[SI-LIST] Re: Experience with Power supply collapse on boards due to excessive decoupling.
- From: John Vavourakis <jvavourakis@xxxxxxxxxxxxxxx>
- To: Vipul Badoni <Vipul.Badoni@xxxxxxxxxxx>
- Date: Wed, 26 Nov 2008 01:55:08 +0200
Hi Vipul,
There is much information missing regarding your set-up/tests, like:
- is your board hosted in a PC or any other std (VXI, PXI, VME etc)
platform?
- if standalone, are you using a commercial power supply or a custom one? In
a standalone set-up, check the connections/wires from the power supply
to your
board, their impedance could be your only problem.
- in both cases, is the PSU rated for your needs?
- do you have an additional power supply module (step-up, step-down,
etc) on
your board;does it have an inrush current limiter?
- does the power supply collapse immediately when you connect your board
or after you enable some of its functional blocks? When you say
"collapse" does
it drop/swing its output going "slowly" down to ~0 mV or does it go
immediately?
- have you tried more than one boards to see if you get the same results?
- have you tried an alternative PSU to see if you get the same results?
-.......
-.......
- is there any special reason why you think that the problem comes from the
decoupling capacitors?
In general, I have used more capacitance than you are using without any
problem.
Furthermore, I usually use "bulk" capacitors say 16uF or so, nearby
"large switch
current loads" (i.e. CPUs/MCUs, FPGAs, Memory Banks etc). Maybe you
could try
this as a 1st workaround.
Cheers,
John
Vipul Badoni wrote:
> Hello SI-Folks,
>
>
> I was wondering if some of you could share with me your experiences with
> power supply collapse due to excessive decoupling of only a few values
> of capacitor on boards drawing a lot of switching current. The situation
> I am dealing with has ~400 in number of 0.1uF caps and ~200 in number of
> 1uf caps. The power supply shows a lot of noise ~400mV.
>
>
>
> Regards,
>
> Vipul Badoni.
>
>
>
>
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