Decoupling capacitor

 ðŸ‘‰What is decoupling capacitor ?


In electronics we use some circuits which are highly sensitive to current and voltage spikes, voltage fluctuations and electrical noise we need to protect these devices. And capacitors are used to filter voltage and also they protect microchips from electrical noise. So, these capacitors which are used to protect circuit from external noise and voltage spikes and fluctuations are called as decoupling capacitor. They separate device from other circuit to which they are connected. 


👉Where to place decoupling capacitors on PCB ?

These circuits are placed as close as possible to microchip. They also provide extra energy to the IC's and remove disturbances to the logic signal. 

What type of capacitors we should use for decoupling ?

1. Ceramic COG : small, low loss

2. Ceramic X7R : small, low loss and higher values than COG

Above types of capacitor's are mostly preferred in RF decoupling applications.

3. Electrolytic capacitor from 0.1uf to 10 uf

Note : Mostly preferred decoupling capacitors are X7R ceramic capacitor as they show less change in capacitance

👉How to calculate value of decoupling capacitor ?

Capacitor filter voltage but in selecting and calculating by pass capacitor important parameter is its supplied current.

As  C = I ( dt / dv )

Where, I is current needed to switch from low to high by pin mentioned in datasheet of microchip, dt is time required by capacitor to charge in line i.e. risetime and dv is maximum ripple voltage 

when we need to switch in multiple levels then N is also added which is directly proportional to capacitance

C = (I*N*dt )/dv

👉Why 0.1uf is mostly preferred decoupling capacitor and is it okay to use 0.1uf in all circuits ?

0.1uf capacitor is not always answer but most of the parameters of microchips are universally defined and 0.1uf is answer to that. There is also one major reason of using 0.1uf as a decoupling capacitor is it's graph of vcc line disturbance to frequency which is constant for 5 VDC and most of microchips work on 5VDC.

Selecting a proper decoupling capacitor is important for any PCB design and if selection or calculation of this capacitor get wrong then it may ruin your design.


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