Eval board

Most of the evaluation boards of such ESR-sensitive parts are shipped out to customers with only aluminum electrolytic or tantalum capacitors at their outputs. But what really happens is that the customer happily connects the eval board (rather expectantly) into his or her system, and completely forgets there are a bunch of ceramic capacitors all over the system board (for local decoupling at different points). In effect, the switcher can lose that valuable zero in its control loop and break into oscillations (see Figure 3-5). More so if the connecting leads are short. 

So do we make eval boards or demo boards I still don t know the answer to that But I can tell you some of the things I personally do that make for easy troubleshooting. The way I do it, by concealing some invisible options, most boards I build can go straight to the customer. He or she will never know the difference ... 

That is how most of my board designs can go straight to the customer, and also be used fully for a normal Apps evaluation. The perennial question Is it an eval board or a demo board has been virtually sidestepped. 

Once, while working as an Apps engineer at this maker of high-voltage Flyback monolithic switcher ICs, I happened to express concern about the way they were selecting the input bulk capacitors for their evaluation boards. To this day, in my opinion, they are making several misleading/erroneous recommendations to their customers via their eval boards. 

Note that these cost a couple of hundred dollars a piece usually and are mountable on standard PCB eval boards. They are actually much cheaper than the near-permanent leadless sockets some test engineers use on special boards. 

Considering that the layout was considered so important (and rightly so), the datasheet still carries no pictures of a PCB layout. There also seems to be no accompanying App Note with that vital information. Though there is an eval board available from the company s website that you have to cough up 30 for. Short of wanting to buy it just to confirm the layout, their web site left me a little confused, but my initial impression was that the 2621 eval board features only the Sepic topology (not what this customer wanted, i.e., a Boost). 

You need to find out if they have any tricks to get around the problem. Looking at the App Note for the 5034 Eval board, the author is the guy who knows the answer to your question. 

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