FreeLists / si-list / [SI-LIST] Re: decoupling

[Ray Anderson <Raymond.Anderson@xxxxxxx>]

>>
>>         The maximum dynamic current swing is from 15 to 20 amps
>
>Ray,  how do you obtain the 15 to 20 amps number, I am a little confused
>on how to go about obtain the transient current value.
>

The transient current value is circuit dependent. In a typical
microprocessor the core power requirement might be say 30 amps DC,
however the transient current might only be 5 amps when the core
current consumption goes from 25 amps at idle to 30 amps when the processor
is doing something that requires a lot of current.

There are some processors that consume huge quantities of DC current,
but whose transient requirements are rather modest just as there some
processors who have modest DC requirements but have large dynamic
swings.


The dynamic current is a function of both the actual circuit/logic
implementation as well as the application code that is executing.
Some code is rather benign and doesn't cause huge current transients
while some applications can be quite brutal as far as causing transient
current changes.

The dynamic current can be determined either by measuring the current
transients (an inductively coupled current probe and an o'scope are
good for this), or alternatively if one is clever enough and has the
proper spice models you can determine the delta I from simulation.
As a practical matter, measurement is usually the only viable method
in most cases.

-Ray 

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