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BQ25731: Reference design for USB-C OTG and PD, sink/source function, no additional DC-DC for 5V

Jan Zastera
Prodigy 250 points
Part Number: BQ25731
Other Parts Discussed in Thread: TPS54531, BQ25750, TPS25750

Hello,

I would like to ask you if there is some reference design for BQ25731 used for USB-C PD (OTG) and charging of battery (lithium 4 Cells) without using the next 5V DC-DC switching regulator for 5V. I found this: https://www.ti.com/tool/TIDA-050047 but there is next TPS54531. I think, 5V could be done from BQ25731, so is there something I am overlooking?

Below is what I mean, it seems, BQ25731 can do everything, no additional 5V DC DC is required, or am I wrong? Our product is really small, so every next DC-DC convertor brings us issues.

https://e2e.ti.com/blogs_/b/powerhouse/posts/adding-usb-type-c-with-power-delivery-to-battery-powered-applications-smaller-faster-fewer-components

Thank you very much.

Kind regards,

Jan Zastera

  • 0
    TI__Mastermind 25895 points

    Hi Jan,

    In the above mentioned design, 5V DCDC is needed for the PD device as its bias supply for startup, however, you can use a small device <5A.  

    Regards,

    Tiger

  • 0 in reply to Tiger Zhou
    Prodigy 250 points

    Hello Tiger,

    thank you for your response. On this link:

    e2e.ti.com/.../adding-usb-type-c-with-power-delivery-to-battery-powered-applications-smaller-faster-fewer-components

    block schematic does not include 5V DC-DC for startup in MCU based operation (our case). This is reason I asked. Maybe I overlooking something very important, but why I am not able to use BQ25731 IC to do 5V voltage for bias supply and then increase output voltage according USB-C demand?

    Thank you very much and kind regards,

    Jan

  • 0 in reply to Jan Zastera
    TI__Mastermind 25895 points

    Hi Jan,

    The PD device needs to be first powered on, before it can communicate with the BQ25731 to generate the 5V bias supply. The referred article link is just a conceptual drawing, not a real schematic. 

    Regards,

    Tiger

  • 0 in reply to Tiger Zhou
    Prodigy 250 points

    Hello Tiger,

    so if we use 5V dc/dc just for startup of TPS25750S and MCU, when it starts up is it possible to configure then BQ25731 to supply 5V output to USBC-PD purpose? In this scenario we could use some weak << 1A 5V DC/DC with small inductor which would fit our PCB much more easily.

    And second question is related to the fact, we need one non typical scenario in which we will have slot with external powering from some 12 - 20V (not decided yet, but not USBC-PD) 200+W power source, user will be able to fit up to four TPS25750S/BQ25731 based chargers in it in parallel and power them all together from that one non USBC-PD power source. In this case we need to get those non USBC-PD 12 - 20V to the BQ25731 through MOSFETs controlled by BQ25750S. And finally the question is: is it possible to enable this scenario to turn on external N-MOSFETs by writing to some BQ25750 registers? Or is there some other way to enable this scenario?

    Thank you very much

    Pavel

  • 0 in reply to Jan Zastera
    TI__Mastermind 25895 points

    Hi Jan,

    Correct! a small DCDC is Okay. 

    If the TPS25750 has some GPIO, it should be possible to do that. Please double check by re-submitting the question using TPS25750. 

    Regards,

    Tiger