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SN74HC540: No function with latest date codes.

Bob Housh
Prodigy 10 points
Part Number: SN74HC540

Tool/software:

We have used the TI: SN74HC540DWR for a while and are now having issues with the operation of the part.

The parts were x-rayed and it appears that there has been a die shrink.

Can you verify and provide any changes in function?

With new parts (date code (37CFEFK) the IC appears to load down the 5V Line.

When we replace the part with older parts (date code 14AHGJK) units function correctly.

  • 0
    Guru 268180 points

    The new die has a smaller typical propagation delay (similar to that of the SN74HCS540) and a little bit of hysteresis at the inputs. The guaranteed datasheet limits are  the same.

    What exactly do you mean with "load down the 5V Line"? How much current?

    Do all inputs have a valid logic voltage? Do the edges conform to the Δt/Δv limit?