I want to utilize a USB Type-C connector to charge a single battery that powers a device. The device will only function as an upstream facing port (UFP) or sink and no data communication will need to occur using USB2.0, USB3.0/3.1, or Aux pins. What are the minimum components necessary (besides the Rd resistors) for the CC1, CC2, and VBus lines to use a USB Type-C receptacle to charge the battery off the VBus line? Will the source side recognize complete connection and orientation and know when to send 5V through to VBus or do I need to control that on the sink side?
According to the spec:
A DFP must implement a Rp pull-up resistor to 5.0V or 3.3V. When a DFP to UFP connection is made, a resistor divider is formed, and the voltage at the CC pin can be measured to interpret the type of connection.
TABLE 2: CC PIN VOLTAGE RANGES
- CC Pin Voltage
- 0.00V - 0.25V No connection
- 0.25V - 0.70V Legacy current (500mA for USB2.0, 900mA for USB3.0/3.1)
- 0.70V - 1.31V 1.5A capable
- > 1.31V 3.0A capable
If Rd=5.1k 1% then CC Vmax=2.04V
The standard power over Type-C link works in the following way.
If both ports are Type-C, the initial state of provider is no VBUS.
DEVICE: The device must have 5.1k pull-down on the its port CC pin (on both pins).
HOST: The host must have pull-ups on both CC pins, in accord with its capability. With pull-ups to 5 V, 56k pullup means standard capability (500/900mA), 22k pull-up means 1.5 A capability, and 10k for 3.0 A capability. Alternatively this advertising can be done by means of corresponding current source.
CABLE: A C-C cable must have a wire connecting CC pins between both ends.
Initially, if no connection is made, the host side sees high voltage on CC pin, and the device sees low (zero) on its CC pin.
CONNECTION: Once the C-C cable is connected between two link partners, the DFP (host) will sense the drag by 5.1k resistor (from device side). As result, it will turn the VBUS on. This is how a host recognizes that a connection has been made. The connect event is essentially controlled by sink side having 5.1k Rd.
The UFP (device), upon receiving VBUS, should measure the voltage on CC pin, and should set its expectations in accord with the table provided by Tony Stewart.
So, the CC pin level is "measured" on both ends of the C-C link, by the host to detect connection and enable VBUS, and by device to determine power capability of the host.
If a legacy connection is used, the advertising is done by legacy cable assembly, inside its Type-C end (overmold), indicating lowest power capability using 56k (since the cable doesn't know what kind of host it is plugged in).