⚡️ Key Implementation Notes
1. Power Configuration & CC Pins
The magic of USB-C lies in the Configuration Channel (CC) pins: CC1 and CC2. These pins are used to detect plug orientation, establish the power relationship (source or sink), and negotiate power capabilities up to 240W via the USB Power Delivery (PD) protocol. The basic configuration is set by pull-up (Rp) or pull-down (Rd) resistors.
Acting as a Power Source (Host/Charger - DFP)
To provide power, a host or charger (Downstream Facing Port) must pull up bothCC1 and CC2 to a 5V supply through Rp resistors. The value of Rp advertises the default current the source can provide:
- 56 kΩ for Default USB Power (500mA / 900mA)
- 22 kΩ for 1.5A capability
- 10 kΩ for 3.0A capability
Acting as a Power Sink (Device - UFP)
To draw power, a device (Upstream Facing Port) must pull down bothCC1 and CC2 to Ground through Rd resistors. The standard value for Rd is 5.1 kΩ. The device then monitors the voltage on the CC lines. Only one will be connected through the cable, and its voltage level indicates the source's current capability.
2. High-Speed Data Lines (TX/RX Pairs)
The SuperSpeed data lines (TX1+/-, RX1+/-, TX2+/-, RX2+/-) are high-frequency differential pairs. For correct signal integrity on a PCB:
- They must be routed as matched-length pairs.
- They require a controlled differential impedance, typically 90Ω ±10%.
- Keep them away from noisy sources and ensure a solid reference ground plane underneath.
3. Connector Shield
The metal shield of the connector is crucial for EMI (Electromagnetic Interference) and ESD (Electrostatic Discharge) protection. While it must be connected to ground, a direct, hard connection to your signal ground is not always the best practice. A common and robust approach is to connect the shield to the chassis ground via a parallel resistor (e.g., 1 MΩ) and a capacitor (e.g., 1-10 nF). This provides a path for ESD while separating high-frequency noise from the signal ground.