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 Post subject: duplicate pins on pinout?7
PostPosted: Wed Mar 23, 2005 2:40 am 
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Joined: Wed Jan 05, 2005 11:38 pm
Posts: 305
Location: San Diego, California
There seem to be several pins that require the same connections. For example pin's 12, 24, and 54 should all be connected to VDDCORE. And pins 18, 45, and 58 should all be connected to VDDIO. Why don't they just do it all internal on the chip?

pin 12 VDDCORE / pin 24 VDDCORE / ping 54 VDDCORE

pin 18 VDDIO / pin 45 VDDIO / pin 58 VDDIO

Thanks for any info! :)

-Henk Visser


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 Post subject:
PostPosted: Wed Mar 23, 2005 11:58 am 
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Joined: Tue Feb 24, 2004 6:27 pm
Posts: 161
Hello,

just to keep an equipotentiality power supply level in the die.

Rgds
JP


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 Post subject:
PostPosted: Sun Mar 27, 2005 6:40 pm 
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Joined: Thu Nov 25, 2004 6:37 pm
Posts: 7
Location: NJ, USA
To add a bit more info to JP's answer:

traces on a chip have pretty high resistance and if you have only one supply or ground pin and you run it all around the chip neither the ground nor the supply will be what it should be. Tons of spikes and completely different voltage levels.

In addition the lines have to be made very wide to avoid electro migration which increases the die size (= cost).

Juergen


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 Post subject: thank you
PostPosted: Mon Mar 28, 2005 9:00 pm 
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Joined: Wed Jan 05, 2005 11:38 pm
Posts: 305
Location: San Diego, California
Thanks for the posts gentlemen! Excellent!

-Henk


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 Post subject: decoupling cap
PostPosted: Thu Mar 31, 2005 7:45 pm 
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Joined: Wed Jan 05, 2005 11:38 pm
Posts: 305
Location: San Diego, California
If I have power going to one pin on the processors 1 decoupling cap would be suffiecient. But since I have this same voltage going to muliple pins should I have caps at each pin? Or maybe 1 cap right before the all spit off.

Thanks.

-Henk


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 Post subject:
PostPosted: Thu Mar 31, 2005 10:33 pm 
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Joined: Sun Mar 20, 2005 6:46 pm
Posts: 29
Location: MEXICO
Better to have one decoupling cap per pin !!!!! Take a look at the Evaluation Board schematics

_________________
Aaron


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 Post subject: thanks aaron
PostPosted: Fri Apr 01, 2005 1:48 am 
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Joined: Wed Jan 05, 2005 11:38 pm
Posts: 305
Location: San Diego, California
Aaron,

Looking at the Power Decoupling section in the schematic I was not sure on how to approach this becaue I want each decoupling cap as close to the pins as possoble but they group all the caps together and it was throwing me for a loop! :)

Thank you!


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