Discussion point: Question 2 (Bypass Capacitors)

How to choose or calculate bypass capacitors values in schematics?

Response:

Bypass Capacitor value depends on AC ripple and noise frequency on the PCB. Generally bypass capacitors will be used at mid to high frequency ranges mid ranges 0.1uF , using capacitance of 0.01uF which helps to filter higher frequencies than with 0.1uF is also preferred. If a designer wants to use more effective bypassing for wider noise bandwidth signals use array of bypass capacitors. Bypass capacitors provide a very low impedance path for noise and helps to sustain current surges. The major point designer has to remember is that various boards have different noise levels and the usage of Bypass capacitors differ. One of the most common application of bypass capacitor is using them close to the micro controller pins or any other part of the circuit where local noise need to be filtered. One way to select a frequency to bypass maximum frequency of operation of micro controller and it's higher order harmonics (for example till 5th harmonic). The same bypass capacitor used at the output of the power supply helps to reduce the AC component. The important consideration for this bypass capacitor is that it should be placed as close as possible to the power pin such that inductance can be reduced. A ceramic capacitor is the most preferred capacitor for Bypass capacitors as they have the lowest ESR while electrolytic capacitors can also be used

After deciding on the highest frequency to filter, use the generic formula C= 1/2*pi*f*Xc