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LM2940-N: Change in Junction to Ambient resistance value

balaji yoki
Prodigy 70 points
Part Number: LM2940-N

Hi,

We have used one of your low drop out regulators from National semiconductors in our power supply dc -dc conversion.

Part no : LM2940S-8.0/NOPB

As per the National semiconductors datasheet revision Jan 2007 , junction to ambient resistance is 80 degC/W , but when compared with TI datasheet it is 40.9 degC/W

could you clarify the decrease in  junction to ambient resistance between revision?

Also whether LM2940S-8.0/NOPB is active for future designs?

Regards,

Balaji G K.

  • 0
    TI__Mastermind 22610 points

    " ... clarify the decrease in  junction to ambient resistance between revision?"

    The difference is due to the different test conditions (i.e. PCB) used to determine the RΘja value.

    The old National Semiconductor datasheet does not describe the PCB used to determine the RΘja value for the TO-263 package. National Semi typically used a two-sided PCB, one inch square, as the reference mounting for the TO-263, but there is no way to confirm what was actually used.

    Today the TI datasheet version uses the industry standard PCB defined by JEDEC JESD51 specification.

    There have been no changes to the silicon, or the package, that would affect this thermal resistance rating.

    " ... LM2940S-8.0/NOPB is active for future designs?"

    There is no indication today that LM2940S-8.0/NOPB will not be available in the future.