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BQ2982: Understand OVP

Søren Landgrebe
Prodigy 10 points
Part Number: BQ2982
Other Parts Discussed in Thread: BQ2970

Hello

I have started to develop a battery protection circuit, and decided to use BQ298215RUGR. 
The problem isn't the implementation but the OVP. I can read several places that a single lithium-ion battery can get damaged with higher voltage than 4.2V
The BQ298215 has a OVP (over voltage protection) at 4.440, isn't this way to high? 
I can't see in which application this will be used then, because all the lithium-ion batteries I have found is 4.2V+-0.3ish (like USE-18650-2600MAH)

Am I misunderstanding the term, or is this the wrong approach to a battery protector? 


  • 0
    TI__Mastermind 36240 points

    Hello Søren,

    There are a large number of battery chemistries, each with different requirements and full-charge/over-charges. Some high-capacity batteries can handle a higher voltage better, like 4.35-V or 4.4-V.

    Ideally your charger will charge the battery to the appropriate voltage before the BQ2982 does, but if this fails and the battery becomes over-charged, the protector will stop charging, 4.3-V may be okay in your battery but may likely worsen the lifespan of the battery. 

    The BQ298217 may better fit your requirements, this offers a 4.25-V protection, which is the over-charged state that is mentioned in your cell's datasheet. 

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 10 points

    Hi Luis 

    Thanks for your answer.
    I have looked at the BQ298217, but the tradeoff with that component is different OCC,OCD and SCD, and disabling off OT. Which means I cant get the same maximum charge current and discharge current.  Maybe I will try to look at something else, or just accept these tradeoffs. 


    Sure my charger circuit should develop 4.2 ass close as possible, but the risk is off course if something fails, and delivers a bit extra.  
    I'm still a bit confused on where "4.3-V may be okay" is decided. Not to accuse you, I've seen several circuits where that's the IC OVP, but the battery states 4.2V.
    Is that just a rule off thumb?

    I'm quite new into batteries, and quite concerned about damaging the battery, as I earlier has witness a room after a battery explosion. Don't wanna force that for sure. 

    Best Regards 

    Søren Landgrebe 

  • 0 in reply to Søren Landgrebe
    TI__Mastermind 36240 points

    Hello Søren,

    The OT protection is based on the internal die, there are no devices released of this family that have external OT protection. 

    Yeah, it is somewhat unfortunate that the OCC/OCD/SCD ratios are different. But the overall levels can be adjusted by adjusting the sense resistor value. If these do not work, you could also try looking at the BQ2970 (Which has low-side drive) instead and see if this would better fit your requirements.

    Søren Landgrebe said:

    Sure my charger circuit should develop 4.2 ass close as possible, but the risk is off course if something fails, and delivers a bit extra.  
    I'm still a bit confused on where "4.3-V may be okay" is decided. Not to accuse you, I've seen several circuits where that's the IC OVP, but the battery states 4.2V.
    Is that just a rule off thumb?

    No worries! This is a very valid concern. Apologies for the confusion, the "4.3-V may be okay" was more of a general statement. Some batteries could be charged higher than what their datasheets specifies, however, this can cause a steep decrease in the lifetime/number of cycles of the battery. At 4.3-V some batteries may still be safe (it would not catch fire/explode), albeit the lifespan of the battery would likely be greatly decreased if it was not rated for this voltage. To know exactly for your battery cells, it would be best to contact your battery manufacturer and see if they can tell you what risks there are with your particular cell.

    Based on the datasheet spec I saw on your battery; I would say 4.25-V is a "safe" place for the battery to overcharge. I would not go above what your datasheet recommends, as we do not know exactly what could happen otherwise. 

    Best Regards,

    Luis Hernandez Salomon