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SN74AHCT1G04: Failure Mode

Brian Wang0928
Genius 11610 points
Part Number: SN74AHCT1G04
Other Parts Discussed in Thread: STRIKE

My customer found a logic problem(SN74AHCT1G04DBVR) on existing products of motor driver.

Application: servo Motor

Sub-System: Inverter Logic for IGBT Braking application.

Problem: When inverter logic is fail, the IGBT will be always turn-on and braking resistor is continuously having power dissipation and heating. As a result, it could cause something damage on the power board.

After inverter logic was damaged, either VCC is shorted to OUTPUT or GND is shorted to OUTPUT

 

Failure rate: TBD, it’s low now.  

Question: Besides the either VCC or GND is shorted to OUTPUT pin with existing defective devices, what else? Is it possilbe that the device is in high impedance or OPEN status after device is damaged? Please advice. thanks.

  • 0
    TI__Genius 16725 points
    Hi Brian,

    So we can't guarantee how a part will fail if something happens. There are lots of factors that can cause it to fail in different ways. Besides Vcc or GND being shorted to the output, it is possible that the device becomes open or shorted.

    Thanks!
    - Karan
  • 0 in reply to Karan Kotadia
    TI__Genius 11610 points

    Hello Karan,

    Thanks. Regarding to this failure issue, The failure mode of the OUTPUT shorted to GND is NOT allowed since it could cause something device damaged.

    Here are the following actions. please advice if any.

    1. To look for if any TI logic device which is p2p compatible and can support the "OPEN status/High Impedance" once device is damaged with unexpected behavior and failure cases. Please advice.

    2. What's the workaround solution to avoide the device's OUTPUT pin is shorted to GND pin after inverter logic is damaged. Please advice.

    3. We'll send the defective samples to CHINA CQE for F.A.

    Pls find the application circuit here.

    When the OUTPUT of the inverting logic is shorted to GND during failure, the IGBT is at "ON status" for a long time and the braking resistor has unexpected power dissipation. It could cause other problems with heating on the board.     

  • 0 in reply to Brian Wang0928
    TI__Guru* 96591 points

    Hi Brian,

    As Karan said, we do not guarantee failure modes of our devices.

    We can only guarantee operation of our device within datasheet standards. That is only for normal operation, and definitely not after a catastrophic failure.

    It is the responsibility of the customer to design their system such that a failure of a single device does not result in a catastrophic failure of their entire system.

    I would recommend finding the _cause_ of the failure  What are they doing to our device to make it fail?  Is it an ESD strike?  Is Vcc/GND being reversed?  Is the temperature too high?  The root cause must be found and addressed to _prevent_ the failure.

  • 0 in reply to Emrys Maier
    TI__Genius 11610 points

    Thanks. The defetive sample is found in the field and end-customer site and my customer where they haven't duplicated the problem yet. however, it will be sent to TI for FA. Before that customer'd like to know the how's the internal circuit related to the shorting loop of defetive part. Is the ESD diode damaged or something parts?

    Could you share it to us for customer inquiry?

    Regards,

    Brian

  • 0 in reply to Brian Wang0928
    TI__Guru* 96591 points
    Hi Brian,
    Once the FA is complete, we will provide a detailed report.