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'[SX] Simple SX48 Question'
2005\11\08@165652 by Tinkern/a

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In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Tinker wrote:

After flipping through the datasheet and a quick forum post search I cant find the answer to this, of course it may be because its an obvious question... The SX48 has 4 sets of VDD/VSS lines, are these there for ease of routing or are they there to distribute the load between different areas of the micro controler? Should they all be connected to VDD/VSS pins?

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2005\11\08@171927 by Peter Van der Zeen/a

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In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Peter Van der Zee wrote:

Hi Chris;
A very good question indeed.

Without being an expert on the subject, my perspective on it is:

I believe the pins are connected together on the die with multple bonding wires, one each per pin. These wires tend to be very light gauge, and hence will have voltage drop on them according to the current flowing in each. So it would behoove one to use the mutiple sets in parallel FOR SUPPLYING THE PROCESSOR ONLY.

Definitely NOT for convenience of routing power/ground to other areas of the board.

Running multiple lines of less power per line also somewhat lowers the emitted EMI because the lines are separated a bit from each other.

Cheers,
Peter (pjv)
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2005\11\08@172241 by Tinkern/a

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In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Tinker wrote:

PJ,
Yes, that was my question exactly. I wouldnt dare to try and pull power from them. Convenience meaning you could supply power from whatever side it happened to be on in a board layout. Just curious if all 4 sets are needed to get full current supply to the processor?

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2005\11\08@213812 by Chris Savagen/a

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In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Chris Savage wrote:

Most people tend to tie them all together under the chip in most designs I have seen.

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2005\11\09@023724 by g_daubachn/a

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In SX Microcontrollers, SX/B Compiler and SX-Key Tool, g_daubach wrote:

I highly recommend to connect all SX48 supply pins to Vdd or Vss ecpecially in order to reduce EMI. If you have a look at the SX48 Develpoment Board, you will notice that each Vdd pin has its own filter cap to ground attached. This further helps reducing EMI.

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2005\11\09@081158 by Coriolisn/a

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In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Coriolis wrote:

Most devices which have multiple Vdd/Vss do so to reduce ground bounce. If only one were present, areas of the chip furthest way from the lines could experience current starvation at higher frequencies becuase they are the last in line, much like if you were at a potluck dinner with an entire football team in line in front of you, there may be no food left when it's your turn. This is an oversimplification of the situation, but it illustrates the point that each supply line should be connected to its own (but connected) path to the supply, and they should not be used as power routing, returning to the analogy this is equivalent to adding another football team after you without adding more food, needless to say they would be quite angry that nothing is left for them.

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2005\11\09@220742 by Tinkern/a

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In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Tinker wrote:

Drilled holes and tied all the VSS and VDD lines to their proper locations, thanks everyone for the comments I just wasnt sure of the reasoning behind it and had never actually had a protoboard in my hands to see how they were connected. Fishing my way through here and there at least one of the projects will go up this weekend and then its on to the next one.

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