Using LLC resonant controller to speed up device operation

To be the best, people go to incredible lengths. For example, athletes train tirelessly to beat the competition by a millisecond. Students spend years studying to achieve top academic achievement. Companies or organizations spend decades researching new technologies to solve problems that once only existed in science fiction. And finally—the tech-savvy—power engineers work to develop superbly efficient, high-density converters.

I bet that when most of you fired up your circuits, you achieved at least your personal best in terms of power density and efficiency. You went home and probably enthusiastically described your exciting experience to your spouse or children, only to have them bewildered by your actions.

Rest assured, you won’t get that kind of feedback here. Personally, I like to explore new things and try to make them better than before. TI has a new controller, the UCC256301, that is currently making a lot of noise because it makes power supplies perform really well.

The UCC256301 is the latest in the TI LLC controller family, as shown in Figure 1. Its features and benefits include integrated high-voltage startup, x-cap discharge, robust fault protection, and a new, absolutely reliable control method.

Figure 1: UCC256301 system block diagram

During the competitive product analysis, UCC256301 outperformed similar devices in terms of stability margin, ease of design, powerful protection mechanism, light load efficiency and transient interference suppression.

Now, let's take a look at the following example. I modified a commercial gaming system using the UCC256301. Figure 2 shows the load transient response before and after the modification.

Figure 2: Transient response improvement

The stock board actually performs quite well. However, look at what the UCC256301 does on that! Load transient response becomes less important. For the manufacturer, this could mean a 20% reduction in output capacitance, not to mention other component savings in enhanced performance and integration. The block diagram in Figure 3 illustrates the savings with a different system-level circuit like this device.

Figure 3: System-level component savings

In the same gaming system, I achieved additional performance improvements in output ripple voltage in burst mode (Figure 4, 10x smaller) and light load efficiency (Figure 5, 10% better efficiency). In another system, I measured less than 40mW of no-load power while fully regulating the output even in the presence of a high voltage power factor correction (PFC) input. To me, this exemplifies the concept of an accelerated device. I tried to tell my wife and kids about this, but they gave me blank looks in return.

Figure 4: Ripple Lift

Figure 5: Efficiency improvement

There are many more aspects of this device that could be discussed; however, at its core is a new control architecture called Hybrid Hysteretic Control (HHC). This control architecture combines the advantages of direct frequency control LLC and charge control LLC to achieve a product that is superior to the others. In fact, this control method goes a long way to improving performance.