What Is Preferred Power Supply (PPS)?

Preferred Power Supply (PPS) is a charging protocol extension defined within the USB Power Delivery 3.0 specification that allows a charger and a device to negotiate a continuously variable output voltage and current, rather than switching between a fixed set of discrete voltage profiles. By enabling fine-grained, real-time adjustment of the supply parameters, PPS allows device charging circuits to operate more efficiently and with lower heat generation than fixed-profile USB-PD predecessors. The protocol was standardized by the USB Implementers Forum (USB-IF) in 2017 as part of the USB PD 3.0 revision and has since been adopted in a wide range of smartphones, laptops, and portable electronics.

USB PD before PPS defined a set of fixed power profiles at 5, 9, 15, and 20 volts with discrete current steps. While useful, these fixed profiles forced device chargers to perform additional regulation internally, dissipating excess energy as heat. PPS addresses that limitation by allowing the charger to deliver precisely the voltage and current that the device's battery management circuit requests at each moment in the charging cycle.

Voltage and Current Negotiation

In a PPS session, the device and charger communicate over the USB Type-C configuration channel using the USB PD messaging protocol. The device periodically sends a Request Data Object that specifies the desired output voltage in 20 mV steps and the desired current limit in 50 mA steps, within a range from 3.3 V to 21 V at up to 3 A. The charger responds by adjusting its output to match, and the exchange repeats approximately every 10 seconds throughout the charging session. This continuous negotiation allows the charger to track the battery's acceptance as it moves through constant-current and constant-voltage phases, matching the supply precisely to what the battery and protection circuitry need at each stage. The USB-IF's official USB Power Delivery specification page describes the negotiation model and compliance requirements for PPS-capable chargers.

Thermal Efficiency and Battery Effects

The primary benefit of PPS is reduced heat at both the charger adapter and the device. Because the charger delivers a voltage already close to what the battery needs, the step-down conversion inside the device operates across a smaller voltage differential and dissipates far less power as heat. Manufacturers implementing PPS alongside direct-charge architectures, which route current from the USB-C port directly to the battery with minimal internal conversion, report significant reductions in device operating temperature during fast charging. The USB Power Delivery specification whitepaper from the USB-IF details the electrical requirements and the compliance test procedures that ensure charger output remains within the negotiated limits. Lower temperatures during charging have a direct positive effect on lithium-ion battery cycle life, making PPS charging protocols relevant to product longevity as well as user comfort.

Standardization and Interoperability

PPS is defined within the IEC 63002 standard, which the International Electrotechnical Commission adopted based on the USB Power Delivery framework. Compliance with PPS requires that chargers pass defined output regulation tests and that the negotiation protocol correctly handles error conditions, including voltage deviations and loss of communication. A primer on USB Type-C PD 3.0 from EDN covers the hardware design implications for charger developers implementing the PPS extension.

Applications

Preferred Power Supply has applications in a range of product categories and use cases, including:

• Flagship smartphone fast charging, where direct-charge architectures rely on PPS for precise battery-side voltage control
• Laptop and tablet charging, enabling single-cable power delivery that adapts across different load states
• Power banks and portable chargers, where PPS compliance allows efficient charging of multiple device types
• Automotive USB charging ports, where regulatory standards increasingly require interoperable PD implementations