I'm not sure if this is a stupid question, but I'd still prefer to ask than regret it later. I'm designing a PCB with the CJ7805 which, like the LM7805, can supply a steady 5 volts. In this case, it's to power a Teensy 3.6. There's a recommendation to place a 100nF capacitor between the Vin pin of the Teensy and ground. I already have capacitors (100nF and 330nF) situated around the CJ7805 as specified by the datasheet. I was thinking of placing a capacitor for the Teensy, but I was wondering if that would affect the overall performance of the CJ7805 since it would change the net capacitance? Or maybe capacitors work differently when placed far apart on a PCB? Would I even need to place additional capacitors on the PCB when it's already being monitored by one capacitor? I've seen boards use soo many capacitors before, and I'm getting a little confused. I'm new to PCB design so I'm still trying to find and understand the proper ways of keeping noise to a minimum. Any help would be appreciated. Thank you!
Best Answer
The regulator needs a bypass capacitor to be stable. The Teensy needs one too. The farther a capacitor is, the less effective it is. If there is 1cm between regulator and Teensy, you may only need one. If they are 1 meter apart, you definitely need two. Since they are on same PCB just draw both and you can choose later to leave one out.