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SN65HVD75: The absolute maximum rating of supply voltage has been changed

Genius 4305 points

Replies: 8

Views: 218

Part Number: SN65HVD75

Hello support team,

Regarding SN65HVD75, we received a PCN that the absolute maximum ratings of Supply voltage (VCC) and R pin was changed from 5.5 V to 3.6 V.

Our customer uses the combination of ISOW7821 and SN65HVD75 on his circuit.
These devices are already in the design-in state to the customer.
In the customer's circuit, the supply voltage of ISOW7821 is 3.3 V.
Looking at the specifications of ISOW7821, the maximum value of VISO is 3.58 V when the supply voltage is 3.3 V ± 10%.
It seems that there is no margin against this absolute maximum rating of SN65HVD75 of which is 3.6 V.

[Questions]
1. Although the absolute maximum rating has been changed, are there any problem if the customer continues to use the combination of these devices?

2. Do you have any experience with this combination?

3. If the supply voltage of the ISOW7821 exceeds 3.3 V + 10%, is there a possibility that the voltage of VISO exceeds 3.6 V?

4. If the supply voltage of the ISOW7821 is limited to the range of 3.3 V ± 5%, will the maximum voltage of VISO be lower than 3.58 V?

We think that we need to give the customer some advice.

Sincerely,
M. Tachibana

  • Genius 10615 points
    Tachibana-san,

    From what you described, I think the combination should still work. Surely it would be better if we had better control on the supply of SN65HVD75. The experts on isolation products will address your concerns about ISOW7821.

    Regards,
    Hao
  • In reply to Hao L:

    Hi Tachibana-san,

    Thank you for posting these questions on E2E. Please allow the Isolation group 1-2 days to respond concerning the questions on ISOW7821.


    Thank you for your time,
    Manuel Chavez
  • In reply to Manuel Chavez:

    Hi Hao-san and Manuel-san,

    Thanks for your comment.
    I'm waiting for information on ISOW7821.

    Sincerely,
    M. Tachibana
  • In reply to Masanori Tachibana:

    Hi Tachibana-san,

    Sorry for the delay in answering your question. Please see my answers to your questions below:

    3. If the supply voltage of the ISOW7821 exceeds 3.3 V + 10%, is there a possibility that the voltage of VISO exceeds 3.6 V?.

    The datasheet max VISO of 3.58 for Vcc of 3.3V +/-10%. If Vcc exceeds that I cannot guarantee that VISO would not also exceed 3.6V. I would expect that if it was slightly higher or lower that it would not exceed it - but you would have to test that in your system across temperature and several different units to ensure it.

    4. If the supply voltage of the ISOW7821 is limited to the range of 3.3 V ± 5%, will the maximum voltage of VISO be lower than 3.58 V?

    The datasheet max VISO  is 3.58V for Vcc of 3.3V +/-10%. So for Vcc of 3.3 V ± 5%, VISO would not exceed 3.6 V (guaranteed by the datasheet) and therefore would not damage the SN65HVD75 with an abs max of 3.6V. We cannot guarantee that the maximum would be lower than 3.58V for a Vcc of 3.3 V ± 5%.

    Do you have any further questions?

    Best regards, 

    Dan

  • In reply to Dan Kisling:

    Hi Dan-san,

    Thank you for teaching me your view.
    From described in the datasheet, I understand that your view is correct.

    However, the absolute maximum rating of SN65HVD75 is 3.6 V comparing to the maximum VISO value of ISOW7821 which is 3.58 V, and the margin between them is only 20 mV. I think it is too small.
    If noise or overshoot is superimposed on VCC or RIN even a little, I think there is a possibility of exceeding the absolute maximum rating which is 3.6V.
    Therefore, I would like to know how to lower the maximum value of VISO of ISOW7821 because I want to get as much margin as possible.
    If you have any good ideas, please let me know.

    Sincerely,
    M. Tachibana

  • In reply to Masanori Tachibana:

    Hi Tachibana-san,

    I understand your concern on not having enough margin between ISOW VISO output and SN65HVD75 VCC input. The primary reason for VISO output voltage variation is due to the variation in an internal reference voltage that sets the output to a predefined voltage. Though output voltage does have a dependency on input voltage, it is not very significant. Hence like Dan mentioned, bringing down input voltage variation to 5% doesn't have much of an impact in reducing VISO output voltage variation. I am afraid there isn't a way to reduce output voltage without adding a post-regulator.

    If your concern is about short duration transients or overshoot at VISO due to external factors, I believe such transients (if short in duration) are handled by ESD protection on VCC of SN65HVD75. Perhaps Hao L can confirm on this.

    Alternatively, customer can improve this using external components. Setting VISO to 5V and using an LDO to bring it down to 3.3V can bring down LDO the output to a much lower variation. This approach requires a voltage translator to be used between ISOW data channels and SN65HVD75 connections.

    I hope the above options help customer meet their requirements. Thanks.


    Regards,
    Koteshwar Rao
  • In reply to Koteshwar Rao:

    Hello Tachibana-san,

    In addition to the comments made by the Isolation experts above, I would also like to clarify that the SN65HVD75 will not be immediately damaged by any voltage above 3.6 V. Rather, the absolute maximum limit here indicates the voltage above which the lifetime reliability of the device may degrade. Because this is a long-term concern, the degradation would only be significant if the device were operated >3.6 V for a substantial proportion of its life. Short-duration overshoots between 3.6 V and 5.5 V would have a negligible impact on the operation of the device or its long-term reliability.

    Max
  • In reply to Max Robertson:

    Hi all,

    Thank you for giving me a lot of advice.
    I understood that VISO voltage range of ISOW7821 can not be controlled with supply voltage of it.
    I will consider proposing a circuit to lower the voltage between VISO of ISOW7821 and VCC of SN65HVD75, or will consider proposing another device such as THVD1450 which is pin compatible with SN65HVD75.

    Sincerely,
    M. Tachibana

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