USB Type-C® and USB Power Delivery (USB PD) have become the universal standard for powering everything from smartphones and tablets to laptops, monitors, docking stations, and industrial equipment. As power requirements continue to increase, the USB ecosystem faces new challenges in efficiency, thermal management, interoperability, and battery performance.
To address these challenges, the USB Implementers Forum (USB-IF) introduced one of the most significant updates to USB Power Delivery in recent years: Adjustable Voltage Supply (AVS).
While AVS was initially introduced in PD 3.1 as an advanced capability for Extended Power Range (EPR) devices, USB PD 3.2 elevates its importance by making Standard Power Range (SPR) AVS mandatory for USB-C® chargers above 27W, based on the port’s maximum power capability. For charger manufacturers, USB PD silicon vendors, system designers, and compliance engineers, this fundamental shift requires immediate attention.
The Evolution of USB Power Delivery
Traditional USB PD relies on Fixed Supply Power Data Objects (PDOs), allowing chargers to advertise standard voltages such as 5V, 9V, 15V, and 20V. During power negotiation, the sink selects one of these fixed voltage levels.
While effective for lower-power applications, fixed voltage operation becomes increasingly inefficient as charging power scales up. Devices frequently require operating voltages that sit precisely between these predefined values, forcing internal DC-DC converters to dissipate the excess energy as heat.
For example:
- A device may need exactly 13.8V but is forced to receive 15V.
- A laptop battery may require 16.5V while receiving 20V.
The cascading results of this mismatch are higher conversion losses, increased thermal stress, reduced charging efficiency, and an additional burden on internal battery management systems. As USB-C® expands toward 100W and 240W operation, mitigating these inefficiencies is critical.
What is Adjustable Voltage Supply (AVS)?
Adjustable Voltage Supply (AVS) enables a USB PD source to provide a continuously adjustable output voltage rather than being constrained to strict, fixed voltage tiers.
Instead of being limited to 9V, 15V, or 20V, an AVS-capable source can provide highly specific voltages (e.g., 9.2V, 10.7V, 13.5V, 17.8V) in precise 100mV increments. This allows the source to perfectly match the actual operating voltage required by the sink device's internal power rail.
The resulting benefits include:
- Dramatically improved system-level efficiency
- Significantly reduced heat generation within the sink device
- Better long-term battery health and charging performance
- Optimized thermal headroom for high-performance operations
USB PD 3.2 Introduces a Major Compliance Change
One of the most consequential updates in USB PD 3.2 is that AVS is no longer an optional premium feature. USB PD 3.2 introduces mandatory SPR AVS requirements based on the port’s maximum Power Data Profile (PDP). Crucially, the implementation of SPR AVS eliminates the need for optional fixed voltages above 9V, streamlining the negotiation process.
SPR AVS Requirements
Supporting up to 100 W of continuous VBUS loading and sourcing is essential for USB-PD validation at the upper limits of the specification. Emissions typically increase with higher current flow due to larger di/dt transitions and higher magnetic field strength in power paths.
| Port Maximum PDP | AVS Requirement |
| ≤ 27W | AVS not required |
| 27W < PDP ≤ 45W | 15V AVS required (9V–15V AVS range) |
| 45W < PDP ≤ 100W | 20V AVS required (9V–20V AVS range) |
In practical terms, this means that any 30W, 45W, 65W, or 100W charger must now support AVS functionality to achieve USB PD 3.2 compliance. AVS has officially transitioned from a niche feature to a core compliance pillar for higher-power Standard Power Range (SPR) USB-C® chargers.
AVS vs. PPS: Understanding the Difference
Engineers frequently compare AVS with Programmable Power Supply (PPS). Although both technologies offer dynamic voltage adjustment, they are engineered for fundamentally different operational goals.
PPS (operating in fine 20mV steps) was designed primarily to talk directly to a smartphone battery to manage charging thermals. AVS (operating in highly stable 100mV steps) is designed to optimize the efficiency of the entire system's input voltage, scaling all the way up to large devices like laptops and industrial equipment.
| Feature | Programmable Power Supply (PPS) | Adjustable Voltage Supply (AVS) |
| Introduced | USB PD 3.0 | USB PD 3.1 (EPR) & 3.2 (SPR) |
| Primary Focus | Smartphone battery thermal management | System-level efficiency & universal delivery |
| Voltage Range | 3.3V to ~21V | 9V to 48V (SPR: 9–20V, EPR: 15–48V) |
| Voltage Increments | 20mV | 100mV |
| Maximum Power | 100W | 240W |
| EPR Support | No | Yes |
Industry Impact
For Charger Manufacturers
AVS support dictates significant hardware and firmware design considerations:
- Firmware & VIFs: Controllers must advertise AVS capabilities (APDOs) correctly and generate accurate Vendor Information Files (VIFs).
- Power Supply Design: Voltage regulation accuracy and dynamic transition timing must remain stable across the entire supported AVS operating range.
- Certification: AVS introduces strict new compliance testing parameters that must be cleared prior to market release.
For Silicon Vendors
USB PD controller and power management IC vendors must guarantee support for AVS APDO advertisement, dynamic voltage transitions, strict regulation accuracy, and broad sink interoperability to pass USB-IF certification.
For Product Developers
Developers of smartphones, AI laptops, monitors, docking stations, and automotive USB-C® systems must ensure their sink devices can smoothly interoperate with AVS-capable sources. Products clinging to legacy fixed PDO assumptions risk widespread interoperability failures in the evolving ecosystem.
Why AVS Matters for Compliance Testing
AVS introduces significantly more rigorous validation requirements than traditional Fixed PDO operation. Manufacturers are now required to verify:
- Capability Advertisement: Ensuring APDO reporting adheres to PD 3.2 logic.
- Voltage Accuracy: Validating output across the continuous AVS range.
- Transition Timing: Verifying strict timing tolerances during dynamic 100mV voltage steps.
- Regulation Performance: Confirming unwavering stability under dynamic load conditions.
Failure in any of these areas will result in hard certification failures or severe interoperability issues in the field.
How GRL Platform Solutions Helps Validate AVS Compliance
As USB PD transitions to dynamic voltage paradigms, comprehensive compliance and interoperability testing is non-negotiable. GRL Platform Solutions provides the definitive validation ecosystem for USB Power Delivery development and certification.
- GRL C2-EPR USB-IF Compliance Tester: The C2-EPR platform enables manufacturers to rigorously validate USB Power Delivery compliance requirements, automatically executing AVS-related functionality testing for official USB-IF certification.
- GRL V-DPWR-EPR Functional & IEC Conformance Tester: The V-DPWR-EPR platform delivers deep functional validation, advanced protocol analysis, and IEC conformance testing for complex USB PD implementations.
Together, these platforms empower developers to accelerate time-to-market while guaranteeing flawless compliance with the latest USB PD 3.2 mandates.
Why AVS Readiness Can’t Wait
The USB PD 3.2 mandate requiring SPR AVS for chargers above 27W is not merely a minor specification update, it is a fundamental architectural shift. By enforcing precise voltage control, the USB-IF is aggressively driving improved efficiency, reduced thermal waste, and better battery performance across the entire hardware landscape. Organizations developing USB-C® products must evaluate their AVS testing and compliance readiness today to secure their position in the next generation of intelligent power delivery.
