power supply decoupling

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Hi, I saw a power supply decoupling network as shown in the attached figure. Why is this a pi network? Why not just use a tantalum cap and a series inductor?
Appreciate any help.

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You wouldn't want a tuned circuit would you?
You have plenty of capacitance on both ends to keep the circuit well damped.

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yes but why is one of the caps uF and the other pF?

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the larger caps tend to be slow to react to high frequency signals. The small caps are good for filtering the high frequency/low energy noise.

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

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The inductor serves to choke the high current transients. An inductor in series with the load will "normalize" fast currents, and the cap in parallel with the load will filter off the high frequency that still passes through the inductor. All together this keeps current and voltage regulated. This is commonly used in power supply designs at higher currents where load regulation is important, and where a RC low pass filter just would dissipate too much heat. Usually you will see this at the output of a full wave rectifier, with larger caps before the inductor to filter off most of the low frequency noise, then into the inductor, which essentially regulates current, and smaller caps on the output to filter off remaining high frequency noise.

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ok that helps a lot,thanks. We have this circuit on one of our boards and I was just trying to understand why there were so many components for decoupling a 5V supply. Any ideas/guidelines on how I can calculate the component values assuming 5V supply?

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http://www.designers-guide.org/D...
Goes as deep as you want.

Just a noob in this crazy world trying to get some electrons to obey me.

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wow that's really helpful.. thanks a ton for digging it out!

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