Supercap speed question

Thread Starter

Janis59

Joined Aug 21, 2017
968
Hi! Here is one application having need for extra good ripple push-down, thus the 1 Farad 5 Volt capacitor may stand for be ideal solution inspite even the price. But the circuit using this power Vcc will have a 8 MHz clk, and power supply givig this Vcc have the ripple 0,5 MHz; thus the cap must be fast enough even if surrounded with plentitude of ceramic paralleling caps.

Thus, I overlooked some dozen datasheets of different firms of supercaps - NO ANY word about speed, max frequency as only warranted ESR at 50 Hz and at 1000 Hz.

May someone advice me something to read about their habits at far higher frequencies??
 

Chris65536

Joined Nov 11, 2019
154
Supercaps are not just high value electrolytics. They have characteristics of batteries as well. In any case, there is some info on frequency dependence in the Wikipedia article. https://en.wikipedia.org/wiki/Supercapacitor#Electrical_parameters
There is a graph on there which shows at only 1Hz, the supercap is already de-rated to 60% of its nominal capacitance. At 10 Hz, it's below 20%, and at 100Hz maybe 3%. This looks totally unsuitable for high frequencies.
 

Analog Ground

Joined Apr 24, 2019
271
AVX makes a series of supercaps characterized for pulse applications. The behavior over time during a pulse load is characterized in the technical papers at this link. Not capacitance vs frequency info but at least something. In the data sheet for these devices, the ESR is spec'ed at 1000 Hz. Anyway, if I was looking for fast response, I would check these out.

http://www.avx.com/resources/technical-info-papers/technical-papers/pulse-supercapacitors/
 
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