Any problems with using X5R/X7R caps as buck converter output capacitors?

Let me try to rephrase this a little: Choosing the ESR of the electrolytic capacitor is still important in the case where its capacitance (C2) is significantly larger than the total of all those 100nF (or whatever) ceramics sprinkled around the board (C1) (assuming assuming the switcher's loop gain starts falling before you hit the zero of the electrolytic at ESR*C2, which I would think can be taken as a given)... right?

Thanks,

---Joel

But: Nobody is going to notify you when the manufacturer improves the caps. Suddenly their ESR becomes a lot lower, the regulator chip gets all choked up ... phssst .. BANG. IMHO relying on a cap ESR is the same as relying on prop delays. In a production environment it's like playing with fire. Hence no LDOs in this here lab :-)

OR, use a very low ESR electrolytic, in series with a resistor.

the other reason using electrolytic ESR for damping/loop compensation isnt so crash hot is its behaviour at low temperatures - expect a

Cheers Terry

It's over in ABSE now. It is an "all in one" switcher (LTC3404) .

I looked at it again today before dumping the schematic/PCB into a PDF and it's actually not as bad as I had previously recalled, but right around 3V input there's jitter around 15% of the switching period

---Joel

Hasn't shown up yet but I'll keep looking. Might be the weekend though. Got a job to finish tomorrow. Plus my missus wants a new commode in the master bath. Rear-outlet plumbing and all those nasties. Oh what fun!

Sure, understood -- I'm happy you're willing to take a look in the first place.

Would one of those Home Depot "How to do Anything to your Home" books for Xmas be received well if you got her a copy? ;-)

---Joel

It works well. But you have to look after 2 things:

- the regulator loop may require extra compensation

- the ceramic capacitor's capacitance varies by the voltage applied to it. Read the specs of the capacitor you want to use carefully.

I did, and commented over on a.b.s.e. since that's where the images are.

She's quite versed when it comes to repairs. But plumbing jobs with heavy duty lifting or anything high on a ladder fall into my job description. Got the old wall-hung commode out, whew. Behind it I found a totally weird mount. Of course. And you can't get a hand behind the bracket because they closed off the wall after mounting it. Of course. Stuff like this obviously isn't meant to be easy.

Xmas

Of course. Plumbers earn their money. IMO the only way to do plumbing is by starting with a chain saw and finish up the delicate work with a sawsall. Levers help too.

Xmas

Just finished the demo. It's scary how easy it is to crunch away drywall. Now I have to do the face lift, mending drywall back in. Don't like it much, I am used to the good stuff. Laying brick, mortar and such.

Xmas

But that's the nice thing about sheetrock; it's so easy to work with (against). The trick is to pull it down, rather than breaking it up too much. I cut close to the seams and use a pry bar to pull it off the wall. Mych less messy than using a hammer. THEN you take you the chain saw (Sawsall) to the plumbing.