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Original question:

ISOW7841: output failure

ISOW7841: Output failure

Moritz Gedig
Prodigy 10 points
Part Number: ISOW7841
Other Parts Discussed in Thread: ISOW7741, ISOW1432

Like in these posts:


https://e2e.ti.com/support/isolation-group/isolation/f/isolation-forum/884225/isow7841-isow7841dwer-damage-question


https://e2e.ti.com/support/isolation-group/isolation/f/isolation-forum/1034264/isow7841-output-failure


https://e2e.ti.com/support/isolation-group/isolation/f/isolation-forum/898586/isow7841-high-rate-of-part-failures


https://e2e.ti.com/support/isolation-group/isolation/f/isolation-forum/667089/isow7841-isow7841-output-voltage-problem


I have the issue that multiple ISOW7841 (DWE) keep going low resistance on the power output. The power draw goes up, the voltage down.
I can not find any reason for this damage/behaviour.
I am unable to find the passage about rise time on the primary side in the current datasheet. As in the other post my application has low current demand. Actually the IC that breaks the most often is the one with the least demand on it. It just make no sense. Sure the IC doesn't need a minimum load?
The output capacitance is 47uF+100nF+100nF. The load is a TI THVD1450D in receive mode. DE is low.
I will supply any details in written form or draw sketches.

[defect broken]

  • 0
    TI__Guru 54155 points

    Hi Moritz,

    Thank you for reaching out and sorry to hear about the issue.

    The ISOW7841 device manufactured in and prior to 2020 needed some additional guidelines to be followed to operate normal in all test conditions. Not following the guidelines could lead to device output going to overvoltage and causing permanent damage, especially when the device is used in noisy environment. It is important to follow the guidelines specified in datasheet version that was available in and prior to year 2020.

    The devices manufactured from 2021 onward do not require to follow these additional guidelines, just the standard guidelines provided in current datasheet are sufficient. Please see below a screenshot of the guidelines that was included in the datasheets in and prior years of 2020. Current datasheet doesn't have this paragraph specified as these are not needed for the devices that are being manufactured currently.

    Please do share the images of device samples so that I can read the top markings on device to determine when they were manufactured and confirm to you accordingly. You can also order new samples from TI website and test to confirm that the issue doesn't exist.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 10 points

    We are collecting the data. We kept some of the defective ICs and should have some record on shipments. Our environment is indeed noisy which is part of the reason why we use the isolators.

  • 0 in reply to Koteshwar Rao
    Prodigy 10 points

    It does appear that our stock is from mid 2019 (DC 1911) and entered our inventory in early 2020.  But there was also some DC 1832 that arrived in April 2019.

    Do you need the code on the back or the front of the package? The front says: 93AKDHT

    There are too many codes here, one is: 9197784TW9

  • +1 in reply to Moritz Gedig
    TI__Guru 54155 points

    Hi Moritz,

    Thank you for sharing additional information and confirming that the samples are from 2018 and 2019.

    Moritz Gedig said:

    The front says: 93AKDHT

    I needed the top marking of device, this is the correct code that I was looking for. This is a 7 character Lot Trace Code (Code) where the first two digits indicate year and month they are manufactured. 93 indicates 2019 March.

    Since the samples you have are from 2018 and 2019, please consider using the newer samples for your design to avoid following additional guidelines. If you prefer to use the older samples, please consider following the additional guidelines from the snippet I shared in my previous response. Please also share me the schematic so that I can review and confirm if the design is okay.

    If this is a new design, we recommend that you consider our newer 2nd generation ISOW device, ISOW7741 which offers significantly improved overall performance. Let me know if you have any further questions, thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 10 points

    Thank you

    "please consider using the newer samples for your design to avoid following additional guidelines."

    We will liquidate our stock and use newer.

    "If this is a new design, we recommend that you consider our newer 2nd generation ISOW device, ISOW7741 which offers significantly improved overall performance."

    It would be sufficient if they didn't fail all the time. There should have been a recall.

    What is the best option:  ISOW774x, ISOW784x  or  ADUM540x, ADUM642x  ? Or do I need to google for anecdotal hints that these might have issues too?

    If I order or you send me some of every type I could put them to the test in my hardware.


    The 5V come from a DCDC Buck regulator. What would you need to know about it?

  • 0 in reply to Moritz Gedig
    TI__Guru 54155 points

    Hi Moritz,

    Apologies for the inconvenience again.

    Moritz Gedig said:
    It would be sufficient if they didn't fail all the time. There should have been a recall.

    Since ISOW7741 is a second-generation device, all the learning from first-generation family have been incorporated. It also has been 3 years since ISOW7741 has been released and we haven't heard any customers report any failure concerns.

    Moritz Gedig said:
    What is the best option:  ISOW774x, ISOW784x  or  ADUM540x, ADUM642x  ? Or do I need to google for anecdotal hints that these might have issues too?

    ISOW774x would be the best option for all new designs as this device offers significant performance improvement from previous generation and also has all the learning incorporated into it.

    Moritz Gedig said:
    If I order or you send me some of every type I could put them to the test in my hardware.

    The device samples can be ordered for free from the website. If you would like me to order it for you, please help me with shipping address, name and contact information of the person it is being shipped to. Please include work email and phone number.

    Thank you for sharing the schematic. Since you are using the isolator to isolate RS-485 bus, you could also consider ISOW1432 which integrates ISOW774x with an RS-485 transceiver. Please note that ISOW1432 supports a maximum datarate of 12Mbps. Thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 10 points
    Koteshwar Rao said:
    you are using the isolator to isolate RS-485 bus, you could also consider ISOW1432 which integrates ISOW774x with an RS-485 transceiver.

    Good advice. Thanks