USB-PD technology provides high charging performance to devices
Recommended adoption of ZVS/ZCS capable flyback topology
EMI can be reduced by selecting the right package for the product.


Today, we use a lot of devices that run on rechargeable batteries, including smartphones, tablets, laptops, and wireless headphones. However, having to use separate chargers and cables for each device can be quite inconvenient.

What if you could reduce the number of chargers and cables to one, and charge faster? What makes this possible is 'USB-PD (Power Delivery).' USB-PD is a charging technology that can be used on all devices.

From a technical standpoint, form factors, charging power, battery capacity, and charging times continue to improve. To keep pace with this, power density and efficiency must increase. This requires the use of a variety of topologies and power technologies.


A solution suitable for fast charging
First, let's look at the topology. The flyback, which is the most widely used in charger design, is cheaper and easier to design than other topologies. However, traditional flyback converters use large transformers to store energy. Therefore, it limits the maximum achievable power density.

A solution to overcome the limitations caused by transformer size is to increase the switching frequency. However, as the frequency increases, the energy loss of parasitic elements (mainly transformer leakage inductance) and MOSFET capacitance becomes significant.

To solve the problems caused by high switching frequency, a modified soft switching flyback topology is gaining popularity. For example, digital forced frequency resonance (FFR) can be used. Infineon's 'XDPS21071 and XDPS21081 digital controllers' can be used for this topology.

Recently, soft-switching flybacks have been incorporated into GaN (gallium nitride)-based devices to achieve higher switching frequencies and overcome the limitations of high-power density adapters by recycling energy from parasitic elements and reducing the transformer size.

However, high switching frequencies come with their own challenges. Fast switching frequencies pose challenges in terms of EMI. Also, in markets where system cost is sensitive, specialized devices such as GaN power switches and ZVS (zero voltage switching) controllers are expensive.

Asymmetric duty cycle flyback converters combine flyback and forward converters to address the challenges associated with high-density adapters operating at intermediate switching frequencies. It enables ZVS and ZCS (zero current switching) across the line and load range, enabling higher efficiency.

To help design engineers achieve their design goals, Infineon offers a comprehensive portfolio of semiconductor products including high-voltage and low-voltage power MOSFETs, USB-PD protocol products, and digital soft switching controllers that achieve high power density.


Choosing the Right USB-PD Controller
The charger market is largely end-user oriented, price sensitive and performance oriented. Infineon recommends the '2-chip PAG1 solution' with an excellent price-to-performance ratio for designs requiring efficiencies of 91% or more.

The solution consists of the 'PAG1P primary-side startup controller' and the 'PAG1S single-chip secondary-side controller' that integrates synchronous rectification control and USB-PD protocol control. In particular, the PAG1S is highly flexible as a programmable device.

The user can finely adjust the QR valley value at which the converter switches across the line/load voltage. Therefore, system efficiency can be optimized without the need to change external hardware components.

For even higher efficiencies of up to 92%, the digital-based 'XDPS21081 ZVS controller' can be used. This controller is the industry's first flyback controller that achieves high efficiency by using ZVS on the primary side and simplified circuitry and economical switches.

The FFR switching method using negative magnetization reduces the losses associated with today's goal switching type controllers without sacrificing the simplicity of constant frequency switching. In addition, it offers high design flexibility due to the ability to adjust a number of parameters. Engineers can tailor their designs to different system requirements.

When even higher efficiencies of 93% are desired, an asymmetric flyback topology is recommended. Infineon calls this topology a hybrid flyback, because the converter operates in a mixed flyback/forward mode. This hybrid topology achieves maximum conversion efficiency by using the magnetizing current to achieve ZVS with the primary half-bridge and ZCS with the synchronous rectifier switch.

When full compliance with the USB-C protocol is critical, the highly integrated USB Type-C port controller 'EZ-PD™ CCG3PA' is recommended. CCG3PA meets the latest USB Type-C and PD standards, making it suitable for use in PC power adapters, mobile chargers, car chargers, and power bank applications.

