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TPS65988: USB Power Passthrough: Fast Role Swap

Akash S
Intellectual 375 points
Part Number: TPS65988

Hi,

We are designing a system with Dual Port Type C USB. USB PD charger is planned to be connected to Port 1 whereas a battery powered device will be connected to Port 2.

The following are the use cases: 1. When the device is connected to the Port1 and no charger is connected in Port

1. the Power transfer is from VBUS2 to PPHV2 (act as a SINK) and then to the Buck to Power up the system.

2. Once charger is connected to Port1, then Port1 should be configured as SINK and request for a role swap of Port 2 as SOURCE and the Power transfers from VBUS1 --> PPHV1 --> PPHV2 --> VBUS 2. Also, it is branched after PPHV1 to supply the system.

3. Also, when the charger is disconnected from Port 1, a role swap request should be raised to configure the Port 2 as SINK again and draw power from the battery powered device.

Here, both the Port voltages are at 5V. Can the Role Swap (FRS) be achieved without any interruption to the System power supply?

  • 0
    TI__Mastermind 30000 points

    Hello Akash,

    I recommend following the power architecture outline in the TPS65988EVM. You can have the internal power paths sink power to your system, but you should use the external source path for port 2 connected to a dedicated supply like the EVM has. This is the best way to ensure your FRS is successful 

  • 0 in reply to Adam Mc Gaffin
    Intellectual 375 points

    Hi Adam,

    We don't have provision to connect external dedicated supply to our design.

    Anyway, the device connected to the port 2 is capable of sourcing.

    The app note SLVAE20 discusses on a similar implementation. Our board will be in place of the dongle discussed in the app note.

    So when the charger is disconnected at Port 1, we hope FRS happens and the Port 2 starts sourcing. Yes, this will cause some dead time. Is it possible to retain board operation during this period, using the charge stored in the bulk capacitors?

    And when the charger is connected, again we need a role swap at the Port 2.

    Please help us in figuring out if all this is feasible.

  • 0 in reply to Akash S
    TI__Mastermind 30000 points

    Hello Akash,

    If you system will be the dongle, then during the tests outlined in the SLVAE20 app note, it is the responsibility of the host system (not your system) to become the new source. Your device will be the initial source, but once power is removed, the host system your device will be connected to will become the new source.