­ USB-C Charging Solution at 42 W/inch3

Currently, USB connectivity is the most widely used standard for mobile consumer goods and that popularity will only increase in the near term. The European Union is currently working to pass laws that will mandate USB charging to almost all consumer goods in an effort to reduce waste and increase convenience for consumers. For manufacturers, that will mean that they have to increase the power and the versatility of their offerings to be able to charge as many appliances as possible. 65W chargers will not offer enough power to charge modern devices in adequate time. It will also incentivize manufacturers to standardize on USB for the rest of their products, whether they are used within the EU or not, to save on engineering cost. The introduction of GaN technology has helped those manufacturers to push the limits of technology even further and get more power into compact form factors. As each new generation of GaN products are announced, their makers are keen to show off their potential by creating designs that are more powerful and efficient. Infineon are one of those GaN manufacturers, and the company used the PCIM exhibition to demonstrate its latest GaN MOSFET technology by showcasing a flexible 240W USB-C charging design with dual outputs.

The specifications for the supply required it to accept any voltage from 90 – 264 V to cover mains supply voltages around the world. The outputs would have to self-configure depending on the requirements of the load to a maximum of 240W on one single input, or a combination of power output that would not exceed 240W combined. To design the supply, the company first had to choose a topology. Pareto analysis graphs were plotted using the company’s MOSFETs in different topologies to decide the best balance between power density and efficiency. To get the best overall system, Infineon decided to use three stages to the supply – an interleaved totem-pole input, a DC/DC transformer (DCX) and a zero voltage switching (ZVS) buck converter output.

The initial ZVS Totem-pole PFC had a fixed 400kHz switching frequency in continuous conduction mode (CCM), which was interleaved to give 800kHz effective frequency for the EMI filter. The stage used Infineon’s 140mΩ CoolGaN 600 V GIT Integrated Power Stage (IPS) and 48mΩ CoolMOS 600V Si-SJ MOSFET, which together gave a typical efficiency of 97.9% with at 240W, with an input voltage of 120V and an output voltage of 300V.

The second stage of the power supply was an unregulated DCX with a fixed conversion ratio of 28:5, which again used the company’s 140mΩ CoolGaN 600 V GIT in combination with its 2.5mΩ CoolGaN 100V SG. The circuit had a switching frequency of 425kHz and offered load independent ZVS in all operating points. The full-bridge and full-bridge configuration allows the circuit to start-up with a discharged output with duty-cycle modulation. The set up had a typical efficiency of 98.3% at 240W, with an input voltage of 300V and an output of 52V.

The final ZVS buck converter output stage used the same 2.5mΩ CoolGaN 100V SG MOSFET. The circuit was designed to offer zero voltage switching in all operating points and had a variable operating frequency of between 120 kHz and 420 kHz. It provided a typical efficiency of 99.3% at 240W with 55V input and 48V output.

Together the three stages combined to provide a 240 W USB-C charger power density of 42 W/inch³ uncased or 24 W/inch³ in a case at a total conversion efficiency of 95.3%. Infineon will continue to develop its solutions for USB-C charging, initially by combining the components in the secondary transformer side into a half-bridge multi-chip module (MCM) in a 6x9 mm laminate, thermally optimized package which includes 2 x 2.5 mΩ 100 V CoolGaN HEMTs in half-bridge configuration, a GaN-optimized half-bridge gate driver with regulated bootstrapping supply, and all the necessary high-frequency capacitors.

Infineon currently has no current plans to sell the USB charger kit, which was developed for demonstration purposes only.

www.infineon.com