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BQ27Z561-R2: Route BAT_SNS through NU

Michael Balourdas
Expert 5365 points
Part Number: BQ27Z561-R2

Hello,

Can the BAT_SNS pin be routed through the NU pin to avoid using a microvia?

Thanks,

Michael

  • 0
    TI__Mastermind 25981 points

    Hello Michael,

    Does the NU pin have continuity with the BAT_SNS? If it does, then it might be ok to route it through the NU.

    Regards,
    Jose Couso

  • 0 in reply to Jose Couso
    TI__Expert 5365 points

    Hi Jose,

    Would you be able to confirm whether or not it is ok? Customer needs a firm answer.

    Thanks,

    Michael

  • 0 in reply to Michael Balourdas
    TI__Mastermind 25981 points

    Hi Michael,

    I asked the hardware designer. As soon as he replies, I will get back to you.

    Regards,
    Jose Couso

  • 0 in reply to Jose Couso
    TI__Expert 5365 points

    Hi Jose,

    Any update?

    Thanks,

    Michael

  • 0 in reply to Michael Balourdas
    TI__Mastermind 25981 points

    Hello Michael,

    The hardware engineer did not get back to me.

    I went ahead and checked for continuity in our EVM, and BAT_SNS and NU do not have continuity. They are not connected to each other. I then powered BAT_SNS with 3.62V and checked NU voltage and it was about 0.25V. Hence, NU cannot be used as BAT_SNS.

    Where did the customer find out that this could be done? The only misleading place I could think of is Section 10.2 Layout Example in the datasheet (see below). This is a layout example, not the actual internal hardware of the device. In the red below, it is mentioned that NU has not contact in the bottom layer, this can be confusing leading to customers to think that NU is connected to BAT_SNS in the top layer. This is not the case.



    Regards,
    Jose Couso

  • 0 in reply to Jose Couso
    TI__Expert 5365 points

    Hi Jose,

    Maybe a slight miscommunication here, the customer didn't think they could use NU as the BAT_SNS. The question was rather can they route a trace from the BAT_SNS pin under the NU pin so that they don't have to use a microvia to connect to BAT_SNS. Essentially they want to do what that picture shows, except have that trace be on the top layer.

    Thanks,

    Michael

  • 0 in reply to Michael Balourdas
    TI__Mastermind 25981 points

    Hi Michael,

    Routing on the top layer essentially means that the route of the BAT_SNS will touch the NU pin. This will imply that the BAT voltage will power NU with the same voltage. This could be dangerous if the NU voltage is not a floating voltage. I do not know how the device looks internally. The datasheet does not specifies the voltage rating of the NU pin or what its function is. All we know is that it is a Not Connect pin.  

    I am inclined to say no, but give me a day to follow up with the hardware design team.

    Regards,
    Jose Couso

  • 0 in reply to Jose Couso
    TI__Mastermind 25981 points

    Hello Michael,

    I just received an update from the designer. The designer says that it should not be an issue to route. It seems like the NU is not used in the FW variant of this hardware device. 

    Regards,
    Jose Couso

  • 0 in reply to Jose Couso
    TI__Expert 5365 points

    Great, thank you!