• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 40 subscribers
  • Views 463 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

TIDA-010030: Reversed charger protection circuit

Jeffrey Wright
Expert 2855 points
Part Number: TIDA-010030
Other Parts Discussed in Thread: BQ76200

Hello;

I'm unclear as to the functionality of what I "assume" is the reversed charger protection circuitry. If my assumption is incorrect, would you please explain the function of the two circuits involving Q22 and Q23?

1. If my assumption is correct, please explain the purpose of circuit involving Q22? I've typically only seen the DCHG fet disabled, but Q22 seems to be there to disable the charge fet. And if so (?), it couldn't anyway since the CHG fet's body diode would still conduct??

2. If a charger were connected, and both the CHG and DCHG fet's were OFF, it would seem that D40 would pass the charger's voltage directly to the 76200's DSG pin? Is that permissible?

Thanks

  • 0
    TI__Expert 3145 points

    Hi Jeffrey,

    1. The function of P-Channel FET Q22 is to speed up the charging FET turn off. When the CHG pin is low, the Vgs of charging FET will turn Q22 on and short G-S of charging FET. When CHG pin of BQ76200 is high, the D34 is conduct and Q22 is off status. The Vgs will be high and turn charging FET on. 

    2. The function of N-Channel FET Q23 is to avoid fault turning on of discharge FET when PACK+ is negtive to PACK-. D42 will conduct and then Q23 will be turned on, thus short G-S of discharge FET. 

    3. the recommended maximum voltage of bq76200 DSG pinn is 75V. and when discharge FET off, DSG pin voltage is nearly PACK voltage. So, it should be ok. 

    Best Regards,

    Ryan Tan

  • 0 in reply to Ryan Tan
    Expert 2855 points

    Thanks Ryan;

    Ok, Would you be so kind as to review the attached initial schematic and suggest corrections/improvements? Note that it uses 2 bq76200's, each driving a bank of 8 AUIRF7759L2 Mosfets.  Note that there are a total of 8 discharge FET's and 8 charge FET's in parallel. I did this because of the FET's very large Qg (300uC max), which means an approx. max ~2.4uC, and another E2E post regarding the 76200's max drive capability indicated that this was beyond its capability.

    THanks

    Disconnect 2x 76200 RevChg Prot.pdf

  • 0 in reply to Jeffrey Wright
    TI__Expert 3145 points

    Hi Jeffrey,

    I am looking at the schematic and will give you some feedback few days later.

    I think email might be a better way to discuss this. here is my mail address: ryan_tan@ti.com. 

    Kindly please share below information about this project? 

    Your company name? Application of this project? Run rate per year? 

    Best Regards,

    Ryan Tan