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I need to select a 300uF capacitor and it is mentioned in the datasheet that it should be a Low ESR capacitor. However, it is not mentioned the impedance range or how much it should be.

How can I know if the impedance value is low or high ? If I find a capacitor with 0.5 ohm impedance at 100kHz, is it Low or High ?!

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    \$\begingroup\$ link to the datasheet, we can't guess the context \$\endgroup\$ – Neil_UK Aug 4 '16 at 8:13
  • \$\begingroup\$ depends on your application. pls share the ref. docs \$\endgroup\$ – User323693 Aug 4 '16 at 8:14
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In general, the impedance of a capacitor with an ESR can be computed as \begin{equation} \dot{Z}_c = ESR - i\frac{1}{\omega C}.\end{equation} Then, knowing the frequency at which the total impedance is given (f = 100 kHz), just solve the equation for ESR.

Usually, values of ESR higher than 0.1 ohm are considered to be "high", but of course that greatly depends on your application.

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    \$\begingroup\$ What constitutes low/high ESR may also depend on the composition of the capacitor, and the expectations that are associated with it. A "low ESR" electrolytic capacitor may have an ESR that would be considered quite high for a ceramic capacitor. \$\endgroup\$ – duskwuff -inactive- Aug 13 '16 at 17:45

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