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SN74HCT125: IC geting short VCC to GND

Narayan P Sangale
Prodigy 110 points
Part Number: SN74HCT125

Dears,

We are using IC SN74HCT125D in our designs.

We are facing issue of IC getting short VCC to GND (VCC and GND pins are observed shorted together).

We are observing this problem repeatedly.

VCC and inputs of SN74HCT125D  is about 5VDC clean and not exceeding.

Please note that the we have cable length of about 30 meter long which carries 24VDC and from this 24VDC we have generated 5 VDC using DC to DC converter LM2672M_ADJ.

This power supply is also protected with transorb, ferrite bead in series with output and input and output capacitor filters.

Possible causes of IC damage?

What are the parameters which can damages the IC?

Preventive measure and circuit protection guidelines?

Types of Measurements in filed to find out the root causes?

Design support for robustness improvement to avoid failure?

Please see attachment for the IC damage images

  • 0
    TI__Genius 16725 points

    Hi,

    There is not a list of known possible failures I can give you. So its hard to know list of possible failures. Can I see your schematic? I might be able to see if there is a parameter being crossed. Has this happened on more than one device? There may have been some ESD damage which could have shorted something internally to GND. Could there have been damage to your DC to DC converter? 

    If the device is used outside any of the datasheet specs, it is susceptible to damage.

    If the device was damaged due to ESD failure, you can add external ESD protection. The device only comes with enough ESD protection to protect from damage during manufacturing.

    Thanks!

    -Karan

  • 0 in reply to Karan Kotadia
    Prodigy 10 points

    HI, i want to use the same IC. Does it need external ESD protection in case when circuit will be opened and will be able to touch( and I think it will be touched many times) to human body? 

    And which kind of protection is necessary for this case?

    Thank you! 

  • 0 in reply to Orest Hapaliak
    TI__Genius 16725 points

    Hi,

    That is a complex question to answer. Yes you need to add external ESD protection.

    We have an ESD group at TI who I have added to this post and they can help answer this question.

    Thanks!

    -Karan

  • 0 in reply to Karan Kotadia
    TI__Prodigy 360 points

    Hi Orest,

    I have reviewed the information in this thread and I don't see conclusive evidence that the cause of your issues is a transient overvoltage event like ESD or surge although it is a possibility

    In reviewing your case, it looks like there are a couple of possibilities:

    1. An overstress event on the signal or VCC lines that is similar to a DC event in the >1mS domain in which case you may either need to have a overvoltage protection that limits the voltage on the signal and voltage lines to <7V (abs max of IC) or find a way to debug why this is happening

    2. An overstress event that is a transient in the uS domain that is similar to ESD or Surge event on the signal lines or from the DC to DC. This is where I may be able to help. However for the best solution it would be helpful to know what is happening but without that information here is a possible solution

     >>You could place a surge/esd diode on the VCC line to help clamp the overvoltage to prevent damage to them. The TPD1E10B06 would be a good options for all the lines or you could place a TVS0500 for more protection on the VCC line.

    Thanks!

    Obi Oji

    TI ESD/Surge Protection (ti.com/esd)