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TMUX7462F: Voltage on floating Source and Drain Pins

David Bill
Prodigy 30 points

Part Number: TMUX7462F

Hello,

I use the TMUX7462F for protecting my measurement electronics from above 4V and used the following setup for testing:

When VFP is left floating, D1 can be measured with GND potential. However, if I now connect 3.3 V to VFP for setting the overvoltage level, there are 110 mV at D1. Further, at the floating pins S3, D3 and S4, D4 I measured 160mV after applying voltage to VFP.

Can you please comment whether this is expected behaviour of the TMUX7462F? Is there some chip-internal circuitry, that leads to a feedthrough from VFP to the source/drain pins?

Thanks four your support.

Best regards,

David

  • 0
    TI__Genius 10552 points

    Hi David,

    In the first case where you measure 110 mV is S1 floating? This issue may be tied to the fact that I/O's are left floating when measuring at the drain. If that's the case, then I'd recommend grounding unused I/O's. 

    Thanks!

    Alex

  • 0 in reply to Alex Vish
    Prodigy 30 points

    Hey Alex,

    thanks for your response!


    Sorry, my sketch in the initial post above was not correct, I updated the draft!
    I have 105 kOhm connected from S1 to GND and 5 kOhm from S2 to GND. Further, also the DR pin and the FF pull-up are connected to the VFP signal.

    After applying 3.3V at VFP, the 110 mV can be measured at S1 and D1, whereas the floating Sx/Dx pins are at 160 mV.

  • 0 in reply to David Bill
    TI__Genius 10552 points

    Hi David,

    Thanks for the additional info! This is definitely unexpected behavior. May I ask you to please provide waveforms of the S1 to D1 path? As well as confirming voltage levels for Vfp?

    Thanks!

    Alex

  • 0 in reply to Alex Vish
    Prodigy 30 points

    Hi Alex,

    here are the waveforms:


    1) S1 with Vdd = 12 V, VFP = not connected

    2) D1 with Vdd = 12 V, VFP = not connected

    3) S1 with Vdd = 12 V, VFP = 3.3 V

    4) D1 with Vdd = 12 V, VFP = 3.3 V

    5) VFP after connecting 3.3V source

    Regards,

    David

  • 0 in reply to David Bill
    TI__Mastermind 35648 points

    Hey David, 

    I noticed some oscillation on the inputs here. Are you toggling anything while doing this test? The device doesn't have an internal oscillator so It's not clear where these oscillations are coming from. 
     
    I believe Alex mentioned this above, but did you try grounding all the floating I/O's and check the results? I wonder if you're picking up some noise and it's coupling onto your inputs. 

    Thanks,
    Rami