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I couldn't find the noise/ripple allowed on power rails of Stratix V Gx in the Data Sheet or any other documentation.
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The Stratix V data sheet has the power supply limits, eg., Vcc = 0.90V +/ 0.03V.
This limit has to be met under dynamic load conditions, i.e., a load step of 10A needs to cause a voltage dip of less than 30mV. The power supply capacitor ESR needs to be low to meet that specification, so the switch-mode power supply ripple current over that same ESR (causing the ripple voltage) is generally significantly smaller, i.e., you don't have to worry about ripple voltage if you have taken care of the transient response requirements.
See this PDF for simulations from LTspice
http://www.ovro.caltech.edu/~dwh/wbsddc/power_supply_design.pdf If you look at the output voltage transient response waveforms, you will see the much smaller output ripple voltage (much smaller compared to the transient dip and peaking).
Cheers,
Dave
