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DRV8703-Q1: GND and signal connection between u-com and DRV8703

user6321073
Prodigy 70 points
Part Number: DRV8703-Q1

Dear TI team,

I have the questions about GND and signal connection between u-com and DRV8703.

This question is related to the thread of "DRV8703-Q1: GND connection" and "DRV8703-Q1: If the battery is coonected in reverse", we asked to our agent and they asked on this forum, so I asked again with more detailed information instead of him.

Please refer to the attached pdf file, and please reply to me.

Best Regards,

Matsunaga

DRV8703confirmation_20200414.pdf

  • 0
    TI__Guru 56650 points

    Matsunaga,

    <Question 1>

    By this connection, can DRV8703 operate correctly according to the u-com control?

    Answer: DRV8703 circuitry ground and u-com circuitry ground joint is put externally. So, I cannot say that board will operate correctly because it depends on the external circuit.

    1. The joint connection is related to external battery circuit connection.

    2. All the u-com control signal voltages for the DRV8703 circuit are reference to the external ground. The signal noise level is also depended on the external ground.

    I would recommend putting the DRV8703 ground and u-com circuit ground joint inside the PCB.

    <Question 2>

    Considering about the reverse connection of "+" and "-" wire of the battery to the PCB as below picture,

    is DRV8703 protected (not damaged or broken)?

    *This reverse connection means that VM connect to "-", and GND (device ground) connect to "+".

    Answer: DRV8703 circuit and u-com circuit are in parallel. DRV8703 reverse battery protection circuit can support DRV8703 circuit. But, not u-com circuit. Customers have to put DRV8703 reverse battery protection circuit in front of both DRV8703 circuit and u-com circuit to protect both circuits.

  • 0 in reply to Wang5577
    Prodigy 70 points

    Dear Wang san,

    Thank you for your reply. 

    As for Question 1,

    Then, if GND of u-com and DRV8703 in PCB is same voltage (0V) , and if the noise level of u-com and DRV8703 in PCB is same, can DRV8703 operate correctly?

    As for Question 2,

    Does your "DRV8703 reverse battery protection" mean "7.3.14.8 Reverse Supply Protection" on the specification sheet?

    Best Regards,

    Matsunaga

  • 0 in reply to user6321073
    TI__Guru 56650 points

    Matsunaga,

    1. I can only say: putting two ground joint in the PCB could eliminate the external connection and noise concern. DRV8703 work or not work is still related to his design and layout. For example: if they still keep DRV8703 circuit and u-com circuit in parallel, the battery reverse protection circuit cannot protect u-com circuit.

    2. Yes. The "DRV8703 reverse battery protection" means "7.3.14.8 Reverse Supply Protection" on the specification sheet.

  • 0 in reply to Wang5577
    Prodigy 70 points

    Dear Wang san,

    Thank you for your reply.

    Then, I have the further confirmation.

    If we use one ground for DRV8703 and u-com in PCB as your recommendation, are both DRV8703 and u-com protected on the reverse battery protection?

    Because, we checked the battery reverse connection in our lab on our "Question 2" condition*, both DRV8703 and u-com is damaged with smoke.

    *"Question 2 condition" means; GND for u-com and GND for DRV8703 is saparated in PCB but the connected at battery terminal, and battery reverse connection only for DRV8703 battery.

    Best Regards,

    Matsunaga

  • 0 in reply to user6321073
    TI__Guru 56650 points

    Matsunaga,

    "we use one ground for DRV8703 and u-com in PCB as your recommendation"

    That doesn't change the DRV8703 circuit and u-com circuit in parallel to connect the input source battery. So, u-com circuit should get damage. The u-com's input source "+" terminal has to been connected to the red circle trace net to get protection from DRV8703 protection circuit.

    If the DRV8703 circuit gets damage, that indicates your reverse protection circuit cannot protect the circuit at a battery reverse condition. Please make sure it works first.

  • 0 in reply to user6321073
    TI__Guru 56650 points

    Matsunaga,

    "we use one ground for DRV8703 and u-com in PCB as your recommendation"

    That doesn't change the DRV8703 circuit and u-com circuit in parallel to connect the input source battery. So, u-com circuit should get damage. The u-com's input source "+" terminal has to been connected to the red circle trace net to get protection from DRV8703 protection circuit.

    If the DRV8703 circuit gets damage, that indicates your reverse protection circuit cannot protect the circuit at a battery reverse condition. Please make sure it works first.

  • 0 in reply to Wang5577
    Prodigy 70 points

    Dear Wang san,

    Thank you for your reply.

    Then, we check our circuit as your information and re-test again.

    Best Regards,

    Matsunaga