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Do I need capacitor in my design? - SparkFun Electronics

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By denisbest
#44065
Hello guys,

I am interfacing accelerometer, and design tips suggest that I put decoupling capacitor of value 0.1 uF between Vcc and Vss. I also have power regulator for accelerometer and Vout from regulator has polar capacitor 1 uF.

Do I still need to decouple power inputs with ceramic 0.1 uF?
By Andrew02E
#44066
You don't need one, but it's a very good idea. A capacitor placed near the accelerometer will help stabilize its supply voltage. Ripples in the supply voltage will most likely be reflected in the outputs of the accelerometer, giving you inaccurate readings.
So basically, decoupling capacitor = more accurate readings, no decoupling capacitor = less accurate readings.
Last edited by Andrew02E on Wed Mar 05, 2008 12:20 pm, edited 2 times in total.
By npk
#44067
The real answer is prototype and test. The easy answer is yes do what the design tips suggest.
By denisbest
#44069
Thank you guys!

My board is pretty crowded, just wanted to see if i can have one component less.

I'll leave the part to make sure I won't have to stick it later on when accelerometer readings are off :D
By rdpzycho
#44110
you may go without the 0.1uf..

0.1uf ceramic can absorb high frequency noise much better than the polar one..putting combinations of capacitors in parallel just makes a more effective filter..
By maokh
#44115
Some people think that a giant capacitor will smooth everything out, but they actually just have a lower frequency response. A smaller value may seem silly at first, but its quite useful for filtering high frequencies.

I at least put a small cap between vcc and gnd of an IC if i can get away with it. They dont really cost anything, and id much rather add a useless component than worry about redesigning a board.

There may be lots of capacitors on a board, but the filter will be more effective being as close as possible to the target component. too long of a trace will just pick up noise again.
By rdpzycho
#44172
agreed...

using a network analyzer, the response of the large electrolytic capacitors are only good at the lower frequnecies while the ceramic small ones can filter the higher frequencies..the combination of the 2 is actually good for all designs..

I would normally place caps all over my board if vcc - gnd traces are already long enough, to somewhat localize the current loop to a certain part..

as a good practice put the caps as near as possible to the IC (not more than an inch) then use traces that would not create a large loop area..the inductance of loops does some things to a capacitor's response..