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BQ25170: Lithium Battery Protection using a TPS25961

Diane Eaker
Prodigy 30 points
Part Number: BQ25170

Tool/software:

I am trying to protect a lithium battery from an over voltage and over current when single fault failures occur on the battery charger.  If ISET on the BQ25170 is shorted, the current to the battery will exceed the CSA limit.  Our batttery can not see over 200mA; otherwise we fail CSA testing.  In the case that the BQ25170 IN to Out pins are shorted (again a single fault test that CSA will do), then the battery will see an over voltage (>4.2V).  i am trying to design a protectoin for the battery using the TSP25961 eFuse by putting the eFuse between the charger and the battery, but the charger wll not charge the battery when the eFuse is there.  if  i hook the battery directly to the charger (BQ25170), it works perfectly and charges as it should.  i have put togher a diagram of my circuit and wll attach it to this posting.  Can you advise me on a way to handle the battery protection.

  • 0
    TI__Guru 70776 points

    Hello

    It is common for Battery Packs to have a built-in protection monitor that will prevent over voltage and overcurrent.  Is this possibly present in yours?

    An example of a possible protection device is the BQ298xyz.

  • 0 in reply to Bill Johns
    Prodigy 30 points

    Hi Bill,

    Thank you for the reply.  Yes, our battery pack does have a protection circuit in it, but it is not UL approved; therefore, we need to have a "redundant" protection circuit on our board.  I did look at the BQ298xyz part.  I see it has a dev board available at Digkey which might be a good idea for me to buy today to understand the part.  But, a couple of questions after looking at the datasheet for this part.  

    1.  Our battery is 4.2V so I assume I would need the BQ298218 according to Table 4 in the datasheet, page 3.  Do you agree?  I see that part is has a lead time of 2/5/2025 which is not ideal.  Digikey lists parametric equivalents but they have higher OVP voltages, so I don't believe I could use those.  It puts us in a difficult position if the part is not available for prototype testing.

    2.  This question is somewhat related to the first.  I see the OVP delay is 1.25 seconds which seems long.  Is that acceptable for CSA?  I can't seem to get a solid answer out of our CSA contact, can you say anything about this?

    3.  We need the OCC (Over charge current) to be limited at 200mA.  Again, referring to Table 4, for the BQ298218, it shows -18mV and I don't understand what current that means.  I have not had a chance to dig deep in to the datasheet so can you answer?

    Diane

  • 0 in reply to Diane Eaker
    Prodigy 30 points

    I wanted to add that we are using the TI  BQ25170 Battery Charger just as an FYI.

  • 0 in reply to Diane Eaker
    TI__Mastermind 37700 points

    Hello Diane,

    For redundant protections, do you require all of the protections from the BQ298x? I have seen cases where simple OVP protectors are enough. 

    Diane Eaker said:
    1.  Our battery is 4.2V so I assume I would need the BQ298218 according to Table 4 in the datasheet, page 3.  Do you agree?  I see that part is has a lead time of 2/5/2025 which is not ideal.  Digikey lists parametric equivalents but they have higher OVP voltages, so I don't believe I could use those.  It puts us in a difficult position if the part is not available for prototype testing.

    The BQ297x could potentially also be used, if you'd like to see another device. You could also order the EVM and evaluate with somewhat different values from what you need, to understand how the device works.

    Diane Eaker said:
    2.  This question is somewhat related to the first.  I see the OVP delay is 1.25 seconds which seems long.  Is that acceptable for CSA?  I can't seem to get a solid answer out of our CSA contact, can you say anything about this?

    OVP typically has long delays, we have not seen any issues from our customers about this.

    Diane Eaker said:
    3.  We need the OCC (Over charge current) to be limited at 200mA.  Again, referring to Table 4, for the BQ298218, it shows -18mV and I don't understand what current that means.  I have not had a chance to dig deep in to the datasheet so can you answer?

    The BQ298x uses a sense resistor for current protections, typically this is a mOhm resistor placed in the low-side of the device. If the device detects a -18-mV voltage across the sense resistor, the protection would trigger. For the case of the 200-mA, you would require a 90-mOhm sense resistor.

    Best Regards,

    Luis Hernandez Salomon