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Topic: Capacitor location (Read 1 time) previous topic - next topic

Hippynerd

I wasnt sure about that, but i had assumed that if sinking, we didnt need the caps, but I wasnt sure.

So are these true statements?

If you are sinking only, then you dont need de-coupling caps.
1 cap will work for many chips, if it is large enough (higher voltage?)
decoupling caps dont have to be soldered directly onto the chips pins i there are large enough traces or wires, and not too far away (an inch?)

Will any type of cap work for decoupling? can I use electrolytic or tantalum? I assume ceramic caps are used because they are inexpensive.

Fungus, FWIW, I generally prefer SMT to THT. I dont have much trouble with either, but smt is faster, easier, and often ends up looking nicer.

fungus


I wasnt sure about that, but i had assumed that if sinking, we didnt need the caps, but I wasnt sure.

So are these true statements?

If you are sinking only, then you dont need de-coupling caps.


You might. When the chip is sinking current they can stop the chip's serial-to-parallel-conversion logic from freaking out if the voltage droops.

Real engineers keep telling me I can never have too much decoupling.


Will any type of cap work for decoupling? can I use electrolytic or tantalum? I assume ceramic caps are used because they are inexpensive.


No. Ceramic are used because they have a faster response time than either of those.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

MarkT


Are you using those chips as current sources or current sinks? If they're sinks you don't need so much decoupling.



No, same currents are changing and inducing EMFs everywhere.  You might want to place the decoupling
capacitor in a different place (close to the ground pin on the chip), and the presence of a ground plane
but no supply plane will affect the symmetry of the situation, but Maxwells equations still apply!
[ I won't respond to messages, use the forum please ]

Grumpy_Mike

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So are these true statements?
If you are sinking only, then you dont need de-coupling caps.

No total rubbish.

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1 cap will work for many chips, if it is large enough (higher voltage?)

No. The voltage rating has nothing to do with it. Large meaning more uF then also no.

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decoupling caps dont have to be soldered directly onto the chips pins i there are large enough traces or wires, and not too far away (an inch?)

It depends on how effective you want them to work. The further they are away from the chip the less good they do, due to the inductance in the lead and the track.

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Real engineers keep telling me I can never have too much decoupling.

You can never have too much decoupling.

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