I am building a power supply circuit, and the switching regulator (L4963) calls for a low-ESR output capacitor. The capacitor in question is C3 of the evaluation board circuit.
What does "low" mean? How low?
Also, how do I find or calculate the ESR for a capacitor whose datasheet does not have a parameter called ESR?
Best Answer
If a datasheet just says 'low ESR' without specifying a value, you are usually fine with any style of capacitor with a relatively low ESR. All this really means that you should avoid cheap unrated aluminum electrolytic capacitors, since their ESR is terribly high and can be several ohms.
In this case it wants a 'low-ESR' capacitor for the 1000 µF output capacitor. I don't think I've ever seen a ceramic 1000 µF capacitor and a 1000 µF tantalum capacitorwould probably cost US$50, so you are going to have to track down a low-ESR aluminum capacitor for this application. The output ripple will decrease linearly with the ESR of the capacitor, so lower is better up to whatever price you want to pay.
As an aside, that is a ridiculously high required output capacitance for a switching regulator in that voltage range. You may want to take a look around for a regulator that meets your needs, but is stable without such a requirement. Don't get me wrong, usually the more capacitance the better, but 1000 µf is really high for a 1.5 A power supply.