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BQ24753A - no end of charging

Frank Thomas
Prodigy 195 points
Other Parts Discussed in Thread: BQ24753A, BQ24753, BQ24610

Hey guys,

I'm currently testing the BQ24753A.

While I was charging my LiPo battery (2 cells @ 8.34V, 5000mAh) I noticed that there is no charge cut off when the current is dropping below a certain value. I don't know the exact current limit for my battery but it is recommended as far as I know to cut off at 3% to 5% of the constant charging current (which is here 250mA and 3% would be then 7.5mA).

The manufacturer recommends after charging with constant current of 1.25A to cut off after additional 3.5h when 4.2V is received per cell. In this case the period is gone way beyond that limitation. I canceled charging manually after 10h (25h in total) of constant voltage charging and receiving a charge current of 6mA at the end.

So I was wondering because I wasn't able to find anything in the data sheet on which particular value this uC is relying or which cut off method it is using basically.

Does it e.g. depend on the set Charge Current Regulation, which is at the moment set to 3000mA or is there some kind of charge timer? Or do I have to cut off charging by myself with the help of the |CHGEN pin at the end!? Couldn't find an answer in the forum or in the data sheet.. so any help is appreciated.

regards, Frank

  • 0
    TI__Guru 56650 points

    bq2475x is a host control version charger IC. So, it doesn't control the termination current. The host controller or gas gauge IC should sense charger current and terminate the charger.

    A stand alone version charger IC has the termination function, for example: bq2461x; bq2417x.

  • 0 in reply to Wang5577
    Prodigy 195 points

    Thank you very much for fast and helpful answer.

    However I do not understand completely  why a host controlled charger IC shouldn't be able to detect taper current. But now I know for certain that the host IC will have to take care of it.

  • 0 in reply to Frank Thomas
    TI__Guru 56650 points

    bq24753 doesn't have a termination function. So, I call it a host control version. It means that the termination function is relied on the host controller. If a host controller can not detect the termination current or read the current out from the gas gauge, it can not disable the charger.

    bq24610 family IC has the termination function.