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BQ24080: Battery polarity protection

Jonathan Navor
Genius 9475 points
Part Number: BQ24080
Other Parts Discussed in Thread: BQ25180

Hi Team,

Good day! I'm posting this on behalf of the customer.

Here it is:


I am using your BQ24080DRCR to charge a 4.2V lipo battery. I want to charge the battery iven if it is connecter with the opposite polarity. 

I see this circuit: 

Three questions: 

1) will this circuit work with the BQ?
2) what happen with the BQ (with this circuit) when i unplug the battery? 
3) what happen with the BQ ( with this circuit) when i unplug the USB ? 


Also, what happens with the BQ when i unplug the battery with this protection circuit? 


Best regards,

Jonathan

  • 0
    TI__Mastermind 19195 points

    Hi Jonathan,

    Jonathan Navor said:
    I want to charge the battery iven if it is connecter with the opposite polarity. 

    This is an interesting request, just so I understand:

    Normal polarity: Q2 / Q3 ON, Q1 / Q4 OFF

    Reverse polarity: Q1 / Q4 ON, Q2 / Q3 OFF

    1. It looks like this may work, you would still want to have primary protection for the battery to prevent undervoltage, overcurrent etc.. 
    2. BQ would charge its output cap up to the regulation voltage. 
    3. BQ stops charging

    The BQ acts like a current source up to the battery regulation voltage, should be able to simulate the circuit to see if it works. May also want to add series resistance to the gates to avoid ringing.

    It is possible to add reverse polarity protection, we have circuits for this you can refer to here: https://www.ti.com/lit/an/slva139/slva139.pdf

    Best regards,

    Nick

  • 0 in reply to Nick Brylski
    TI__Genius 9475 points

    Hi Nick, 

    Thank you for your support and sharing important details. I will update you once our customer have a follow up question. 

    Best regards,

    Jonathan. 

  • 0 in reply to Jonathan Navor
    TI__Genius 9475 points

    Hi Nick,

    Here is our customer's update. 

    1

    Nick Brylski said:
    It looks like this may work, you would still want to have primary protection for the battery to prevent undervoltage, overcurrent etc.. 

    -I thought the BQ has all those features right?

    2.

    Nick Brylski said:
    It is possible to add reverse polarity protection, we have circuits for this you can refer to here: https://www.ti.com/lit/an/slva139/slva139.pdf

    - In the document that you shared it seems to show a passive load (not a battery charger) if I use a battery charger I suppose that in have to connect the MOSFETs with the diodes pointing the load right?

    Best regards,

    Jonathan

  • 0 in reply to Jonathan Navor
    TI__Mastermind 19195 points

    Hi  Jonathan,

    Cell under voltage and over current protection is not possible due to bq24080 being non-powerpath, the system load is connected in parallel with the cells. A power path charger can include these features check out the BQ25180 (Buvlo, BATOCP).

    TI offers primary protectors such as this one: https://www.ti.com/product/BQ2970

    Jonathan Navor said:

    - In the document that you shared it seems to show a passive load (not a battery charger) if I use a battery charger I suppose that in have to connect the MOSFETs with the diodes pointing the load right?

    No changes are needed to the circuits in figure 2/3.. here is a drawing with charger included:

    Best regards,

    Nick

  • 0 in reply to Nick Brylski
    TI__Mastermind 19195 points
    Jonathan Navor said:
    1) will this circuit work with the BQ?

    It may work -- but worst case is that somehow a FET fails and you short BAT positive to BAT negative. Without any primary protection for the cells this would be a very fiery failure for the battery.