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Question on grounding capacitor

Anonymous
Anonymous

Other Parts Discussed in Thread: TVP5146

Hi All,

 

I would like to ask a question on grounding capacitor.

 

 

 

 

I have noticed that in sheet 28 – TVP5146 page of EVM6437 schematics, there seems to be a regularity that:

1.    Analog ground has more parallel capacitors connected than digital ground.

2.    The smaller voltage it is, the larger number of capacitors it requires.

 

Ground

Analog

Digital

3V3

0.1uf x 4

0.1uf x 3

1V8

0.1uf x 6

0.1uf x 4

 

So is this a rule? What is the reason behind this?

 

N parallel capacitors have an effective capacitance equal 1/N of one’s. So in the case of 0.1uf x 4 → 0.025uf, is the choice of such four parallel capacitors, rather than one 0.025uf capacitor, dictated by the market availability/popularity of capacitor type rather than the pure calculation?

 

 

 

Thanks,

Zheng

  • 0
    Genius 3575 points

    0.1 uF caps are typically used as "bypass" capacitors to decouple local current spikes from a distance source.  Notice how there is one capacitor for each pin that takes the corresponding voltage source... it is common practice to show these caps together on a schematic for neatness sake.  If you examine the layout, you will probably find these caps close to the input pins.  Again, it's a fairly common practice to have one bypass capacitor per power pin on a part.

  • Anonymous
    0 Anonymous in reply to MattLipsey

    Dear Matt,

    This is indeed a wonderful answer. I checked power pins of TVP5146 one by one and found this is exactly the case.

    Thanks very much.

    Zheng