Parallel caps in schematics

Jon Slaughter · 2007-08-02T14:00:19+00:00

How come in some schematics I see many parallel caps? Why don't they combine them into one?For example, in a TI ADC EVM(ADS5444) schematic it has 3 parts that say "Bypass caps for DRVX" where X goes from 1 to 3 and all are identical. Each one uses 3 different types of caps all in parallel.1x10uF 10V (polar)3x0.1uF 16V3x470pF 50VI assume that this is simply to get the required capacitance in terms of standard values?If my calculations are correct then the 6 parallel non-polar caps should have an equivilent capacitance of about 0.3uF.Now this brings up an issue. The 3 pF caps do not really add much capacitance so what are they for? They are rated at 50V but surely at 10V the first cap will go(theoretically) making the others useless? (although maybe they exist for transient reasons?)Any ideas?Thanks,Jon

Aug 02, 2007 42 Replies

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JosephKK 18 years ago

DJ Delorie snipped-for-privacy@delorie.com posted to sci.electronics.design:

In the case of Johnson's "Black Magic" it was always wrong. See the post from John. BTW I despise the title as well.

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John Larkin 18 years ago

Sadly, half of what he writes is good stuff and half is nonsense. If you can tell which is which, then obviously you don't need him.

John

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JosephKK 18 years ago

John Larkin snipped-for-privacy@highNOTlandTHIStechnologyPART.com posted to sci.electronics.design:

I really doubt that so much a half of what is spouted is useful.

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