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ISO7742: ISO7742 Fail Issue

Part Number: ISO7742
Other Parts Discussed in Thread: TPD1E10B06, ISO7741

Please reference QEM-CCR-1809-00743 FA report figure 8, Customer like to know which area part will be damage, RD need to know it for Solve hidden problems, thanks !

  • Hi James!

    Thanks for posting your question on E2E. Pin 12 on the ISO7742 is an input on side 2, so damage may be to ESD diodes due to an overvoltage event with respect to Vcc2.

    I will ask a designer for clarity on the die, and in the meantime what is the device's full part number? Does the customer have known transients in the system exceeding Vcc2 + 0.5V?


    Best,
    Manuel Chavez
  • Hi Manuel ,

    ISO7742DW

    Best
    James Su
  • James,

    According to our FA report and quality team there was damage to the device's ESD cell. Pins 12 and 16 shorted to ground.

    I hope this is helpful! Have a great weekend.


    Respectfully,
    Manuel Chavez
  • Hi Manuel ,

    ESD cell local in where, please point in out by pic, thanks !

    Best
    James Su
  • Hi James,

    I cannot point out a specific component or connection in the image above, but the metal is melted/ burnt. ESD damage to ISO7742 and many other semiconductor devices can be prevented by using external TVS diodes, like the TPD1E10B06, to pull I/O or supply pins to ground.

    Additionally PTC fuses may be placed in series with the pin to protect a device and TVS from damage during longer over-voltage events. How would your customer like to prevent this damage from occurring again? We want to help with constructing this while details about which part of the ESD cell is burnt are not beneficial to the solution.


    Thank you for your time,
    Manuel Chavez
  • Hi Manuel ,

    I can understand I/O fail condition now, But customer have new fail unit and only Vcc pin short to Ground pin, please help to Explanation it, thanks !

    Best
    James Su
  • James,

    Damage to ESD cells is caused by over-voltage events. The customer may be damaging devices by unintentionally exposing them to voltages that exceed datasheet ratings for each pin.

    ESD damage may come from a brief discharge if the device is not being handled in an ESD safe work area or from transient voltages.

    If you and your customer are willing to share a schematic, I can review and make recommendations to help prevent this damage in future devices. The best approach is to know all voltages the device is exposed to are within datasheet specs, especially absolute maximums.


    I will await your response.


    Best,
    Manuel Chavez
  • HI Manuel,

    schematic , fyi

    PCBA1 use C2000 and Through ISO7741 to PCBA2 ST MCU Interface board, then PCB trace around 25cm and 10cm Cable.

    B/R James

  • Thanks James!

    To prevent transient voltages from damaging the Vcc pins 5V TVS diode clamps can be used in parallel with CP31 and CP44. This is the preferred solution. Zener diode clamps may also be used, but TVS diodes respond quicker for fast transients.

    Below are two general comments on the schematic:

    1. It is unusual for enable pins to be left floating. They should be pulled up to Vcc with a 4.7kOhm resistor if output enable is desired or pulled low to GND to make the output pins on each side high impedance.

    2. a 1uF capacitor can help the ISO device respond to sudden load changes in addition to  the 0.1uF caps on Vcc. A sketch of this solution is pictured below:



    Is the customer finding these failed devices in tests or randomly during normal operation?

    Please respond if this is helpful.


    Thank you for your time,
    Manuel Chavez

  • James,

    Just following up with more information, the TVS diodes shown in the previous post are bidirectional. Uni-directional TVS diodes are available like ON's 5.5V ESDM1131. Uni- and bidirectional TVS diodes achieve the same protection goal here, yielding more choices for the customer. This is worth considering since bidirectional diodes may be overkill for this application.


    Thank you,
    Manuel Chavez
  • Hi James,

    It has been a couple weeks since this thread was active. I am going to assume the customer issue has been taken care of; if this is not the case please reply to this thread or ask a new question.

    Thank you for posting to the E2E forums.


    Respectfully,
    Manuel Chavez
  • Thanks. We still  get some stress from customer site about this failure issue since we doesn't explain it more detail.

    Could you point out that where the circuitry/ESD I/O diode are possibly damaged on the die depends on the FA report? customer would like to know more detail to investigate it and prevent it in the future. Please advice. thanks.

  • Brian,

    The short answer is more details are not needed to investigate and prevent ESD damage; the device pins only need to be protected from excessive voltages. I will follow up via email.


    Thank you,
    Manuel Chavez