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Finding peak current of microprocessor

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eem2am1

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Hello

I do SMPS to supply microprocessor.

It takes 2.6A, but we don't know if their are short periods where it may draw more current than this.

Is there a function on most scopes which would allow us to scope a current sense resistor and "remember" the maximum reading?

..ie leave the scope connected for 24 hours and "catch" any current peaks?
 

You no need to bother about it i think, there may +/- 15 tolerance. We can't expect more tolerance of drawing current of the controller. Better you refer the datasheet of the micro controller you are using. There they specify the absolute maximum current and power ratings. You select the SPMS accordingly. For sefer side, design SMPS having atleast 20% more than rated.
 
Power draw is code-mix dependent. If it draws 2.6A "DC" then
switching peaks are much greater every cycle. Presumably the
abs max, rec max currents are greater than tested actuals and
you could (over)design a supply based on this. You might inquire
of the part vendor and see if they have either better guidance
or perhaps a test code block that is calculated to give a worst
case load step (it is not simply the max DC load that is
interesting; are you able to step over a full scale load dump
and not overshoot the supply voltage so that it pops the
uC, or a sag so much in the opposite case that the thing
flakes out for timing violations).

We got code for an FPGA to do this and the step you can
program in, if you try, is huge.
 
as dick_freebird implied, the concern generally isn't what the peak current draw is, but rather what the maximum load step is. Even if your supply is rated to 2.6A, is the load jumps from 0.1 to 2A in a few uS, then your rail will likely droop momentarily and may cause brownout. So you should do transient load testing with a switched dummy load to verify it.

Many scopes, you can use digital persist, which causes traces to leave a ghost behind them which last forever. So set the scope on auto triggering at a fast sample rate, probe current, turn on infinite persist, then leave it alone. You'll see the persist trace of the highest current peak. You just have to make sure the triggering won't miss any short events.
 
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