Why so many Anode pins on the LM431?

Discussion in 'General Electronics Chat' started by spinnaker, Mar 16, 2010.

  1. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
    I am looking at the datasheet for an LM431. The DIP 8 package has 4 anodes.

    What is the purpose of all of these anodes? Is it just convenience of wiring?

    What should I do with the ones I do not use?
    Last edited: Mar 16, 2010
  2. Bychon


    Mar 12, 2010
    The data sheet I am looking at (Fairchild) shows pin 6 (and no others) as the anode of a DIP 8 package. The SOP 8 package has 2,3,6, and 7 connected to the anode. You should ask the manufacturer if you really want to know why they connected a lot of pins to the anode, otherwise it's a matter of reading their minds, and I'm very bad at that.

    Since all the anode pins are connected to the same place internally, you can do anything except connect them to different places externally. Wire them all together, leave 3 of them not connected, or any combination of the above. My preference is to tie them all together on the circuit board because that gives the chip a tiny bit more area to get rid of heat.
  3. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
    Ooops yes you are right it is the sop 8.
  4. SgtWookie


    Jul 17, 2007
    It was likely the most effective way to deal with heat dissipation issues. That's a clue to make those traces nice and wide, to wick the heat away from the package.
  5. Darren Holdstock

    Active Member

    Feb 10, 2009
    I'd agree with the heat dissipation explanation. Sometimes pins are duplicated to increase current capacity by paralleling the bondwire resistances, or to increase speed by paralleling the bondwire inductances, but of course one would need a minimum of two sets of terminals for this to be effective, which isn't the case with the SO-8 LM431.