[SI-LIST] Re: Bypassing on Passive Backplane
- From: "Salkow, Steven" <steven.salkow@xxxxxxxx>
- To: "'Joel Brown'" <joel@xxxxxxxxxx>, "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
- Date: Fri, 11 Sep 2009 18:53:13 -0600
IF THE PLUG IN CARDS HAS SUFFICIENT BYPASSING THEN WHY WOULD IT BE NEEDED ON
THE BACKPLANE?
Telecomm like ATCA today use Hot Swap circuitry to power up and down blades
gracefully. No one is making backplane with capacitors on them because these
are the least reliable component in our arsenal of components. Typically
backplanes are not considered a field replaceable item.
SHOULD POWER PLANES BE BYPASSED TO GROUND PLANES ON SOME GRID INTERVAL?
Yes and no. Capacitance is needed where it does the most good. Passive Leds
that changes only when a power rail blows up may not need capacitance. A
switching regulator that needs to supply varying loads that change slowly need
both high and low frequency capacitors that meet the ESR requirements as
published by the regulator manufacturer. There are books written on the
subject...
IF HIGH SPEED SIGNALS ARE ALWAYS SURROUNDED BY GROUND PLANES, ARE THE POWER
PLANES FREE OF SIGNAL RETURN CURRENTS?
High speed signals are not always surrounded by ground planes. A power plane
make act as a return path for transmission lines too.
Steven Salkow
Lockheed Martin
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Joel Brown
Sent: Wednesday, September 09, 2009 2:11 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Bypassing on Passive Backplane
Looking for advice, published guidelines, books, etc on PDN for passive
backplane.
In the past I was told to always bypass both sides of power connectors with
bulk and high frequency capacitors to prevent AC currents flowing through
the connector.
If the plug in cards have sufficient bypassing then why would it be needed
on the backplane?
Should power planes be bypassed to ground planes on some grid interval?
If high speed signals are always surrounded by ground planes, are the power
planes free of signal return currents?
Thanks - Joel
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