Points to note in the design of USB PD compatible devices

USB Power Delivery (USB PD) is a standard that enables high-power power delivery and is widely adopted in devices requiring fast charging and high power supply. From 2024 onward, with the enforcement of USB-C requirements in Europe and the advancement of USB PD 3.1 (EPR) support, the design requirements are becoming increasingly stringent. This article explains the latest considerations when designing USB PD devices.

[1.Understanding USB PD Specifications and Protocols]

USB PD is defined by USB-IF, and its features have been extended with each version. It is especially 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

By providing continuously adjustable voltage, more efficient charging and reduced heat generation are possible. It is particularly essential for devices with built-in batteries.

Protocol Handshake

Proper PD communication implementation is required, and designs must be capable of correctly handling EPR negotiation (EPR_Mode, KeepAlive, Exit, etc.).

[2.Power Management and Thermal Design]

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

• Power IC selection: Use high-efficiency DC-DC converters and PD controller ICs. Recently, GaN (gallium nitride) components have become mainstream. Heat management: In addition to heatsinks and thermal pads, importance is also placed on thermal diffusion design of the PCB.
• Capacitor optimization: MLCCs are effective for high-frequency ripple, and conductive polymer capacitors for low-frequency variations and squeal noise.
• Current limiting circuits: Equipped with overcurrent protection to ensure safety during abnormalities.

[3.Implementation of PD Communication]

USB PD uses the CC (Configuration Channel) line for communication. Consider the following for ensuring reliability:

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

[4. Connector Selection]

Connector Selection As power increases, requirements for USB Type-C connectors and cables have become stricter.

• High-current compatible connectors: Choose high-quality Type-C connectors supporting 48V and 5A.
• Durability verification: Mechanical reliability evaluation assuming frequent plug/unplug cycles.
• E-Marker cable support: Design must correctly identify E-Marker equipped cables required for 5A (max 240W class) power delivery.

[5. Safety and Regulatory Compliance]

Ensuring the reliability of USB PD devices requires robust protection circuits and standardized principles for compliance design.

• Overcurrent/Overvoltage protection: Shut-off mechanisms using FETs or fuses in case of abnormality.
• Temperature monitoring: Control heat with thermistors or temperature sensors.
• Surge/Soft-start features: To support high voltages in EPR, prevent surge voltage or terminal damage from voltage fluctuations.
• Communication protocol: Built-in communication protocols and control features ensure proper charger-device negotiation before supplying controlled output for charging.
• Power standards: Product design requirements, ambient temperature, and maximum power during extended use are all based on strict specifications and standards.

[6. Matching with Power Supplies and Design Measures]

Compatibility with power supplies directly impacts device stability and reliability.

• Multi-profile support: In addition to 5V/9V/15V/20V, EPR support requires 28V/36V/48V considerations.
• PPS/AVS support: Fine voltage control reduces heat and enables efficient charging.
• Fallback function: If PD communication fails, switch to USB 2.0/BC mode or PD 3.0 / 2.0 mode.
• Actual device testing: Verify compatibility by performing connection tests with various commercially available PD adapters.
• E-Marker detection: Ensure proper recognition of required cables and prevent overcurrent requests.

[7. Points to Consider When Selecting Recommended Power Adapters]

When recommending an adapter for a product, check the following points:

• Matching output profile: Verify that it supports the voltage and current required by the device.
• PPS/AVS support: Required on the adapter side if the device is designed to use it.
• Market performance: Choose adapters verified for compatibility.
• Protection functions: Select high-quality models with overvoltage, overcurrent, and short-circuit protection.

[8. Summary]

When designing USB PD-compliant devices, it is necessary to comply with the latest standards (PD 3.1/EPR and AVS), adopt GaN components and appropriate capacitors, support E-Marker cables, and ensure compliance with European regulations. By reflecting these points in the design, stable operation and high compatibility can be achieved, leading to improved user satisfaction and market competitiveness.

To offer high-quality USB PD products, proceed with design that emphasizes compliance with the latest standards and real-world verification. Achieving high quality USB PD products requires not only conformity with standards and design expertise, but also stringent testing based on actual use environments.