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BQ25713: Use BQ25713 as buck boost power supply when no battery is present

Daniel Rebollo
Expert 1205 points
Part Number: BQ25713

Hi,

Sometimes my board has a battery and sometimes not, and I want to know if BQ25713  can be used as 4.2Vout buck-boost supply without battery (or replacing it with a capacitor to help in some current peak) and what is his RMS current output. Seeing datasheet diagram I think it will be possible, but I dont know if there is some other consideration.

Thanks

  • 0
    TI__Expert 3320 points

    Hi Daniel,

    Correct, BQ25713 can support non battery operation or replacing battery with capacitors.

    No battery case:  the steady state system output current is determined by VBUS input current limit which is 6.4A maximum, depends on the VBUS voltage and VSYS voltage you can estimate the maximum output current accordingly.

    With battery case: the steady state system output current is determined by above calculation result plus battery discharge current limit. Basically the full input power and battery discharge power are providing energy to the system giving you the highest output current.

    Regards

    Shishuo

  • 0 in reply to Shishuo Zhao
    Expert 1205 points

    1) I have BQ24780SEVM board and output is disabled without battery. Maybe this board don't work the same as BQ25713? (I will use BQ25713, but I have BQ24780SEVM in my lab so I tested with it).

    Or maybe there is some register I need to configure?

    2) So, if I understood you well, voltage regulation is working without battery. But, to what value? 4.2V?

    3) Can I put any standard capacitor like 470uF16V instead of battery?

    Thanks for your fast response

  • 0 in reply to Daniel Rebollo
    TI__Expert 3320 points

    Hi Daniel,

        1) BQ25713 can support system without battery for sure. You can try it on EVM. 

        2) The system voltage regulation is determined by system minimum voltage(REG 0D/0C) if no battery connected and inhibit charge. Default MinSystemVoltage register setting is 3.584 V for 1 S, 6.144 V for 2 S and 9.216 V for 3 S, and 12.288 V for 4 S.

        3) No problem, you can use 470uF cap, but please make sure the charge voltage(REG05/04H) is below 16V capacitor voltage rating.

    Regards

  • 0 in reply to Shishuo Zhao
    Expert 1205 points

    Great, I think this solved my questions but one more thing: how is the name of the hability to work without battery in a charger? I mean, I want to know how to look for it and know if a device can support it or not.

    Thanks

  • 0 in reply to Daniel Rebollo
    TI__Expert 3320 points

    Hi Daniel,

        

         Generally speaking, our chargers all support no battery application. You can assume capacitor at VBAT terminal as a small battery.

         But I assume you are referring to the capability to support separate VSYS and VBAT. Basically when battery is depleted and charger still be able to provide a separate minimum system voltage to support system. This capability is named "Power path management" shown in our data sheet below. Hopefully this answer your question.

     

    Regards