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| 5V-to-3V3 LDO compatible with 0 ESR output cap? |
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| rs20:
Hi, I realise these requirements are somewhat conflicting, but I didn't expect them to be conflicting to the extent that I've had difficulty finding a singling matching candidate. So I'm looking for: * A linear voltage regulator, taking: * Input voltage: 5V to 12V * Output voltage: 3V3 (so, a max dropout of 1.7V then I guess, which is where the trouble starts) * Stable with ceramic output capacitors (i.e., basically 0 \$\Omega\$ ESR, if only I could use a non-LDO regulator) * Output current: > 500 mA (not a hard requirement) * Through-hole package (not a hard requirement) Could anyone please suggest matching parts? I've looked through a dozen parts on digikey, and setting the parametric search of requirements #1-#3 seems to only yield parts failing to meet #4. And as something of a meta-query, what's the best place to do parametric searches where you can specify the 0 ESR output capacitor condition? To preempt the often reasonable response, "It's much easier to find a 1 \$\Omega\$ ESR cap than an LDO matching these requirements"; the application here is for a parts bin in a shared space for random fooling around. IMHO, that usecase calls for an idiotproof part, and in 2019 idiotproof means compatible with perfect capacitors. Also, I've never understood why it could be OK to have a tantalum/electrolytic cap at the output of the regulator, but then having a dozen 1uF ceramic MLCCs on the same net as input caps to various ICs downstream. Am I supposed to be relying on a certain level of ESR/loop inductance in my power distribution traces to prevent those other caps from bringing the LDO into instability?? Anyway, I'm drifting off topic... |
| kony:
Polymer cap and series resistor is a viable path as well sometimes, even the most cost effective and long device life choice as well. |
| Deepak:
So an LDO relies on the ESR of the cap for its feedback system therefore you won't find any such chip through a parametric search. If you must have a 0 ESR cap then you could get away with adding a resistor at the output of the LDO, but it would need to be small value and within tolerance over a wide temp range. And there's no such thing as idiot-proof... |
| rs20:
Thanks for the suggestions of using a separate ESR resistor (although I'm puzzled by the "within tolerance over a wide temp range" bit; absolutely any half decent 1 ohm resistor can stay within 0.1 to 2 ohms over temperature??), however such external solutions don't meet my "idiotproof" requirement. --- Quote from: Deepak on March 15, 2019, 01:11:28 am ---So an LDO relies on the ESR of the cap for its feedback system therefore you won't find any such chip through a parametric search. --- End quote --- Counterexample: MIC5203-3.3. It is an LDO (0.3V dropout) and specifies no minimum ESR. So although it's SMD and only supports 80mA output; I think it's not reasonable to conclude that the design couldn't be stretched to a through-hole 500mA part. The question remains whether such a part is available from distributors though. |
| DaJMasta:
There are quite a number of LDOs that specify ceramics as their output capacitor, not sure about a "0 ESR" specification, but at least expecting very low. It could be that most of them are designed for lower operating currents, though, meant for boards with a slim profile or local regulation that doesn't require all that much current. |
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