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LM2677: Not sure what to do with device Thermal Pad

Part Number: LM2677
Other Parts Discussed in Thread: LM337

I am using a LM2677 on a new design and wanted to confirm that the “Thermal Pad” on a TO-263 (7) package should be connected to GND.

 

On any of the simple switchers I have run across so far this is the case and of you go to page 26 of the data sheet it looks like U1 has Pin 4 and the thermal pad both attached to GND. I searched the data sheet for any mention of what to do with the thermal pad (electrically speaking)  and couldn’t find anything. Before I go ahead and order PC boards I just wanted TI’s final word on grounding the thermal pad.

  • Hello David,

    I am not sure If I understood your question correctly, this is a thermally enhanced package provides greater design flexibility and increased thermal efficiency in a standard size device package. The package’s improved performance permits higher clock speeds, more compact systems, and more aggressive design criteria. It is designed to eliminate the use of bulky heat sinks and slugs. Hope this helps!

    Best Regards,

    Ankit Gupta

    Application Engineer

  • On page 26, the datasheet tells you to connect the thermal pad to ground.

    The thermal pad is connected to the substrate, which must be the most negative voltage in the device. This is GND (except for negative regulators like the LM337, or opamps with dual supplies).

    (In general, the pad does not need an electrical connection and could be left floating.)

  • OK - thanks!

    BTW: The datasheet that the TI website links to says "SNVS077J –MAY 2004–REVISED JUNE 2016" and on page 26 only shows a layout example so maybe the text about grounding the tab got deleted by mistake in the last edit? Page 11 does have a note for the VSON package stating that the die attached pad (DAP) must be connected to the PCB ground plane but no mention of the TO_263 package.

  • Hello David,

    Answering your question here. 

    Page 26 only shows a layout example so maybe the text about grounding the tab got deleted by mistake in the last edit? - It might be a possibility. I will bring this in a notice to the owner of this device.  Thanks!

    No mention of the TO_263 package - I agree, but the concept applies same for TO packages as well.

    Hope this helps!

    Best Regards,

    Ankit Gupta

    Application Engineer