The term **PD-R** most commonly refers to **Power Delivery (PD) Receiving** or **Sink** circuits. These are the electronic components responsible for negotiating power from a USB-C Power Delivery source (like a wall charger) to power a device. --- ### 1. Core Electronic Components A PD-R system typically consists of several integrated circuits and passive components working together to handle high voltage and current. | Component | Function | Key Characteristics | | :--- | :--- | :--- | | **PD Controller (Sink)** | The "brain" that communicates with the power source via the CC lines. | Supports PD 2.0/3.0/3.1 protocols. | | **MOSFET (Load Switch)** | Acts as a gatekeeper to prevent high voltage from reaching the circuit until negotiation is complete. | Low $R_{DS(on)}$ to minimize heat. | | **CC Pull-down Resistors** | Two 5.1kΩ resistors on the Configuration Channel (CC) lines. | Signals to the source that a "Sink" is connected. | | **Buck/Boost Converter** | Adjusts the negotiated voltage (e.g., 20V) down to what the internal battery or logic needs (e.g., 3.7V or 5V). | High efficiency (>90%). | | **TVS Diodes** | Protects the sensitive PD logic from ESD (Electrostatic Discharge) and voltage spikes. | Fast response time, low capacitance. | --- ### 2. How the PD-R Negotiation Works The electronic interaction follows a specific sequence to ensure safety: 1. **Physical Connection:** The PD-R device uses **5.1kΩ resistors** on the CC1 and CC2 pins. This tells the charger to provide the baseline 5V. 2. **Communication:** The **PD Controller IC** sends digital packets over the CC line using Biphase Mark Coding (BMC). 3. **Capability Discovery:** The charger sends a list of "Source Capabilities" (e.g., 5V/3A, 9V/3A, 15V/3A, 20V/5A). 4. **Request:** The PD-R logic selects the highest compatible profile and sends a "Request" packet. 5. **Power Transition:** Once the "Accept" packet is received, the PD-R controller enables the **MOSFET switch**, allowing the high-voltage current to flow into the internal power rail. --- ### 3. Example Circuit Schematic Block Below is a conceptual representation of how these parts are wired: ```text [USB-C Connector] | |--[CC1/CC2]------> [PD Controller IC (e.g., CH224K / IP2721)] | | |--[VBUS]----------[ P-Channel MOSFET ]------> [System Load/Battery] | | (Gate Control) |--[GND]-------------------[Common Ground] ``` ### 4. Common PD-R Controller ICs If you are designing a circuit, these are the most common "trigger" or "sink" chips used: * **CH224K:** A popular, low-cost multi-protocol power sink chip. * **STUSB4500:** A standalone controller from STMicroelectronics, highly configurable via NVM. * **CYPD3177 (EZ-PD BCR):** Cypress/Infineon chip designed specifically to replace DC barrel jacks with USB-C. ---