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LM317: On the LM317 in the KTT package (TO-263) is pin 2 connected to thermal tab internally?

Mark Sauerwald
Prodigy 80 points
Part Number: LM317

I use the LM317 in several designs, and always tie the thermal pad to Pin 2 on my PCB layout.   I am working on a design which will be fabricated on an aluminum board, so I only have a single layer to route my circuit.   In this design, it would be very useful to not connect the thermal pad to pin 2, allowing me to run a trace between the two.   Is this OK? - Does it make a difference where I draw the bulk of my current from - Pin 2 or the Thermal Pad?

Thanks

  • 0
    TI__Guru 55940 points
    Hi Mark,

    The Thermal Pad and Pin 2 are electrically connected in the KTT package. As such your layout should be okay if you are running a trace between the two. It does not make a big difference which you draw the bulk of your current from; however, since the main heatsink for this device is the metal connected to the output from a thermal perspective it would still be good to connect as much metal as your application allows to the Thermal Pad.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Prodigy 80 points

    Thanks Ryan!

    Since I am on an Aluminum board, which will be mounted directly to the bottom of a large aluminum case, I think that I should be OK thermally with the main heat path being straight down. 

    Mark