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Re: [N8VEM-S100:5182] Tantalum capacitor replacement?

On Sep 9, 2014, at 4:50 PM, Vince Mulhollon <vincemu...@gmail.com> wrote:

> On Tuesday, September 9, 2014 2:15:22 PM UTC-5, Don Caprio wrote:

> LDOs are a difficult beast not as agonizing as switching designs but not as easy as simple linears.  TI has a nice app note AN-1148 about LDO ESRs.  I just finished reading it and its interesting that some LDO regs but not all will break out in oscillation if the output has an ESR BELOW or above a certain ESR and it reminded me of the rule of thumb that about an ohm of ESR is about right for a LDO.  LDOs do make great oscillators, like a super high power tunnel diode.  And as the AN mentions, TI does make special secret sauce chips that have much better tolerance than most LDOs to unusual ESRs, etc etc.  Well, it is a TI app note, they're not going to compliment ON or Vishay for obvious reasons.

I just wrote a few paragraphs about this before I saw this part.  Oops.  In any case, there ARE LDOs that can handle very low ESRs on the output (including large ceramic caps, which can give you REALLY tight regulation), but they're typically for much lower voltages and power levels than you'd need for an S100 board.

It all comes down to their loop compensation, which is frequently designed assuming at least a little ESR from the output cap; if you throw off the compensation such that the gain is above 0dB by the time you hit 90 degrees phase offset, you'll get oscillation.  No secret sauce in the ones that can work with ceramics, just application-optimized loop compensation.

> I looked at the data sheets for some of those niobium caps, 50 miliohm ESR like what is that made with solid gold lead wires?  Either thats impressive or its a typo.  Actually too low ESR to keep some LDO's happy.

They're interesting.  I've not used them in a project yet, but I might have some coming up (which are already going to be expensive, so they're not going to make a difference) that might make a good pilot.


- Dave