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BQ25798: Can a USB 5 V adapter charge a 3s battery pack ?

Hulu
Prodigy 30 points
Part Number: BQ25798
Other Parts Discussed in Thread: TPS25751

Tool/software:

Hi all,

For our embedded gaming system, we plan to use a 3s battery pack to power the system. We must charge the battery with a USB adapter and we need to configure the charger so that we can reach 3 A of charging current. So we're between the legacy USB charger and the USB PD. We haven't seen clearly whether BQ25798 is capable of creating a higher voltage (3s pack corresponds to 10.8 or 11.1 V) from the USB 5 V. In the datasheet it is indicated there are boost, bulk DC/DC, however, we need to be sure that BQ25798 can handle a 3s only with USB adapter as charging source.

Thanks a lot in advance.N

Warm regards,

Hulu

  • 0
    TI__Guru**** 155056 points

    Hi Hulu,

    The datasheet has efficiency graphs that show how much current you can get from 5V power for charging 3S battery as shown below. From a simple power balance of efficiency = Pout/Pin = 12.6V*3A / (VBUS*3A), even with efficiency = 100%, VBUS needs to be >12.6V.  I recommend USB-PD.  The charger cannot communicate directly with USB-C so you will need a USB comms chip.  We have a reference design with BQ25798 and TPS25751 at 

    https://www.ti.com/tool/USB-PD-CHG-EVM-01.

    Orange trace.

    Regards,

    Jeff