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I'm looking at a capacitor that will be used as an output cap on a buck regulator. Looking at what I think is the same exact cap from TDK (10uF, 16V, X5R) but in an 0603 and an 0805 package.

Beyond those parameters, is there something else I should be paying attention to that's likely to change as package sizes change? I can't find ESR or ESL values in either, other than a nominal "low ESx" statement in the description.

In general, what starts to give as package sizes decrease for capacitors?

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What gives? Cost, availability are non-technical factors. The smaller ones cost about triple the price in 1000's. You can check and see what other sources you have available if the TDK ones are not in stock.

The voltage coefficient also tends to be higher for smaller parts, meaning you'll typically see less capacitance at operating voltage for the smaller part.

Edit: You'll have to dig pretty deep to find the voltage coefficient specifications, on the manufacturer's websites. Here's some representative performance of similar Japanese-made parts (Murata), thanks to a Maxim article.

http://www.maximintegrated.com/en/app-notes/index.mvp/id/5527

Edit2: I really suggest you go to http://www2.tdk.co.jp/ccv/step3.asp. It's an online tool that will show you the typical characteristics of a TDK component directly from the part number. Most of the characteristics of the smaller part are worse including tempco and voltage coefficient (the 0603 almost does a disappearing act at 10V bias).

enter image description here enter image description here

For what it's worth, I went through this selection process a few weeks ago and chose 0805 parts for two new products.

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  • \$\begingroup\$ What's the voltage coefficient? I don't see this listed on the Digikey description. \$\endgroup\$ – kolosy Aug 19 '14 at 20:11
  • \$\begingroup\$ @kolosy You are going to need to look at the datasheets. Digikey can't list everything related to the capacitor in their product tables. Always look at the datasheet of a product before buying it \$\endgroup\$ – Funkyguy Aug 19 '14 at 20:19
  • \$\begingroup\$ See edit- voltage coefficient means your '10uF' capacitor probably will be more like 5uF under operating conditions. A pretty good high-capacitance varactor. \$\endgroup\$ – Spehro Pefhany Aug 19 '14 at 20:24

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