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BQ25700A: What external USB parts for power negotiation are needed?

Brian Antheunisse
Expert 5305 points
Part Number: BQ25700A
Other Parts Discussed in Thread: BQ25700, BQ24392, HD3SS3220

Hi guys,

If using the BQ25700A  to charge a pack with USB as the input power source, what external chips are needed to enumerate with the upstream Dedicated Charging Port (so a simple brick adapter)? Normally this is done when the USB plug connection is made, the D+/D- lines get pulled down, and the pull down resistors on those lines usually tell the upstream power source what power to send. 

Now, if we are talking Type C PD, then the CC lines get involved so the upstream type C charger knows what power level to charge at.

When I look at the BQ25700, it says it supports:

  • 3.5-V to 24-V Input Operating Voltage –
  • Supports USB2.0, USB 3.0, USB 3.1 (Type C), and USB_PD Input Current Settings

I see nowhere for the D+/D- lines, or CC lines, to connect to directly with the device, leading me to believe that some external USB chips are needed here. 

Example, if they plan on supplying 12V on VBUS, will they need one of our PD controllers + USB power switches to sit between the USB connector and the BQ25700?

Thanks,

Brian 

  • 0
    TI__Mastermind 25800 points
    Hey Brian,

    That is correct; the charge controller itself does not have any detection mechanism, but is compatible with the standard current limits set by USB 3.1 and PD specs.

    Now, as far as detecting a DCP, consider using the BQ24392. This will require connection back to the Host who will then program the BQ25700A's input current limit. This works for USB 2.0 detection with BC1.2.

    And as you said, a separate PD controller would be needed to arbitrate and feedback to a host that will then program the BQ25700A. In terms of detection, I would refer you to the USB e2e forum for better suggestions. As I understand it, the Rp and Rd resistor divider will define the current capability of the Source port. One part you may want to look at is the HD3SS3220 DRP Port Controller, specifically the UFP functionality and current mode.


    Regards,
    Joel H