Placing a caps as close as possible to a chip - Electronic Circuits Projects Diagrams Free

Screech · 13th October 2005, 08:07 AM

So, I ve been advised to place caps as close as possible to Ic's.
These are 100nf caps, for decoupling, I guess.

How do I do it?

A Place the cap as close as possible to the positive pin.
B Place the cap as close as possible to the negative pin.
C Place the cap half way between the positive and negative pins.

aibelectronics · 13th October 2005, 08:42 AM

what matters i think is not how close it is to the +ve or -ve pins put the absolute length of the capacitor leads. the aim is just to reduce the inductive effect of long leads.

Oznog · 13th October 2005, 09:57 AM

As a general "style" recommendation, I'd put that cap right on the end of the top of the chip, its pins would be closest to 1 and 14 of the IC. Just seems more natural and easy to recognize when placing. If you do it consistently then it's an obvious cue to which direction to orient the IC.

Screech · 13th October 2005, 10:20 AM

I could have drawn many combination but, I'm just trying to find out what works best, electronicly, if i had to pick 1 of the 3 pictured.

**Nigel Goodwin** · 13th October 2005, 11:37 AM

Quote:

Originally Posted by Screech

I could have drawn many combination but, I'm just trying to find out what works best, electronicly, if i had to pick 1 of the 3 pictured.

All the same really, don't get obsessed about petty details :lol:

bryan1 · 13th October 2005, 11:51 AM

Hiya Screech,
I agree with Nigel on this, but when I use any dip component I always use a socket for the chip and I usually put a decoupling cap inside the socket and solder the cap to the socket before I solder the socket to the board. I found this tip ages ago on the net and found it to be handy. Off memory you can get sockets with caps already installed.

Cheers Bryan

mstechca · 13th October 2005, 12:27 PM

For generic purposes, any of the 3 schematics can be used. However, if capacitance is such an important issue (like if you were doing an RF circuit), and you wanted the lowest capacitance and inductance, you want to create the shortest path. The easiest way for the shortest path is to connect one pin of the capacitor to the VCC pin of the IC, and the other pin to GND pin of the IC. you can make tracks go under the IC as well.

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13th October 2005, 08:42 AM	(permalink)
aibelectronics	reply what matters i think is not how close it is to the +ve or -ve pins put the absolute length of the capacitor leads. the aim is just to reduce the inductive effect of long leads. __________________ Everybody can but not everybody will.

13th October 2005, 09:57 AM	(permalink)
Oznog	As a general "style" recommendation, I'd put that cap right on the end of the top of the chip, its pins would be closest to 1 and 14 of the IC. Just seems more natural and easy to recognize when placing. If you do it consistently then it's an obvious cue to which direction to orient the IC. __________________ I thought what I'd do was I'd pretend I was one of those deaf-mutes.

13th October 2005, 10:20 AM	(permalink)
Screech	I could have drawn many combination but, I'm just trying to find out what works best, electronicly, if i had to pick 1 of the 3 pictured.

13th October 2005, 11:51 AM	(permalink)
bryan1	Hiya Screech, I agree with Nigel on this, but when I use any dip component I always use a socket for the chip and I usually put a decoupling cap inside the socket and solder the cap to the socket before I solder the socket to the board. I found this tip ages ago on the net and found it to be handy. Off memory you can get sockets with caps already installed. Cheers Bryan __________________ " The only way to avoid human error is to avoid the use of humans"

13th October 2005, 12:27 PM	(permalink)
mstechca	For generic purposes, any of the 3 schematics can be used. However, if capacitance is such an important issue (like if you were doing an RF circuit), and you wanted the lowest capacitance and inductance, you want to create the shortest path. The easiest way for the shortest path is to connect one pin of the capacitor to the VCC pin of the IC, and the other pin to GND pin of the IC. you can make tracks go under the IC as well. __________________ -=: The best low-priced components to troubleshoot with are the speaker and the LED :=-