If you haven’t yet heard the news, National Semiconductor has added six high-frequency buck regulators to its SIMPLE SWITCHER product family. In addition, they have added a “dial” to their online WEBBENCH design tool. Why the dial? All of the new regulators have an adjustable switching frequency, and the dial gives you an easy way to change parameters that are dependent on the frequency, such as size and efficiency. National thinks that novice as well as seasoned power supply designers will benefit from the new tool.

National is also making evaluation boards available. In fact, there was one in the press kit they gave me—an LM25576. As described in the press kit, the LM25576 demonstration board is a fully assembled and tested platform to evaluate the LM25576 SIMPLE SWITCHER step-down converter. The demonstration board takes a 6V to 42V input and generates a regulated 5V output that can source up to 3A of current.

I had no idea if the board in the press kit was a working model or not, so I put it to the test. I dug a 12 VDC wall adapter out of my pile of adapters, plugged it into an outlet and measured the output on my multimeter--20.89 VDC. I don’t know about you, but I was surprised at the 75% error in the voltage rating. Since the board can handle this voltage, I connected it to input, and then measured the output--4.99 VDC. Good job, National!

I’m sure that there’s more to test if you actually want to use the eval board in a circuit, but that wasn’t the case here. Instead, I wanted to take the next step and try out WEBBENCH. I went on to National’s site (www.national.com) and registered so that I could use WEBBENCH.

I decided to design a supply that is similar to the eval board that I have, except with a 3.3 VDC output. So I filled in Vin = 6V Min, 42V Max, Vout=3.3V, Iout=2A. When I clicked on Start Your Design, the recommended device was none other than the LM25576, which was fine with me. I accepted the recommendation, and a page appeared with the dial on it as shown in the FIGURE. I figured that I would increase efficiency from 75%, so I moved the dial from 3 to 4 (the dial has only five positions). This increased efficiency to 77%, but also increased the footprint from 305.6 mm² to 365.8 mm² . Moving the dial to 5 increased the efficiency to 81% but increased the footprint to a whopping 885.2 mm². I decided to stay with number 4 and also accepted all the parts that WEBBENCH recommended for the board.

From this point, I went ahead and did a thermal simulation and then an electrical one. The board that the tool created passed the thermal inspection and also seemed to do well on the electrical simulation, as far as I could tell.

Now it was time to order a board. When I clicked on Build It!, I got four choices: 1) Buy an unassembled custom kit for $63.06 plus $16.50 shipping plus tax; 2) buy just the IC; 3) order a free sample; and 4) order a generic demo board that would not be customized for my design. The demo board costs $37.50 and is, in fact, the board that I have. I considered the unassembled custom kit, but since I don’t have a pressing need for it, decided against it. My design, though, was saved automatically by WEBBENCH and will be ready to go as soon as I figure out a good application for it.