Tear Down: Spigen PowerArc ArcStation Pro GaN-based Charger
January 31, 2023
The last Tear Down I did, the Meta Quest 2 VR headset, got lots of fanfare. As an end product, it’s super cool. And from a design perspective, I was awed by what the engineering team was able to accomplish.
While less glitzy, this next Tear Down, of the Spigen 20-W PowerArc ArcStation Pro charger, is just as important. The charger is based on Gallium Nitride (GaN) technology, which is a big step forward from previous silicon-based chargers. The model that I took apart was based on a European adapter. I picked it up when in Germany, so I got to use it briefly and did realize the stated feature set. But once I got back to the U.S., it was time to dissect it.
For an application that seemingly is quite simple, there were lots of ICs on each side of the pc board. The key component, and the one that is a difference maker in this application, is the Navitas NV6113 power IC. It’s part of the company’s GaNFast family that is optimized for high frequency, soft-switching topologies.
The 5- by 6-mm power IC, which functions as the main primary side switching device on the transformer/charger, integrates an FET and other logic to create what the company calls “an easy-to-use digital-in, power-out high-performance powertrain building block.
“The result is a charger that outputs 20 W in a package that’s much cooler and about 30% smaller than silicon alternatives,” says Steve Oliver, a Vice President at Navitas. “And it can operate about three times faster thanks to its high dV/dt immunity, which represents the rate of voltage change over time, a metric common to MOSFETs. A typical modern smart phone would charge about four times faster using a GaN-based charger like the PowerArc.”
Moving From Si To GaN
Moving from older silicon technology to GaN, a slight redesign (upgrade) is required to take advantage of the high speed switching. A higher frequency device would need to be sourced, and that’s what occurred here. On the Spigen PowerArc ArcStation charger, the high-frequency quasi−resonant flyback is an onsemi NCP1342. While allowing the charger to run at the higher speed, the part also shrinks the size, cost, and weight of the transformer that's employed. The cost reduction results partly from the use of smaller output capacitors. In addition, the cost and size of the EMI filter can be reduced.
As a refresher, switching speed refers to the rate at which you put energy into the transformer and then take it out. The faster you can do that, the smaller the transformer that’s needed, as less energy is stored at any given time. If you switch too slowly, the transformer would go into saturation mode and essentially shut down. The PowerArc ArcStation runs at around 250 kHz, which is about five times faster than a silicon-based charger. In terms of size, the PowerArc, the transformer is down to about 8.5 mm, where it’s typically more than 20 mm.
The NCP1342 features a proprietary valley−lockout circuitry, ensuring stable valley switching. In operation, as the load decreases, the NCP1342 enters a quiet-skip mode to manage the power delivery while minimizing acoustic noise. And for high-frequency designs like the PowerArc ArcStation, the NCP1342 incorporates rapid-frequency foldback with minimum peak current modulation to quickly reduce the switching frequency. Over-voltage protection is also designed into the NCP1342.