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TRS3237E: About failure mode when destruction due to overvoltage occurs on RS-232C bus

Part Number: TRS3237E

Hi all,

There are two questions about the failure mode when a breakdown due to overvoltage of DC 26.4 V exceeding the maximum absolute rating occurs on the RS-232C bus of TRS3237E.

1. What about the situation of destruction occurred about the driver and receiver of  RS - 232C bus ?
    short to VCC or GND, or open state, etc.?

2. When breakdown occurs, is there a possibility that excessive voltage or current will flow in PINs on the TTL side?
 Is there a possibility that the device connected to the TTL side is destroyed depending on the failure situation?

Regards,
Toshi
 

  • Hi Thoshi,

    thanks for reaching out. I guess you are referring to the V_O Output Voltage range of the Driver and Receiver. Do I understand this correctly?

    Kind regards

    Dierk

  • Dierk-san,
    thanks for your response.

    It is assumed that the terminal of RS-232c BUS is shorted to the + 26.4 V dc power supply.
    Since it is a voltage exceeding the absolute maximum rating of the driver and receiver of TRS3237, the possibility of a breakdown is predicted, and I wanted to know what kind of phenomenon it would happen when a breakdown occurred.

    Best regards,
    Toshi
  • Hi Toshi,

    thank you for this detailed explanation. This is a very good question since this is affecting directly the internal circuits structure it is not easy to make a statement just by looking up the schematics. Let me do some practical test in our laboratory and I'll come back to you with results this week.

    Thanks for your patience.

    Kind regards

    Dierk 

  • Dierk-san,
    I appreciate your cooperation. .

    We am looking forward to the results.

    Best regards,
    Toshi
  • Hi Toshi,

    As a status update:

    I am waiting at the moment for samples. The package of the devices which where available are not compatible with test equipment I need for this test so I had to order a different package type of the device.

    I'm looking forward to receive the devices beginning of next week and do the test as soon as possible.

    Kind regards
    Dierk
  • Hi Toshi,

    thank you very much for your patience. I have finished the tests and the result is pretty clear. I did a voltage over current plot to visualize the behavior of the RS-232 driver and receiver of the TRS3237E.

    Info:

    Vertical axis the voltage 5 V/Div, horizontal axis the current 5 mA/Div. The plot shows the RIN or DOUT pins behavior. 3 devices has been tested with the same results.

    Result:

    For the receiver RIN: The device was stressed up to 30 V on the BUS and the device is still functional. The linear plot represents internal 5 kOhm input resistor.

    For the driver DOUT: The Driver is strongly affected by the voltage applied to the BUS. The differential signals get distorted if a voltage from 9 V up to 17 V applied to the BUS so that no function is possible. But when the voltage gets decreased again the device returns to normal operation without damage.

       

    For voltages in the range of 17 V to 20 V a breakthrough happens and the DOUT pin gets shorted to ground. Once this occurs the device is broken and no operation is possible the Vcc pin will draw current until the device gets destroyed.

    I hope this is helping you out, let me know if you need anything else!

    Kind regards

    Dierk

  • Hi Dierk-san,

    Thank you so much for the test results. This is very helpful to understand the behavior of IC when overvoltage is applied.

    Would you please give me the answer for the second question as below?

    2. When breakdown occurs, is there a possibility that excessive voltage or current will flow in PINs on the TTL side?
     Is there a possibility that the device connected to the TTL side is destroyed depending on the failure situation?

    Thanks and regards,
    Toshi
  • Hi Toshi,

    I revisited my bench and did further tests. In order to prove if there is any danger for the logic side (TTL) I applied 30 VDC to one of the DOUT and RIN pins and measured if any of the DIN or ROUT pins (logic side) show any abnormality. All the other supplies where removed from the TRS3237E to see if the RS-232 BUS is somehow shorted to one of these pins.

    The result is I could not see any voltage between the logic pins and the RS-232 BUS pins. As far as I can tell from these results I can not see a possibility that devices connected to the logic side get destroyed.

    Kind regards 

    Dierk