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'[OT] separating analog and digital power supplies,'
1999\08\08@230256 by Dennis Plunkett

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At 09:54 2/08/99 +0530, you wrote:
>Hi Gennette,
>
>Good idea. Does it really cost you 30 cents + 60 cents for 3 diodes and
one cap
>? Here in India, it costs only 1 cent for 1N4007 and 9 cents for 470 uF /
25V of
{Quote hidden}

People,
I don't agree with this soultion. In general it only partly covers up the
problem nad is very dependant on the type of three terminal regulator used,
as some will not present large amounts of quiesent current into the ground
pins where others will. Also the dynamic response will create problems that
will induce noise into the analaogue supply by produceing effective ground
bounce as the digital rail is moved around. Also the diode will not be
matched and variances in supplies will occur. This may provide some
problems with low power circuits as one attempts to find the elusive
missing microamps.

So what is my solution?
This depends on the application.
In general there is no reason why the same regulator can not be used to
drive both the digital and analogue supplies as long as the gounds are
seperate and don't transvers the PCB in a // method, and the same for the
supplies. Bring back both the analogue supplies to the regulator and use
MECCA or STAR type single point grounds, inducotr can be used in the supply
line if you require, but should be avoided in the digital supply i.e. Can
be used in the analogue supply.


Dennis

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