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SN74LXC2T45: Incorrect Voltage Level

Talal Khalil
Prodigy 115 points
Part Number: SN74LXC2T45

I am using the SN74LXC2T45QDCURQ1 IC with the following connections:

  • VCCA connected to +3.3V
  • VCCB connected to +1.8V
  • DIR connected to GND (B to A)

Initial testing show correct translation. However, after further testing, A1/A2 don't reach +3.3V (measured either 0V or +2.5V - which are both incorrect).

What would cause this behavior? 

Thanks.

  • 0
    Guru 257450 points

    Is there a load? What is the signal frequency? Did you measure with an oscilloscope or a multimeter?

  • 0 in reply to Clemens Ladisch
    Prodigy 115 points

    Yes, there is a load. This shifter is used for reset signals. I measured the level of A1/A2 via a multimeter and that's where I saw 0V the first time and +2.5V the second time. I suspect the IC is getting damaged somehow but I want to understand the root cause. 

  • 0 in reply to Talal Khalil
    TI__Mastermind 25090 points

    Hi Talal,

    If i understand correctly, B to A translation previously worked with both outputs for 3.3 V.

    However after a few tests, the outputs measured 0 V sometimes and 2.5 V other times i.e. with load and setup unchanged.

    I suspect a short (from going above the datasheets abs max rating) and would confirm if replacing the unit solves the issue. If not, help confirm if VCCA is in fact measuring 3.3 V when incorrect voltages are measured, thanks.

    Best Regards,

    Michael.