[SI-LIST] Re: basic question regarding inductor before Vcc
- From: steve weir <weirsi@xxxxxxxxxx>
- To: Vijay S CHACHRA <vijay.chachra@xxxxxx>, roymesi@xxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Mon, 20 Jun 2005 03:13:44 -0700
Vijay, just do a Google search on power supply filters, and damping.
Steve
At 01:31 PM 6/20/2005 +0530, Vijay S CHACHRA wrote:
>Steve,
> Can you pls point to a suitable literature (in pdf files or
>url links) to understand the calculations and how to reach
>at appropriate values of 'L' and 'C' elements in bypassing
>network?
>
>Thanks and Regards,
>Vijay.C
>
>---- Original message ----
> >Date: Fri, 17 Jun 2005 11:37:33 -0700
> >From: steve weir <weirsi@xxxxxxxxxx>
> >Subject: [SI-LIST] Re: basic question regarding inductor
>before Vcc
> >To: roymesi@xxxxxxxxx, <si-list@xxxxxxxxxxxxx>
> >
> >Roy, sure a series impedance decouples the IC from the
>surrounding
> >interconnect. Done properly, that can be a good thing for
>issues such as
> >EMI. When a thirsty IC inhales lots of current that wave
>propagates trough
> >the interconnect until it either dissipates due to
>resistive, and radiated
> >losses, or encounters an impedance discontinuity such as a
>decoupling
> >inductor. That works two ways and can isolate digital
>return currents from
> >traversing a sensitive analog path in an IC such as are
>used for PLLs.
> >
> >The bad news is that many people design bypass / decoupling
>networks by
> >rote rules and happenstance. An inductor that isolates an
>IC that is not
> >matched with enough capacitance to supply the IC is a bad
> >thing. Similarly, a combined inductor and capacitor
>network can peak badly
> >making power quality much worse than without the inductor
>in the first place.
> >
> >Steve.
> >At 07:59 PM 6/17/2005 +0200, Roy M. wrote:
> >>Hi,
> >>can someone explain to me why the board designers put
>inductors just
> >>before the Vcc connection? is it some kind of filter
>against noises?
> >>I understand that when you put a resistor, it is intended
>for lowering the
> >>voltage or for pull-downs... but what's the logical
>explanation for
> >>putting an inductor?
> >>Thanks,
> >>Roy
> >>
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