7.3.3 DFP (Downstream Facing Port)

The TUSB422 can be used in applications in which USB devices are connected too. For example, in a desktop application the Type-C port(s) must be able to determine when a device is attached and enable both power (in the form of VBUS) and datapath (either USB data and/or Alternate Mode data like DisplayPort) to attached device. The TUSB422 can be used in a DFP application by programming the Role Control register to 0x05. This presents Rp on both of TUSB422 CC pins. When configured as a DFP, the TUSB422 can be used to control the sourcing of VCONN. Control of VBUS source path must be handled outside of the TUSB422.

Upon enabling TUSB422 for DFP, the TUSB422 will continuously monitor both CC1 and CC2 for a connection. After a connection has been determined, the TUSB422 will notify system of event by asserting the INT_N pin low. Upon detecting assertion of INT_N, the external microprocessor should read and clear the appropriate Alert registers.

The following steps are for initialization of the TUSB422 for DFP operation.

1. Upon TUSB422 power-up, the Power Status flag in Alert Register should get set indicating TUSB422 is initialized. When set, this flag will cause the INT_N pin to be assert low.
2. SW read the Alert Registers to determine reason for INT_N assertion. The expectation is Power Status bit (Reg10h bit 1) is set.
3. SW read Power Status register and notice that TCPC_INIT_STATUS flag is cleared. This indicates TUSB422 is ready.
4. SW clear Power Status bit in Alert register by writing a 1’b1 to the bit.
5. Program the TUSB422 to present Rp on both CC pins. This is done by writing 0x05 to the Role Control register. If advertising greater than default Type-C current is desired, then write 0x15 for 1.5 A current or 0x25 for 3 A current advertisement
6. Write Look4Connection command to the Command register.
7. The TUSB422 now presents Rp on both CC pins and look for a connection.