Based on Cypress’s proprietary M0S8 technology acquired by Infineon, it includes a 32-bit Arm® Cortex®-M0 processor, 64KB Flash, a comprehensive Type-C USB-PD transceiver, all termination resistors required for the Type-C port, feedback control circuitry required for voltage (VBUS) regulation, and system-level ESD protection. It is available in 24-pin QFN and 16-pin SOIC packages.


Choosing the Right USB-PD Power Switch
Infineon offers a range of high-performance power switch products that increase power efficiency. Recently, it has introduced a series of products suitable for modern charger designs at an economical price point.

The '600V CoolMOS™ PFD7 series' and '700V/800V CoolMOS™ P7 series' use advanced technologies at competitive price points to reduce switching and conduction losses. They also integrate gate-source Zener diodes to enhance ESD protection and system reliability.

The low total gate charge (Qg) and low energy storage in the MOSFET output capacitance (energy consumed per cycle (Eoss) during hard switching) increase the switching losses of the MOSFET. Reducing this total charge consumed per switching cycle improves system efficiency at light loads.

Improved technology increases device temperature coefficient by reducing device conduction losses. The RDS(on) rating of a MOSFET is for 25℃, and the junction temperature rises higher than that during operation.

Compared to the previous generation C6 technology, the PFD7/P7 series reduces conduction losses by 10% at 100°C with a 10% reduction in RDS(on). At 125°C, the industry standard is 2x the data sheet value for RDS(on), but this has recently been reduced to 1.9x.

By increasing conduction and switching losses in this way, higher RDS(on) MOSFETs can be used to reduce overall system cost, or alternatively, the overall system switching frequency can be increased to reduce form factor and lower passive component costs.

Choosing the right package can also improve the performance of your USB-PD charger solution. An example is the economical SOT-223 package. This package can be a direct replacement for DPAK at a lower price.

The ThinPAK package has very low source inductance, uses separate driver source wiring to provide clean gate signals, and uses an enhanced rectifier loop (MOSFETs, diodes, capacitors) to achieve extremely low parasitic inductance.

ThinPAK packages, which help reduce VDS overshoot, enable faster and more efficient switching of power MOSFETs and are easier to handle in terms of switching operation and EMI.

On the secondary side, the 'OptiMOS™ PD series' can be used for synchronous rectification and load switching of USB-PD chargers. This product family provides MOSFET products with low RDS(on), low switching loss, low gate charge, output charge, and low reverse recovery charge.

Additionally, logic level versions are available, allowing operation up to 4.5 V or directly with an MCU, reducing the number of components in your application. PQFN 3.3 × 3.3 and SuperSO8 packages can reduce the size of USB-PD chargers.

Meanwhile, Infineon offers a readily available '65W 20W/in3 (50CC) USB-PD Digital FQR XDPS21081 Reference Design'. This silicon-based solution features robustness, high power density, low cost, and ease of design. It reduces production complexity by using standardized components.


Infineon offers comprehensive solutions for USB-PD
The USB-PD protocol is unifying the charger market. Infineon offers a comprehensive portfolio of cost-effective solutions for high-density USB-PD charger designs. A wide range of power MOSFETs, controllers, and reference designs make it easy for design engineers to select the right product for their design.

The digital-based 'XDPS21081 XDP™ controller' improves the flyback converter by using a new control technique for ZVS/ZCS operation. Customized superjunction high-voltage 'CoolMOS™' and low-voltage 'OptiMOS™' product families provide cost-effective power switch solutions that can reduce end product costs.

A variety of USB-C protocol controller products enhance wired communication capabilities. Flexible reference designs allow for quick and easy development of desired USB-PD charger solutions.



This article is a summary of the article titled “Solved Problems Look Easy - USB-PD Solutions” by Tim Hu, Global Low-Power SMPS Application Director at Infineon.