I didn't see anyone bring this up, and I'm not sure which dielectrics and types are being used, and at risk of stating what is likely trivially obvious to the electronics designers in this august group <g>, but when using MLCC and going to smaller size capacitors (X5R and X7R, others) don't forget to re-check the dielectric voltage-dependence curves. For your chip film caps, this is far less an issue.
Here is some info and references, just in case some of your non-electronics designers want to check it out: Although this article is testing with higher valued caps, here's a nice graph showing how the smaller chip sizes increase this effect over larger sizes: http://www.edn.com/design/analog/4402049/2/Temperature-and-voltage-variation-of-ceramic-capacitors--or-why-your-4-7--F-capacitor-becomes-a-0-33--F-capacitor (Figure 1 and Table 2) (From the following original article:) https://www.maximintegrated.com/en/app-notes/index.mvp/id/5527 Most everyone is aware of the DC bias dielectric effects, but note that AC waveforms have some dielectric effects as well, but exert their effects in the opposite direction, to a point and are, of course, frequency dependent (I am not sure if these AC dielectric effects are also size-dependent or not, but it would be logical they might be): http://catalogs.avx.com/SurfaceMount.pdf (PDF page 128, [doc page #127]... Figures 2, 3) :-) Doug On Sun, Oct 9, 2016 at 11:18 PM, Andrew Greenberg <a...@ece.pdx.edu> wrote: > > Are there any places where we need to be concerned about wattage? > > Yep! There are two cases that we won't switch packages: one where > wattage is a problem (so far, no cases of this on the LGR board) and one > where the capacitance value is too high for an 0402 (anything greater > than about 1 uF). In these (and other cases I'm sure I missed) we'll > leave the larger packages. Other than that, the "jelly bean" parts can > be switched to 0402. > > OK, everyone seems to agree it's a "go", so now OreSat's default package > size is now 0402. I think this makes sense. > > Andrew > > -- > ------------------------------------------------------- > Andrew Greenberg > > Electrical and Computer Engineering > Portland State University > http://www.ece.pdx.edu/ > a...@ece.pdx.edu C: 503.708.7711 > ------------------------------------------------------- > > _______________________________________________ > psas-avionics mailing list > psas-avionics@lists.psas.pdx.edu > http://lists.psas.pdx.edu/mailman/listinfo/psas-avionics >
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