank you very much for your response!

    It is a prototype, however I don't know how it would be possible to put both solutions on the same board. I think the complexity would increase significantly, since that would mean that I would also need to have separate sources for the "before" and "after" isolation parts, and also have the ability to either connect or disconnect the grounds of these sources, depending or whether I am going to use the isolation or not.

    Definitely is not something inevitable, but I could give it a try.


    Actually, now that I am thinking about, since I would like to connect some pins of the inverter with my microcontroller (Reset, Fault, OTW), eventually they will need to have common ground, because also isolating these pins would be too much... So I guess there is no other solution than keeping a common ground and not using any isolation. What would you think about that?

    Thank you for your time and for your answers.

    Regards,
    Pantelis

  • 0 in reply to Pantelis
    TI__Guru** 114905 points

    Hi Pantelis,

    As you mentioned, it would be difficult to create a board that handles both.

    In general, there is no need for isolation.  In the schematic attached, the system can handle 40A.

    I forget to mention that other EVMs contains the DRV8312 (very similar to the DRV8332) DRV8332EVM_LINK and the DRV8432 (one half bridge more than the DRV8332) DRV8432EVM_LINK . These two links can also be used for reference.

  • 0 in reply to Rick Duncan
    Prodigy 150 points
    Dear Mr Duncan,

    Thank you for all your help and excuse me for the delayed response.

    I will have a look at the given datasheets and start designing the PCB. I will come back some days later to give you some feedback!

    Moreover I should have some good study on Ground immunity, even though I do not think it would be such a problem when using such an integrated solution as DRV8332.

    Thank you for everything.

    Regards,
    Pantelis