• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 65 subscribers
  • Views 628 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.

BQ2970: Is it required reverse battery protection?

Nikos Antoniou
Intellectual 820 points
Part Number: BQ2970
Other Parts Discussed in Thread: BQ25100,

Hi everyone,

I have included the BQ29707 battery protection into my design and I am considering if I have to protect the IC against reverse battery connection. For that reason I connected a P-Channel MOSFET on BAT pin as shown below. Is this required or should I omit the MOSFET?

  • +1
    TI__Intellectual 2146 points

    Hi Nikos,

    It seems like that could work. You may want to consider placing a high-value (5.1M) resistor between gate and source to discharge the gate, similar to what you did with the charge and discharge FETs. It'll dissipate a little more power during normal operation though.

  • 0 in reply to Albert Anwar
    Intellectual 820 points

    Thank you for your reply Albert!!

    My initial question was if the MOSFET is required. I mean, do I have to include reverse battery protection OR the BQ29707 provides reverse battery protection itself? 

    I will combine the BQ29707 battery protection with the BQ25100 battery charger and I have connected both ICs with the Vbat power signal. Is the battery going to be charged normally? or somehow the MOSFET will affect/disrupt the charging process?

  • +1 in reply to Nikos Antoniou
    TI__Guru 54715 points

    Hi Nikos,

    The BQ2970 does not provide reverse battery protection.  BAT can not go negative., similarly V- can not go above BAT.  Your extra FET seems it should work for a reversed cell.

    When used with the charger the cell is protected by the BQ2970 from over charge or over discharge.  Normally the BQ2970 will be "on" in normal mode and the charger can provide current and the load use current from the battery as needed.  If the charger does not behave properly and overcharges the cell the BQ2970 will protect.  Similarly if the load does not stop when the cell is discharged to its normal limit the BQ2970 will protect to disable further discharge.  Connecting the charger will cause a recovery from the overdischarge. 

    Your diagrams seem generally correct, the 5M at the charge FET should generally be from gate to source of the FET

  • 0 in reply to WM5295
    Intellectual 820 points

    Thank you for your assistance WM5295,

    WM5295 said:
    Your diagrams seem generally correct,

    Thank you to verify that!! My concern was if the MOSFET will effect the wireless charging as it is connected

    WM5295 said:
    the 5M at the charge FET should generally be from gate to source of the FET

    You mean like this?

  • +1 in reply to Nikos Antoniou
    TI__Guru 54715 points

    Hi Nikos,

    The reverse charge FET should always be on when the cell is connected properly.  If the cell degrades to be less than VGSTH of the FET it will become a diode and you won't be able to charge.

    Yes, the new placement looks more common.