I've had the opportunity to lay my hands on power management devices classified as “digital controllers.” The opportunity came when I worked at Intersil. I regularly get press releases touting new digital controllers. My reaction is generally, “Great, another one; so what?” I react that way because, in my experience, these devices never got much traction.
I knew they were good products — well engineered and would work as advertised. But they were a hard sell. I talked to a lot of engineers about the previous generation parts. Some of the guys with whom I spoke, I'd known for 10 years, so I knew what they knew and vice-versa. But even with that audience, the reaction was usually “Meh — nice part, but what we have now is fine. I don't want to take the time to learn to use something new.”
With this new part that I'm looking at as I write this (the ZL8800), I think someone has finally got not just the technology right, but the user interface, too. The part is a dual channel, dual phase controller. The first thing to remember is that it's a controller , intended to have external power FETs attached. So you'd use this for power supplies that were sufficiently high power that external (big) FETs were needed.
Dual channel/dual phase means that you can use this part in one of two ways. You can build either two separate switchers, as shown in Figure 1:
Or you can build a single power supply whose switching elements are operating 180° out of phase; that reduces ripple in the output voltage. That circuit is shown in Figure 2:
These are both simplified schematics of course, but the actual circuitry is not much more complex. There are no external components needed for compensation. That's taken care of via the digital control loop. The control loop produces very fast transient response and reduces the size of the output filter caps that you'd expect to need.
To design a power supply system, you use the software provided by Intersil. It has an easy to learn and use GUI that lets you drag and drop blocks representing as many supplies as you need. Then you can interconnect them and specify sequencing. You can use the same software to monitor the supplies in operation. Typical parameters that you would likely monitor are input voltage and current, output voltage and current, switching frequency, the duty cycle of the power FETs, and operating temperature.
The simplified schematics from Figures 1 and 2, above, can be compared to the actual circuitry that you can see on one of the Eval boards. It's not much more complex. There is some extra circuitry on the Eval board, but it's there to make testing easier. A production version of the circuitry would take up far less real estate than what you see represented in Figure 3.
One more important detail: For power supplies that are part of critical equipment that need to be monitored and whose performance must be logged, these parts are ideal. They contain non-volatile memory and can log their operating points. So, if something does go wrong, you can tell what caused the problem. You can also use the logged data to help predict when maintenance will be required. This is useful in hot-swappable supply modules that are part of UPS systems.
Have you used any digital power supply devices from any of the several manufacturers that offer them? How well did they perform?
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