LC Filter Circuit

Due to changes in the Power Module our 3.3 V and 5 V rails from the Backplane will not be as clean as previously hoped for. The 3.3 V rail is supposed to now have a ripple of ~33 mV and the 5 V a ~50mV ripple. While some of our components like the microcontroller, flash memory, and ethernet IC may be fine with this change, our sensors will be affected by this electrical noise. The solution is to have all components that are sensitive to these ripples have their power run through a LC low pass filter. This low pass filter will be able to stop high frequency AC voltage(voltage ripples) from passing through to the rest of the circuit. Using this filter will result in only lower frequency ripples getting through which to the sensors would be considered negligible. 

An LC Filter is made up of an inductor and a capacitor. The values of the inductance of the inductor and the capacitance of the capacitor can be used to find the cut-off frequency of the filter as well as the characteristic impedance. Equation F = 1 / (2π*√(L*C)) gives the cut-off frequency in Hz. Equation Z = √(L/C) gives the characteristic impedance in Ohms. Or this calculator can do it for you.