Design Considerations for USB PD-Compatible Devices

USB Power Delivery (USB PD) is a standard that enables high-power delivery and is widely adopted in devices requiring fast charging and high power supply. Since 2024, with the EU mandate for USB-C and the advancement of USB PD 3.1 (EPR) support, the requirements for design have become even more stringent. This article explains the latest key considerations when designing USB PD devices.

[1. Understanding USB PD Specifications and Protocols]

USB PD is defined by USB-IF, with expanded functionality in each version. It is particularly important to understand the following points.

Maximum Voltage and Current

USB PD 3.1 (EPR) supports up to 240W (48V, 5A).

AVS (Adjustable Voltage Supply) / PPS

Continuous adjustable voltage supply enables more efficient charging and reduced heat generation. It is particularly essential for devices with built-in batteries.

Protocol Handshake

Reliable implementation of PD communication is required, and the design must properly handle EPR negotiation (EPR_Mode, KeepAlive, Exit, etc.).

[2. Power Management and Thermal Design]

To suppress heat generation and efficiency loss associated with high power, optimizing power design is crucial.

• Power IC selection: Adopt highly efficient DC-DC converters and PD controller ICs. In recent years, GaN (gallium nitride) devices have become mainstream. Thermal countermeasures: In addition to heat sinks and thermal pads, emphasis should be placed on PCB heat dissipation design.
• Capacitor optimization: MLCCs are effective for high-frequency ripple suppression, while conductive polymer capacitors are suitable for low-frequency fluctuation and acoustic noise suppression.
• Current limiting circuits: Provide overcurrent protection to ensure safety during abnormalities.

[3. PD Communication Implementation]

USB PD communicates via the CC (Configuration Channel) line. Consider the following to ensure reliability.

• PD controller selection: Choose standalone or MCU-integrated types depending on the application.
• Proper firmware development: Implement software compliant with the latest standards (PD 3.1/EPR).
• Signal quality assurance: In addition to optimizing CC line routing and noise countermeasures, compliance with EPR signal requirements is also important.

[4. Connector Selection]

Connector selection With higher power levels, requirements for USB Type-C connectors and cables have become more stringent.

• High-current compatible connectors: Select high-quality Type-C connectors supporting 48V and 5A.
• Durability verification: Evaluate mechanical reliability assuming frequent insertion and removal.
• E-Marker cable support: The design must correctly identify cables equipped with E-Marker, which are required when supplying 5A (up to 240W class) power.

[5. Safety and Compliance with Safety Standards]

To ensure the reliability of USB PD devices, robust protection circuits and certification-compliant design principles are essential.

• Overcurrent and overvoltage protection: Shutoff mechanisms using FETs or fuses during abnormal conditions.
• Temperature monitoring: Control heat generation using thermistors and temperature sensors.
• Surge and soft-start functions: With EPR high-voltage support, prevent voltage fluctuation surges and terminal damage.
• Communication protocol: Through built-in communication protocols and control functions, the charger communicates with the device and then provides controlled charging output.
• Power standards: Products design requirements, ambient temperature, and maximum power during prolonged use are all designed based on strict specifications and standards.

[6. Matching with Power Supplies and Measures Designers Should Take]

Compatibility with power supplies affects device stability and reliability.

• Multi-profile support: In addition to 5V/9V/15V/20V, consider 28V/36V/48V for EPR support.
• PPS/AVS support: Achieve efficient charging and suppress heat through fine voltage control.
• Fallback function: Switch to USB 2.0/BC mode or PD3.0, 2.0 mode if PD communication fails.
• Actual device verification: Conduct connection tests with various commercially available PD adapters to confirm compatibility.
• E-Marker detection processing: Correctly recognize required cables to avoid excessive power requests.

[7. Key Points When Selecting Recommended Power Adapters]

When specifying recommended adapters as part of the Products, confirm the following points.

• Matching output profiles: Whether the adapter supports the required voltage and current of the device.
• PPS/AVS support: If the device is designed to utilize it, adapter support is also essential.
• Market track record: Select adapters with verified compatibility.
• Protection functions: Choose high-quality products equipped with overvoltage, overcurrent, and short-circuit protection.

[8. Summary]

When designing USB PD-compatible devices, compliance with the latest standards (PD 3.1/EPR and AVS), adoption of GaN devices and appropriate capacitors, support for E-Marker cables, and conformity with European regulations are required. Designs based on these considerations enable stable operation and high compatibility, leading to improved user satisfaction and market competitiveness.

To deliver high-quality USB PD Products, prioritize designs that emphasize compliance with the latest standards and validation in real-world environments. Achieving high-quality USB PD Products requires not only compliance with standards and strong design and technical capabilities, but also rigorous validation based on real-world conditions.