I was thinking one reason to use the tantalum was because it could pack more capacitance in a smaller space.
I was thinking one reason to use the tantalum was because it could pack more capacitance in a smaller space.
I suspect you need to see a diagram of the circuit because you are thinking of a resistor directly in series with the capacitor whereas Joe and John were thinking of placing the capacitor directly across the load (chip) and a resistor between the regulator and the supply pin of the load (chip), (with its capacitor).
The ESR would be high if measured from the location of the regulator, because there would be a resistor between the regulator and the capacitor. The ESR would appear low if measured from the location of the chip which is the load (chip), because the capacitor is directly in parallel with the load (chip). The disadvantage of this arrangement is that the average (DC) load current flows through the resistor which might cause an annoying reduction in the supply voltage at the load.
Nevermind, others have already said what I tried to say.
One other option is Niobium Oxide caps, sold under the brand oxi-caps. Digi-Key has them. I have used several thousand of them on some gear that some users run in hard vacuum, so aluminum electrolytics were out of the question. I have mis-connected a few of the oxi-caps, and can verify they will char a bit, but not burst into flame.
Jon
You can get MLCC capacitors as big as 180uF - but it won't fit in the original space.
They're mostly advertised as SMD, but that certainly won't fit - a few suppliers offer resin dipped leaded versions that you could form the leads to meet the pads.
Aluminium electrolytics of any kind are a no no! - there was much chatter about organic semiconductor electrolytics a decade or so ago, that were claimed to be as good as tantalum, but it lately seems to have gone very quiet on that front.
Tantalum electrolytics are *VERY* intolerant of reverse voltage, even just a little bit makes them go leaky. When the normal supply comes back - if it can shift much current; the tantalum goes off like a match head!
The polymer aluminums are really good. Low leakage, low ESR, don't dry out.
Saw an article about those a while ago - did they ever take off?
The organic semiconductor variety were supposed to be the "dog's nuts" - but all the hoo ha seemed to mysteriously fade away.
Do they exist in the upper mF range (4700+uF) for, say, 35V?
Best regards, Piotr
Check the distribs, but I think not. The CV products seem low, like
4700 at 2.5v. Don't know why.
Well, in LV SMPSes you really really care about ESR.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant
I've had excellent results using two 22uF aluminum electrolytics, one on the input, one on the output, of ZLDO1117 regulators. I've built several hundred devices with that setup, to produce 1.2 to 3.3 V supplies for FPGAs.
Jon
I believe he set up the production line to ramp up the supply voltage with current limiting on EVERY board as it comes out of the reflow oven.
Jon
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.