To convert an existing USB 2.0 device to Type-C, the designer must add two pull-down resistors to the CC pins and route the USB D+/D- signals to both positions on the Type-C receptacle. No other changes are required. The device waits for Vbus to be valid, enables it’s D+ pull-up resistor (for a Full Speed or High Speed product), Chirps (if High Speed device) and USB enumeration occurs as normal.
The USB Type-C cable allows two hosts to be connected together. A USB Type-C host cannot enable Vbus at all times like a Type-A host. Enabling Vbus at all times will cause two host Vbus supplies to be shorted. Only when a device pull-down resistor is detected does the host enable Vbus to the device. To convert an existing USB 2.0 host to USB Type-C, Vbus for each port must be switchable.
Additionally, pull-up resistor(s) and the capability to detect one of the device pull-down resistors must be added. Some host PHYs can use the VbusValid detector for detecting devices. Some host designs can use existing ASIC or SoC GPIOs with suitable over-voltage protection. Other host designs must investigate the use of external USB Type-C ‘add-on’ chips or modify the Power Management IC (PMIC) to support device attach detection.
This simplified USB 2.0 Type-C device and host implementation does not support high current charging, active cables, power delivery, analog audio adapter or debug accessories. The advantage is it is a cost-effective approach that does not require ASIC or SoC redesign and minimizes time-to-market.