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TMUX4827: S1A/S2A Path not working

Oliver McConnell
Prodigy 80 points
Part Number: TMUX4827

We are having a problem with a new part, TMUX4827. The failure mode I am seeing is that when SEL is set to 0, I don’t see our signal pass through the device on S1A to D1. If I set SEL to 1 I can see the other signal come through on S1B to D1. The S1A signal is an RS-232 signal and the signal on S1B is LVCMOS level. The part seems to claim it can support RS-232 levels so I’m not sure why this would be a problem. I can’t probe at pin A1 of the device since it is a BGA, but I can probe the net and see a signal toggling at the pin A1 net, but nothing coming out of pin B1. Do you have any idea what would cause S1A to fail, but S1B to succeed?

Also, how do you determine the orientation of the part? It seems to have a mirror like finish with no clear indicators of any kind on the top that I can see.

  • 0
    TI__Mastermind 18135 points

    Hello Oliver,

    Can you please share a schematic of your system and the scope shots you are getting?

    This will help a lot in resolving your issue.

    Thanks,

    Nir 

  • 0 in reply to Nir Gilgur
    Prodigy 80 points

    S1A to D1

    S1B to D1

  • 0 in reply to Oliver McConnell
    Prodigy 80 points

    I have also tried injecting a square wave with my signal generator into D1 and measuring at S1A. I see the signal begin to be distorted like this once I reach 4Vpp so it seems to me like the part can't actually support the beyond the rails inputs that it claims.

  • 0 in reply to Oliver McConnell
    TI__Mastermind 18135 points

    Hello Oliver,

    I tried to replicate your setup as close as I could. The only difference is that I am sending a square wave to the S1A pin of -5V to 10V instead of -5V to 12V like in your setup.

    As you can see below, in pink is the signal on the S1A pin and in blue is the signal on the D1 pin.

    This is the response at 40kHz. The signal is not perfect, but it is a bit better than what you were getting in your system.

    After decreasing the frequency to 10kHz the signal looks much better. 

    These two responses closely correlate to what shown in the datasheet: 

    According the datasheet spec, the signal will remain stable under 50kHz depending on the voltage signal swing.

    There seems to be an issue with the device behaving unexpectedly with square waves. When we changed it to sine waves it worked fine, it was behaving according to the datasheet spec. 

    Regarding the orientation, the finish is glossy but there is an indicator on the top left of the device. 

    Thanks,

    Nir 

  • 0 in reply to Nir Gilgur
    Prodigy 80 points

    Ok, this makes sense given the frequency limitations. Our RS-232 and UART implementation defaults to baud rates of 115200 which is clearly far beyond the capability of this part. We had to slow things down to a much slower rate to get this part working. The datasheet claim of supporting RS-232 is not a reasonable claim considering RS-232 standard rates go all the way up to almost 1MHz.

  • 0 in reply to Oliver McConnell
    TI__Mastermind 18135 points

    Hello Oliver,

    I appreciate the feedback. I will talk with the team here regarding the datasheet claim.

    Thanks,

    Nir