• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 667 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ25792: ACFETx , RBFETx

AJ
Intellectual 570 points
Part Number: BQ25792

Hi Support Team,

I am looking at the BQ25792 datasheet, and wanted to confirm the orientation of ACFETx/RBFETx 

I believe RBFETx should be placed before ACFETx to protect VACx pins against reverse polarity on VINx
As per absolute maximum rating, VACx min is -2V. 

Can you please confirm if ACFETx / RBFETx can be swapped? Or the application must ensure positive polarity at VINx?

Best,
AJ

  • 0
    TI__Guru**** 166626 points

    Alex,

    Unfortunately, simply swapping the FETs will not implement reverse input protection.  You will need to add an additional FET as shown below.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 570 points

    Hi Jeff,
    Thank you for confirming. though, it's not clear how the proposed solution works. Is it possible to show connection to VACx pins and VBUS?

    Also, can you please elaborate why swapping Drain and Source is not possible. 

    reverse polarity case,

    • body diode is reversed biased and it blocks and protects the VACx pins

    positive polarity case,

    • body diode is forward biased and VACx pins see VIN - VF_body_diode. 
    • ACDRVx drive N-Ch gate and FETs turn-ON VACx pins see ~VIN 


    If understand the datasheet correctly, the VACx are used as voltage sense pins. Is it possible to add a small signal diode as follow ?



    Best,
    AJ



  • 0 in reply to AJ
    TI__Guru**** 166626 points

    Hi Alex,

    VBUS connects to the drain of Q3 and VAC connects to the drain of Q1.  You are correct that a diode in series with VAC would be required even with the additional Q1 circuit.

    Regards,

    Jeff