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Best practices for schematic pins connected to multiple package pins

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I am new to Cadence SPB/Allegro, so there may be something simple I'm missing.
I am trying to set up some basic library components, such as an LM317 regulator.  The regulator comes in two styles we may use, a TO220 with 4 pins (3 pins and the heatsink), and a D-PAK with 3 pins.  In the TO220 package, pins 2 and 4 (the heatsink) are the same.  I want a schematic symbol with 3 pins connected to both possible footprints.

In Part Developer, I can only connect a schematic pin to multiple footprint pins if I set it as a global pin, but then, as far as I can tell, I can't make it show up in the schematic symbol.  Alternatively, I can create a footprint with the same pin number for pin 2 and the heatsink (maybe?), but then I can't reuse the footprint between components. 

Is there a better solution I'm missing?


Originally posted in cdnusers.org by colincross

  • If I understand what you need, you wish to short pins 2 & 4 on the
    footprint to a single pin on the schematic device.

    Please review the attached document and see if this helps.

    Essentially, you'll be adding a PACK_SHORT property to the symbol.


    Jerry


    Originally posted in cdnusers.org by geraldg
    multipin.doc

  • You may also consider the SourceLink Solution# 1816165


    Jerry


    Originally posted in cdnusers.org by geraldg

  • Posted By geraldg on 3/22/2006 5:27 PM
    You may also consider the SourceLink Solution# 1816165 

    Jerry
    Sorry - Please use this SourceLink direct link for Solution# 1816165

    http://sourcelink.cadence.com/docs/db/kdb/1998/July/1816165.html

    Jerry


    Originally posted in cdnusers.org by geraldg

  • Thanks for the link, it solves half my problem.
    However, the result of following the instructions is to create a symbol that looks like it has only 3 pins, but actually has 4, which can then be associated with a footprint with 4 pins.  The resulting symbol then cannot be used with a 3 terminal footprint.  Is there any way to create a single, 3 pin transistor symbol that could allow either a 3 pin SOT-23 footprint or a 4 pin TO220 footprint to be chosen from a part table file, or do I have to suck it up and make two parts in my library?


    Originally posted in cdnusers.org by colincross

  • Well ... from what you're trying to accomplish, this cannot even be considered
    an asymmetrical part. Since you needed to match either a 3 --or-- 4 pin
    physical package, the cleanest method would be to make 2 different components
    and reference their respective JEDEC_TYPE values for the footprints via the
    PTF files.

    Jerry


    Originally posted in cdnusers.org by geraldg
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