• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 20 subscribers
  • Views 1540 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

SN74LVC2G14: Schmitt trigger failure - fault finding assistance

Robert Gilmore
Prodigy 20 points
Part Number: SN74LVC2G14

I have a product in development that uses the SN74LVC2G14 Schmitt trigger to convert the output of an optocoupler to a square that is then transmitted directly to a micro-controller on a separate PCBA via a ribbon cable. See a section of the schematic below.

We have a failure that has occurred in 3 units in the past month. However it has not occurred in the past 2000 units produced. In some cases the Schmitt trigger fails and heats up, in another it did not heat up. In both cases, no output was observed from the Schmitt trigger. Could these be fault devices? 

Could you please offer some advice on fault finding this device? And any advice on our implementation? I appreciate this is very little information to offer recommendations. However, please ask any question required and I will provide further information. 

Other questions:

Should there be resistors on the output of the Schmitt trigger that is connected directly to the micro-controller? 

This product has an ignition spark. How could fluctuation in GND affect the device. 

  • 0
    TI__Genius 16735 points

    Hi Robert,

    What kind of load is the LVC device driving? If the output current of the device is greater than recommended conditions, I can see a potential reason for the outputs of the device to get damaged. If the output current is really large, adding a resistor on the output of the device will help.

    There are many ways in which GND fluctuation will impact the device. How much GND fluctuation do you expect? There are diodes from GND to the input and the output. So if GND voltage fluctuated to above the input or output voltage, then current will flow from GND to the input or output. If this current is greater than the amount giving in the ABS Max table of the datasheet then this is also a cause for concern.

    Thanks!

    -Karan