9.2.2.9 Fast Role Swap (FRS) (Optional)

The TPS6602x supports Fast Role Swap operation as in the new Source, old Sink scenario shown in Figure 24. The PPHV power path represents the old Sink and the PP5V power path represents the new Source. During FRS, the PP5V power path of the TPS6602x has a much faster turn-on compared to normal operation, for example entering SRC 1P5A or SRC 3P0A states from the DISABLED state. This faster turn-on is required in order to meet the USB PD fast role swap timing requirements (tSrcFRSwap) for the new Source.

To enable FRS, the TPS6602x must first be operating as a Sink (SNK state). The TPS6602x must then transition to the FRS state by asserting EN1 high. EN1 is asserted high by the PD Controller as soon as possible once it has properly detected FRS signaling from its port partner on its CC line. The FRS signaling from the port partner to the PD Controller indicates that the port partner has lost its power and requires a fast role swap sequence to be performed.

It should be noted that the timing of when EN1 is asserted high relative to the port partner losing power is highly application, and implementation dependent. Some of these dependencies include:

• Loss of power detection accuracy, margin and propagation delay of the port partner.
• Timing from loss of power detection to FRS signaling transmitted on the CC line.
• Detection by the PD Controller of the FRS signaling received on its CC line.
• Assertion of a GPIO from the PD Controller after detection of the FRS signaling.

In systems that require good FRS performance, these should be optimized to minimize unnecessary delays from significantly impacting the turn-on of the new Source. Once the FRS state is entered, the TPS6602x will automatically handle the power role swap from Sink to Source as shown in Figure 25. In most applications, there is significant charge being stored in reserve while power is being provided. Upon loss of power, this charge is then used to supply power to the application until the FRS completes. As this charge depletes, the voltage on VBUS will decay at some rate based on the current load and the amount of charge that has been stored. USB PD requires that the new Source only be enabled once VBUS is detected below vSafe5V (maximum). Therefore, the amount of voltage that VBUS drops below vSafe5V will depend heavily on the amount of remaining charge and what current load is on VBUS, along with how fast the PP5V power path can enable. It should be noted that the PD Specification allows VBUS to be discharged completely to ground and is shown in Figure 32 typical response curve.