SLVSEW8B August 2019 – December 2019 TPS66020 , TPS66021
PRODUCTION DATA.
For a hub application, the hub may be supplied by an external power source that is supplying power to a Host (via the Source path of the dual-role power (DRP) of the hub), as well as, a downstream Bus Powered Device (BPD) (DFP Source to the BPD). A communication path is formed from Host to the Bus Powered Device. Prior to FRS, power flows from the external power source to the Host and the Bus Powered Device. If the external power is removed, FRS operation will attempt to change the power role of the Host to a Source and the hub DRP port to a Sink allowing power to change direction from the Host to the BPD in an attempt to maintain the connection. It should be noted that after FRS, the contract is 5 V. Refer to the PD3.0 specification for further details on the Fast Role Swap function.
Two PD controllers are used in the FRS process. One PD controller resides on the Host side (USB PD Capable Host); the other resides on the hub side (USB PD Capable Hub). Both PD controllers are DRP since they must support power role swapping. Prior to FRS, the Hub DRP is a Source (known as the old Source) and may be supplying power to the DRP Host, which is acting as a Sink (known as the old Sink). After FRS, the Host DRP is a 5-V Source (known as the new Source, old Sink), and is supplying power to the Hub DRP configured as a Sink (known as the new Sink, old Source).