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TS3A24159: UART Switch Issue

Dan Hughes
Prodigy 20 points
Part Number: TS3A24159

Dear expert,

I'm using the TS3A24159 as a switch between 2 Uart devices.  I'm seeing about a 2% failure with these devices in production and cannot seem to pinpoint the problem.  When both devices are connected (via external cable), only the NO device communicates with the host processor.  If I only connect the NC device, it works fine and same if both or only the NO device is connected.  Please see schematic below and let me know if you see anything I can check that could potentially cause this problem.

When verifying the signals with an oscilloscope, the device that is not working never sees the TX from the host indicating that the switch isn't closed or somehow between states.

Operating parameters:

9600 BAUD

1mS delay between communications and switching

End devices are 2 of the same microcontrollers.

Regards, 
Dan Hughes

  • 0
    TI__Mastermind 45350 points
    Dan,

    Let me see if I understand the problem you are seeing.

    Case 1 - Fail
    Connect two devices to both J1 and J2
    Communicate to device on J1 = failure
    Communicate to device on J2 = no issue

    Case 2 - Fail
    Connect one device to J1
    J2 is not connected
    Communicate to device on J1 = fail

    Case 3 - Pass
    Connect one device to J2
    J1 is not connected
    Communicate to J2 = no issue

    1) You mention the failing path does not see TX signal but does it see RX? It might help if we can see the IN, COM, NO and NC, on one screen when you are communicating and then switching when you are not communicating.

    2) What is the voltage on the IN1/2 control pins? Is it possible that the 47k pull down resistor isn't strong enough to pull down the device controlling the UART_CTL node? What is driving the control signal?

    3) Does removing the IC and replacing it with a new one solve the issue?

    4) Does removing the IC and shorting the connection to the path that is not working solve the issue?

    5) If you take the switch IC off the failing board and replace it on a failing board does it cause the board to fail in the same manor?

    Thank you,
    Adam
  • 0 in reply to Adam Torma
    TI__Mastermind 45350 points
    Dan,

    Have you made any progress on the debug?

    Thank you,
    Adam
  • 0 in reply to Adam Torma
    Prodigy 20 points

    Hi Adam,

    Sorry for the delay in getting back with you.  I'm in the middle of moving offices.

    The unit I had with these symptoms ended up having the 5v and 3.3v lines crossed in the cabling between the 2 PCBs.  It's interesting that the boards react this way but to no fault of the TI TS3A24159 part.  I have others that are also having these same symptoms so once I get resettled and unpacked, I'll get those back out to continue the investigation. 

    Thanks for your patience.

    Dan Hughes