30-W/in3, 94% Efficiency, 65-W USB Type-C PD AC-DC Reference Design

This fully-tested, USB power delivery reference design from Texas Instruments is a high efficiency, high power density, ac-dc adapter solution with a wide input voltage range (85 - 265Vac) for laptop adapters and smartphone charger applications. It adopts active-clamp-flyback topology controlled by TI's newest ACF controller UCC28780 as the mainly power supply stage.

This design uses TPS25740B, TI's PD source controller, to achieve a full PD 2.0 function. The design achieves a peak efficiency of 94% at a very high switching frequency. The design's power density is increased to 30 W/in3, which is much higher than traditional solutions.

Smartphones and notebook PCs need adapters to charge their batteries. A USB-PD function makes charging convenient because the smartphone charger and notebook PC adapter are combined to one converter. High efficiency and high power density are required for the adapter to save power and make the device easier to carry. When the output power is lower than 75W, a PFC stage is not required.

This adapter reference design operates over a wide input voltage range from 85- to 265-Vac and must be able to power different equipment with different voltage demands automatically. When faults such as over-current, over-power, and over-voltage happen, the adapter reacts quickly to protect the terminal device.

Simplified block diagram (click on image to enlarge)

This reference design is a high efficiency, high power density, 65W output power USB-PD 2.0 ac-dc adapter that achieves a peak efficiency of 94% and a 30-W/in3 power density. The output is fully compatible with USB PD2.0 standard with 5V/3A, 9V/3A, 15V/3A, and 20V/3.25A outputs.

When an over-current, short-circuit, or over-power event occurs, this adapter reference design can cut off the output and recovery automatically. With over-voltage, the adapter is latched to avoid further damage to the terminal devices. Also, this adapter meets low no-load power consumption, which is less than 60mW.

This converter operates at a high switching frequency of 600 kHz (max), which helps decrease the size of the transformer and capacitors. Furthermore, the EMI filter is much simpler and smaller than low frequency converters.

Summary of features:

• High efficiency (94% peak value)
• High power density (30W/in³)
• Low no load power consumption (60mW)
• Low light load input power (0.5W), @20Vout/0.25W output
• Fully compatible with USB PD 2.0 standard, with 5V/3A, 9V/3A, 15V/3A, 20V/3.25A output
• Active-clamp flyback + SR topology
• Small size (62mm*28.6mm*18.4mm)

Overview of the UCC28780 controller

The UCC28780 is a high-frequency active-clamp flyback controller that enables high-density AC-to-DC power supplies that comply with stringent global efficiency standards such as DoE Level VI and EU CoC V5 Tier-2. User programmable advanced control law features allow performance to be optimized for both Silicon (Si) and Gallium Nitride (GaN) power FETs. Direct operation with switching devices that combine driver and GaN FETs is further enhanced with logic-level gate signals and enable outputs.

Zero voltage switching (ZVS) is achieved over a wide operating range with advanced auto-tuning techniques, adaptive dead-time optimization, and variable switching frequency control law. Using adaptive multimode control that changes the operation based on input and output conditions, UCC28780 enables high efficiency while mitigating audible noise.

With a variable switching frequency of up to 1MHz and accurate programmable over-power protection, which provides consistent power for thermal design across wide line range, the size of passive components can be further reduced and enable high power density.

UCC28780 works with VDS-sensing synchronous rectifier controllers, such as UCC24612, to achieve higher conversion efficiency and very compact designs.

UCC28780 features:

• Full and Partial Zero Voltage Switching (ZVS) of Primary FET with Adaptive Control
• Programmable Timing for External Si or GaN FETs
• High Switching Frequency up to 1MHz
• Programmable Adaptive Burst Control and Standby Mode for Light-Load Efficiency with Low Output Ripple and Audible Noise Mitigation
• Brownout Detection without Direct Line Sensing
• Accurate Programmable Over-Power Protection (OPP) to Support Peak Power Mode
• Fault Protections: Over-Temperature, Output Over-Voltage, Output Short-Circuit, Over-Current, and Pin Fault
• Direct Interface with Optocoupler Based Feedback Allows for Dynamically Scalable Output Voltage
• Internal Soft Start
• NTC Thermistor Interface with External Enable