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TPS25751: Which pwr Rail for PP5V in OTG Source Mode with BQ25638

Paul Budich
Prodigy 10 points
Part Number: TPS25751
Other Parts Discussed in Thread: BQ25638,

Tool/software:

Hi,

we want to use the TPS25751D PD Controller and the BQ25638 Battery Charger for a Battery Device with USB-C PD for Battery charging and with OTG support to drive external devices.
We have some questions:


1. It looks like the BQ25638 does all the power path and current management by itself, so we dont really understand the usage of the powerpath fets in the controller, shouldnt it be possible to connect the BQ25638 VBUS directly to the USB-C Connector?

2. We dont want to use an extra Buck-Boost converter for 5V, because we dont need them on our Board. If our understanding is correct, the BQ25638 outputs in OTG Mode 5V to VBUS, how do we have to connect the BQ25638 and the TPS25751? Is it possible to just connect BQ25638 VBUS to TPS25752 PPHV and leave PP5V open?

So for Sink Mode the Connection is clear:

But for Source Mode we are nott shure, PPHV should be capable of driving the 5V to the USB-C Connector, but why do we need the PP5V then and how we have to connect it?

I hope you can help us, thank you very much!

BR

  • 0
    TI__Guru 64841 points

    Hello,

    The TPS25751 solution has been developed with the following battery charger components in mind:

    Paul Budich said:
    1. It looks like the BQ25638 does all the power path and current management by itself, so we dont really understand the usage of the powerpath fets in the controller, shouldnt it be possible to connect the BQ25638 VBUS directly to the USB-C Connector?

    Yes, it would be possible to connect the BQ VBUS to the connector.  The power path in the controller is redundant.  I think the concern or question is how the power path is controlled.  You would most likely need an external micro to read the status from the TPS25751 and then control the power path within the BQ part.

    Paul Budich said:
    2. We dont want to use an extra Buck-Boost converter for 5V, because we dont need them on our Board. If our understanding is correct, the BQ25638 outputs in OTG Mode 5V to VBUS, how do we have to connect the BQ25638 and the TPS25751? Is it possible to just connect BQ25638 VBUS to TPS25752 PPHV and leave PP5V open?

    The PP5V is needed to power PP_CABLE (VCON, whichever CC pin is not used for PD communication).  

    Regards,
    Chris

  • 0 in reply to Chris Sterzik
    Prodigy 10 points

    Hi Chris,

    Thank you for your answer.
    We want to use the BQ25638 because of its ultra low 1.5uA Quiescent current.
    The Host SoC would do the Communication with the Charger IC.

    So if i understand it correctly, we have to use an external 5V boost converter for PP5V, there is no other option?
    And if we want to use PD and the CC Pins functionality we have to power PP5V?

    BR

    Paul

  • 0 in reply to Paul Budich
    TI__Guru 64841 points

    Hello,

    Paul Budich said:
    So if i understand it correctly, we have to use an external 5V boost converter for PP5V, there is no other option?

    I will look into alternatives.  The end application will have the ability to source and sink 5V (ie no higher voltage negotiation)?

    Paul Budich said:
    And if we want to use PD and the CC Pins functionality we have to power PP5V?

    If the cc pins only establish the current (bias on cc) and USBC-PD communication is not needed, then we may be able to omit the PP5V.

    Regards,

    Chris

  • 0 in reply to Chris Sterzik
    Prodigy 10 points

    Hi Chris,

    The end application should source and sink up to 9V

    We need the USBC-PD Communication.
    Is it possible to source PP5V with VBUS from the BQ25638. Or doesnt it support the higher voltage?
    If not am i correct, that we have to use a boost converter from SYS for the 5V?

    I hoped we could avoid that.

    BR

  • 0 in reply to Paul Budich
    TI__Guru 64841 points

    Hello Paul,

    Paul Budich said:
    Is it possible to source PP5V with VBUS from the BQ25638. Or doesnt it support the higher voltage?

    The PP5V will not support 9V.  

    Paul Budich said:
    If not am i correct, that we have to use a boost converter from SYS for the 5V?

    The intended application is that a dedicated 5V is used to supply PP5V for sourcing applications.  My guess is that if you do not provide PP5V, then you will run into compliance and application issues where there is a cable which requires 5V.  It is possible that from an application perspective you would never need a cables active components because you are never going beyond 9V(3A) and there are no data capabilities.  The customer would need to take on the risk of not applying PP5V because this is stated as a recommended operating condition and therefore TI cannot assume any responsibility if the customer chooses to operate outside of that condition.

    Regards,

    Chris