Electronics > Beginners

BOM prob. ESR Output Capacitor - TPS5560200

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MagicSmoker:
I'm inclined to side with CJay here, but to answer the OP's question, anyway... ESR is the lumped sum of the actual ohmic resistance of the conductors, plates, etc, and the equivalent resistance from dielectric losses; it's not a type of capacitor, it's a property of them. Sometimes the cap manufacture gives the ESR, but sometimes they are a bit more sneaky and give a spec for "dissipation factor" (either in percent or the tangent of the loss angle). In either case, D.F. is the ratio of ESR over capacitive reactance and is heavily influenced by the type of dielectric, clocking in around 0.1-0.2% for both NP0/C0G ceramic and polypropylene film types, 2% for polyester/PET types, and 3% for Hi-K ceramic types (X7R, Y5U, etc.)

So for example, a 1uF NP0 MLCC with a D.F. of 0.15% will have a capacitive reactance at 100kHz of 1.59 ohms and an ESR of 2.39 milliohms, but if the dielectric is X7R then the ESR will jump to 47.8 milliohms.

Since ESR behaves exactly like a resistor it leads to heating of the capacitor and produces ripple when fed with alternating or pulsating current (like the output of a switchmode converter), hence two good reasons to minimize it right there.

ESR isn't always bad, however, but why that is the case I leave it to those interested to search for themselves.

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