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  • TI Thinks Resolved

SN74LV4051A: Selector lines latching

Prodigy 40 points

Replies: 4

Views: 73

Part Number: SN74LV4051A

Hello,

We are seeing a failure where the selector lines A, B, and C are latching permanently. We typically cycle through various inputs to monitor voltages across our system. However, we are seeing a number of units exhibiting a behavior where the value is the same across all channels. 

We were able to isolate it to the MUX and not the micro.

We have some additional failed boards on their way back to us to examine, but were hoping you might be able to help us understand what might cause the SN74LV4051ADR MUX to latch?

Thanks!!!

Eric

SN74LV4051ADR
  • Damage is typically caused by exceeding some absolute maximum rating, most probably overvoltage at some I/O pin.

  • Hi Eric,

    Could you share signal levels at the Yx, COM, and A/B/C, and what is the VDD for the SN74LV4051A in the system? As Clemens indicated this behavior usually signals that the part was subjected to conditions beyond maximum operating conditions, but I'd like to see if this could be the problem in this application.

    Best Regards,

    Parker Dodson

  • In reply to Parker Dodson:

    Thank you so much for the quick responses!

    Here's what our setup looks like:

    The A/B/C select lines are driven directly by a microcontroller from 0V to 3.3V.
    The VCC is 3.3V with a 0.1 uF bypass capacitor.
    The COM and all Yx signals are continuous voltages ranging from 0V to 3.3V.

    Thanks,

    Eric

  • In reply to 6336380:

    Hi Eric,

    It looks like it isn't an issue of Abs Max, but just in case, what is the current running through the switch in your application?

    Just so I am crystal clear with the issue; when a select line (A, B, or C) are pulled high by the microcontroller, and then when the microcontroller pulls the gate low the select lines remain high, or am I misinterpreting what is happening? Also this doesn't happen on every board, but it's happened on multiple boards?

    The only thing I can think that is possibly happening is that the select lines don't go low, or don't go low enough to release those select lines causing the issue, but I am not sure because if the micro has already been verified as not the problem, I am unsure why the control inputs latch. 

    If it isn't happening on every board, I'd like to look at some scope shots of the select lines as well as the input/outputs of a verified problem board if possible. Because based on your circuit, everything looks like it should work fine, so if you could provide this data it will help look at a more detailed picture of what is happening.

    Best Regards,

    Parker

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