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Willie Chan

Prevent Your Next High-Flying Product Launch From Being Grounded

Willie Chan
Willie Chan
Willie Chan
5/24/2013 4:23:10 PM
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Blogger
Re: Rise times in GHz region
@eafpres: Thanks for the comment. In the scenario I describe, I focus on the intermediate power bus where voltage spikes in the several or tens of volts are caused by other abrupt loads such as solenoids, motors, fans, hot plugged daughter cards or on the upstream side a brownout from the utility or switching from one power supply to another i.e. auxiliary power or battery power to main power.

While there could be some noise coupling of high frequency components from high speed data lines, their energy is relatively low such that they would easily be absorbed by the bypass capacitance at the output of the DC/DC regulator. Moreover, good PCB layout practice would dictate a short trace length between the output of the DC/DC regulator and the digital processor to minimize any energy coupling into the power rail. I hope I answered your question.










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WKetel
WKetel
5/23/2013 6:57:22 PM
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Artist
Those nasty little incoming power disturbances
I suppose that the constantly dropping supply voltages do make greater demands on the secondary regulators from those intermediate power busses. And for all of those systems designed with minimum total cost as the primary design objective, as well as the secondary target, I have no sympathy at all. A bit of filtering at the input to the regulator will not only slow many of those spikes down to a much more manageable speed, and much lower amplitude, the same filter will prevent noise from the switching regulator from traveling upstream and causing problems elsewhere. Just because the internal regulator does not need to meet the same requirements as the AC line input regulator module does not mean that designing unfiltered junk should be the rule.

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eafpres1
eafpres1
5/16/2013 11:36:37 AM
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Blogger
Rise times in GHz region
Hi Willie--interesting post and situation created by the evolution of voltage standards within industries.

Question for you: Over on The Connecting Edge (sister site) there has been a 2-part tutorial on signal spectra basics.  You can find Part 2 here:

Basics of Signal Spectra, Part 2.

The point has been made clearly that for digital pulses, there are high frequency components of significant magnitude.

Just doing a back of the envelope calculation, is there a potential that in an RF system the 500 nS protection time might be insufficient?  I have to admit I don't really know what to expect in terms of voltage transients you are referring to.

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