How do I enable the legacy USB devices to be detected by a Type-C device?
To enable the legacy USB devices to be detected correctly by a Type-C device, connect one Rd resister between the GND and the CC pin. The recommended value of Rd in the Type-C specification is 5.1 kohm.
The figure below illustrates the functional model of this connection.
After connecting the legacy device to the Type-C source, the source can detect the pull-down on the CC pin because of Rd, and then the source will turn on VBUS and VCONN.