The TPS26750EVM is capable of functioning as a source, sink, or Dual Role Power (DRP) device, adapting to either power role based on the connection. When configured as a DRP device, it can initiate connections in either role (source or sink) but typically has a preferred role set. If the preferred role is set as “source,” yet it initially connects as a sink to a port partner, the TPS26750EVM actively requests a power role swap to attempt to assume the source role. To perform this test, the power supply and load needs to be switched out for two bi-directional power supplies.

Use the following guidelines to set up the EVMs for Power Role Swap test:

1. Follow the TPS26750EVM User's Guide and TPS26750 Web Application to configure the two TPS26750 EVM's as DRP with no preferred role set.
   Note: The BQ25756EVM has a default charge voltage of 29.4V. In order to see the full EPR range, the voltage divider on the BQ25756 FB pin needs to be changed to support a higher charger voltage or the charge current needs to be increased to 8A. On the source side the power supply on the source side is fed from the J8 connector of TPS26750 into the battery terminal of BQ25756. The voltage on the power supply needs to be proportional to the charge voltage programmed using the voltage divider on the BQ25756 FB pin.
2. Connect the J1 and J7 mating connectors of the TPS26750EVM to the reciprocal connectors on the provided BQ25756 interposer board.
3. Insert the other side of the BQ25756 interposer board to headers J1 and J3 on the BQ25756EVM. Make sure the prongs are inserted all the way into the headers.
4. Attach one end of the ribbon cable to header J9 on the TPS26750EVM, attach the other end of the ribbon cable to header J8 of the BQ25756EVM.
5. Repeat steps 1-4 for the other set of EVMs
6. There should be two combination of EVMs, both configured as DRP.
7. Connect the bi-directional power supplies to the J8 ports of the TPS26750 EVM's.
8. Turn the bi-directional power supplies on.
9. Use a USB-C cable, capable of EPR, to connect the USB-C terminal J4 of the source board to the USB-C terminal J4 of the sink board
10. The two TPS26750 begins negotiating to establish a PD contract. If the power supply, load, and USB-C cable are capable of EPR. The VBUS of the PD controller goes to 5V, then 20V, then 48V.
11. After the two set's of EVM's establish a power role connection, a 4CC command can be sent to either of the TPS26750EVM's to perform a power role swap.

Figure 2-5 48V/5A 240W EPR PRS Swap From Source to Sink

The device starts as a source, the host then request a PRS to sink, using 4CC command. The VBUS drops from 48V to 0V and then ramps up from 0V to 5V, then 5V to 20V, and then 20V to 48V. The CC lines show that the PD controllers are communicating with each other. IBAT/VBAT shows the device sourcing at 8A in the beginning, dropping to 0A during the PRS, and then sinking at 8A.