So, the BOM calls for 560pf’s, well, I don’t have any… so will running a 100pF and a 470pF be fine?
And will it work the way I have it?
Since the board is dense, the paralleled caps are on the other side…
Hence me asking this. Lol
Since the board is dense, the paralleled caps are on the other side…
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Yes, that’ll work.
You may find this calculator useful for things like this:
https://files.northcoastsynthesis.com/spcalc/
(it points out 470pF + 100 pF is a 1.8% error, which isn’t much compared to the tolerance of a typical ceramic cap – even a 470 pF on its own might be ok here.)
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Peeked at the schematics and these 560 pF caps are used in the filter core. The specific Murata component listed in the BOM has the following specs:
| TYPE | DESCRIPTION | |
|---|---|---|
| Capacitance | 560pF | |
| Tolerance | ±5% | |
| Voltage - Rated | 25V | |
| Temperature Coefficient | C0G, NP0 |
The ±5% tolerance corresponds to roughly ±30 pF so you’re within spec. C0G is a class 1 dielectric with zero temperature drift, which definitely is nice but not necessarily a must have. You can always swap them out later.
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Thank you so much fredrik!!!
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Should perhaps point out that “within spec” assumes that your caps are reasonably close to their nominal value. If they’re both eg 20% too low, overshooting by 1.8% won’t improve much . And since this is a multipole filter, you want the caps to be close to each other, otherwise the filter response won’t be as good as it can be. But build it and see if you like the result. As I said, you can always replace them later.
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woah. thanks for this link! so helpful.
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