From: sweir ([email protected])
Date: Tue Mar 07 2000 - 17:42:00 PST
If you are sadistic, they will drive your purchasing crazy, as tant's are
hard to come by these days.
The PLD edge rates need to be watched. You can optionally filter the
outputs depending on the application, with anything from 10 ohm series
resistors, to RC networks, should the edge rates pose a noise issue.
The tantalum caps will filter only up to a couple of MHz. So the question
that arises is, how much filtering do you need from at least a couple of
KHz where your power-supply regulator impedance goes up to a couple of
MHz? If you are really only running some RS-232 then the one 47 uF cap s/b
plenty. The 100nF caps will go inductive around 8-15MHz ( mounted ). So,
you will either need lots of them in parallel, or other smaller values to
cover at least up to 80MHz. You can refer to recent postings on this
thread for more details.
At 06:20 PM 3/7/00 +0000, you wrote:
>I have been asked to sprinkle 6.8 uF tantalum or electrolytic capacitors
>evenly around the PC board of a new design.
>As usual, I have the 0.1 uF 805 ceramics at the power pins of chips and a
>bulk storage cap. of 47 uF where power enters. The board is 3x4 inches, has
>a few chips, slow edge rates. Mainly RS-232 (up to 1 mb/s) and the
>internals of a PLD clocked at 16 MHz.
>Can anyone tell me what the benefit of these 6.8 tantalums sprinkled around
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