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THVD1450: THVD1450 failure issue

Junji Takiguchi
Prodigy 250 points
Part Number: THVD1450

Good day all.

 

At now, we are facing that THVD1450 failure issue.

Our product has RS-485 I/F between product and host PC system.

In production line, failure products shows low RS-485 signal amplitude.

To detect this failure in other process, we added special check process.

At that station, we measure a resistance value between RS-485 terminals and GND.

In this process, failure products were found as low resistance value.

(NG ratio is less than 1%)

 

Detail of failure symptom

　Resistance value between differential signal output pin and GND is very low.

(about 10 ohm)

As the result, RS-485 output signal level is reduced.

Based on TI’s failure analysis, output pin(#7) and GND are shorted.

We suspect that ESD protection cell in THV1450 is broken by any reason.

 

As countermeasure for this issue, we applied below items.

1)Connect GND between host PC and product in apparel to RS-485.

We have a doubt ESD or GND line noise based on voltage gap between them.

(Power is supplied from host PC system, so we made them common.)

2)To avoid IC broken by hot swap, added discharge resister between RS-485 signal lines and GND.

3)Confirm all frame GNDs are connected to earth.

 

But still now, same failure never gone away.

 

Is there any possibility that cause like this issue?

Any idea is appreciated.

Best regards.

  • 0
    Guru 243660 points

    Do you have any information about what ESD/voltage spikes can be expected? How electrically noisy is your environment?

    Do you have any external protection components (diodes, TVS)?

  • 0 in reply to Clemens Ladisch
    TI__Guru 60202 points

    Takiguchi-san,

    Along with Clemens questions, I have some of my own:

    • How many devices is this happening?
    • Is it always the same failure, a short between pin 7 and GND?
    • Is it possible to share a block diagram, schematic, and/or layout of the board?

    Regards,

    Eric Hackett 

  • 0 in reply to Clemens Ladisch
    Prodigy 250 points

    Temp.pdf

    Thank you for your reply.

    For ESD, we already applied standard ESD counter measure ESD strap etc. So we suspect no chance to cause ESD at production line.

    Regarding spike, noise, I think there is no chance.

    But for electrical noise, there are some constant temperature chambers around production line.

    So now we have a doubt chamber noise via frame ground.

    Abut component and detail information, please refer to attached file.

    Failure rate is very unstable. Until now, almost 30pcs NG products were found. Broken pin is #7 or #6 (D+/D- of RS-485)

     

    Best regards

  • 0 in reply to Junji Takiguchi
    TI__Guru 60202 points

    Junji,

    Thanks for all of this information, the reason Clemens and I asked about ESD and other high voltage countermeasures and conditions is because this kind of failure, a bus short to GND, is a typically failure signature. And with it happening so frequently on so many devices, my assumption is that there is something in your system causing electrical overstress on the bus pins. Why do you think there is no chance for a voltage spike or excessive noise?

    Is it possible to observe the bus with an oscilloscope while operating to detect any high voltage spikes? 

    Regards,

    Eric Hackett