Discover the path to ultra-cool, compact, and highly efficient fast charging with Pulsiv’s ground-breaking 65W USB-C reference design

The demand for USB-C is forecast to surge over the next decade, fuelled by the migration from USB-A to USB-C and a growing market of portable devices that require fast charging. As power requirements increase, the need to deliver more power in a confined space, so do the challenges of thermal management and heat dissipation which impact safety and reliability. The PSV-RDAD-65USB reference design has been developed to demonstrate how Pulsiv OSMIUM technology reduces component temperatures, enabling products to consume less power and reduce overall size. It represents the first in a series of designs aimed at pushing the boundaries of power conversion to create a sustainable platform for the USB-C standard.

In this design, the Pulsiv OSMIUM microcontroller PSV-AD-65EG-Q24IV has been combined with OnSemi’s NCP1342 Flyback controller and GaN devices from Innoscience to deliver a world-leading specification:

Taking ultra-cool operation & fast-charging to a whole new level

Critical components in conventional designs will often reach temperatures of over 100°C, so measures must be taken to dissipate heat or limit output power. This means compromising cost, performance, or physical size which can potentially impact safety and reliability.

Competitor data demonstrates the highest component temperature of 93.6°C

(A 65W USB-C reference design from a leading manufacturer of power supply solutions. NOTE: The thermal data shown has been taken from their datasheet in the public domain)

The Pulsiv OSMIUM reference design demonstrates a significant improvement in thermal performance and reduces critical component temperatures by more than 30% compared to other designs. At full load, the Flyback transformer reaches only 33.9°C at 230 V_AC and 30.3°C at 265 V above an ambient temperature of 26.1°C. This incredible achievement is likely to set a new benchmark and enable fast charging in space-constrained environments and/or heat-sensitive applications such as in-wall plug sockets that incorporate USB-C connectivity.

Setting a new benchmark in power conversion

Pulsiv OSMIUM technology provides a patented AC to DC front-end conversion method that applies intelligence to an active valley fill approach and delivers a combination of game-changing benefits in power electronics designs. It significantly improves performance at low loads to increase overall average efficiency, reduce energy consumption, and deliver a flat efficiency profile across all load conditions.

The Pulsiv AC to DC conversion method intelligently regulates the charging current and voltage on the storage capacitor using a high-side architecture to switch Q_ch. This allows the use of 200 V or 160 V capacitors (selectable) to support a universal mains input. The valley-fill period is broadly similar to a 2C3D architecture; but the charging period of the capacitor is significantly longer and more variable.

(Figure 1:  Pulsiv OSMIUM high-side architecture)

Reducing system losses

Figure 1 shows a simplified circuit implementation to illustrate the basic operation of Pulsiv OSMIUM in this design. A MOSFET, Q_ch, is used to control the charging of C_ch to generate a configurable high-voltage DC output (HVDC) and a blocking diode D_b ensures that C_ch does not discharge through the body diode of Q_ch while avoiding stray conduction through the inductor. This approach allows the use of smaller and lower-cost 200 V or 160 V capacitors to support a universal mains input.

Losses during the charging phase are typically between 0.5% and 2%, resulting in a peak efficiency of up to 99.5%. The circuit converts just enough energy to maintain capacitor voltage and delivers consistent efficiency over the full power range. 

In a traditional valley-fill design, AC to DC conversion involves a full-wave diode bridge. Diode losses are mainly determined by the average current, RMS current, the forward voltage drop, and the resistance during conduction. Conventional systems without power factor correction exhibit large peak currents, resulting in higher RMS currents and greater diode bridge losses. Power factor correction improves RMS current and results in a current waveform with a crest factor of √2. Pulsiv OSMIUM designs typically have a crest factor of 1.3, which is lower than that of a sinusoid, leading to lower RMS values and reduced losses. Peak line currents are reduced by up to 90% as a direct result of the way Pulsiv OSMIUM controls capacitor charging, and inrush current is also eliminated.

Optimize efficiency and space with a half-active bridge 

Pulsiv OSMIUM technology senses AC line voltage/frequency to adjust capacitor charging time and draws no line current at the AC zero voltage crossing. This enables a simple half-active bridge implementation to increase efficiency, especially at low-line conditions. MOSFETs in the lower half of the AC to DC bridge are carefully controlled and combined with high-side diodes. The half-active bridge in this design strikes the delicate balance between efficiency, cost, and complexity. It supports universal input with efficiency gains of 0.7% at full load from a 115 V AC supply.

(Pulsiv unique Half-Active Bridge Control)

Innovation in magnetics design reduces transformer size by 20% 

Pulsiv OSMIUM technology generates an HVDC output that varies between the peak AC input and 150 V (with a 230 V input) to drive the QR Flyback at maximum efficiency. The wide voltage range it generates requires a significantly reduced primary side inductance which enables the use of an EQ20 transformer. This was developed in partnership with magnetics experts Frenetic where a 20% size reduction was achieved compared to the typical RM8 used in other designs.

Minimizing losses with GaN optimization

GaN transistors from Innoscience have lowered R_DSon to reduce conduction losses, but this naturally increased parasitic capacitance. The INN700DA240B was selected to balance the two losses. The synchronous rectifier has also used an additional Innoscience GaN transistor INN150FQ032A. 

In this design, GaN lowered the overall energy consumption, reduced component size, and improved cost compared to conventional MOSFET’s. Innoscience also provided outstanding support, delivering samples within 48 hours, and demonstrating the most competitive pricing.

(Innoscience INN700DA240B)

(Innoscience INN150FQ032A)

Design package & evaluation boards 

The PSV-RDAD-65USB document package is available to download free from the Pulsiv website and includes a Datasheet, Schematics, Bill of Materials, & Altium files. A technical article has been written to provide more detail on this ground-breaking design supported by a white paper about the Pulsiv OSMIUM patented switching method. 

The PSV-EBAD-65USB evaluation board enables rapid lab testing and can be pre-ordered now for delivery in the 2nd half of August through a network of franchised distribution partners including global stockist Digikey.

Summary

The PSV-RDAD-65USB reference design showcases a truly sustainable approach to efficient power conversion, ultra-cool thermal performance, and reduced energy consumption in USB-C applications. It demonstrates how the Pulsiv OSMIUM technology can influence magnetics design while supporting GaN to minimize overall losses. Its game-changing thermal performance paves the way for fast charging in virtually any USB application. 

Fully assembled, size-optimized, and EMC-compliant “Plug & Play” modules of this reference design are currently under development to help accelerate adoption and simplify the design process. Many variants are possible and a 1C configuration can be pre-ordered through any of the franchised distribution partners for expected delivery in Q4 2024.