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

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

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

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