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CD74HC4538: IC geting short VCC to GND

Narayan P Sangale
Prodigy 110 points
Part Number: CD74HC4538
Other Parts Discussed in Thread: LM2672

Dears,

We are using IC CD74HC4538M, IC SN74HCT125D and IC SN65HVD251D 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 and CD74HC4538M is about 5VDC clean and not exceeding. Also IC SN65HVD251D is operating on 5VDC.

Also inputs connected to IC CD74HC4538M is isolated from external inputs by opto isolators.

 

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.

 

Can you please help us to identify;

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
    Guru 257370 points

    Please show the schematic of the circuit.

    Are there other damaged components? (In the image above, a component at the bottom appears to be discolored.)

    If I had to guess, I'd suggest overvoltage, probably on the power supply. Is the LM2672 still working?

  • 0 in reply to Clemens Ladisch
    Prodigy 110 points

    Dear Clemens,

    Thanks for the reply.

    Sorry, I can not share the schematic due to copyright.

    Yes other damaged components are 74LVX125MTC and MC74HC589AD and two IC of CD74HC4538M.

    And I checked LM2672 circuit and it is working after removal of these damaged IC.

    Each inputs of IC's are having clamping diode, series resistors and inputs are coming from either op amp output or schmitt trigger output.

    And these (Op Amp and schmitt trigger) are ok.

    I also checked LM2672 for input power variation and still it is ok. only difference is that LM2672 output is near about 5.1VDC to 5.2 VDC.

  • 0 in reply to Narayan P Sangale
    TI__Mastermind 43440 points

    Hi Narayan,

    If the device is being operated within specs, there shouldn't be any damage to the device. Over-voltage can cause issues like the one you are seeing, and also having slow transition rates at the inputs can cause damage. I would monitor all the signals being applied to the device being damaged to see if you can find anything that may violate the datasheet specs. It seems like several devices are being damaged so its possible its a system related issue. 

    Another option is to start a FA (failure analysis) by working with a dedicated TI sales support or the distributor.