harpoon
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It is not easy to spec the ripple and what effect it has on the MPU.
It depends on what the MPU is doing internally and how the MPU uses those supplies.
Here is a stab at answering the question :- a) If the MPU is in charge of some really tough PHY (e.g. USB2, PCIe, etc ...), then it is crucial to provide as clean a supply as possible, else eye diagram degradation creeps in ... (though this may not apply to the 3.3V pins)
b) To get an idea of what is tolerable, look at the power management circuit reference of the MPU and check what the ripple spec of the regulator powering the MPU is. Generally 0.5%-1% maybe ?
c) If the MPU has internal regulators (e.g. takes the 3.3V-5V input and drops it down to 1.2V internally), then there will be some spec/info regarding what the internal regulator can tolerate.
d) In your example of 3.3-5V input, wouldn't there be a decoupling cap on that pin ? This decoupling cap will smooth out your sawtooth and provide a semi-stable supply to the MPU.
hope this helps ...
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