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SN65HVD72: Series resistor burning issue on RS-485 bus - SN65HVD72DR

Aravind .R
Genius 3175 points
Part Number: SN65HVD72
Other Parts Discussed in Thread: THVD1410, THVD1451, THVD1450, SN65HVD1786

Dear All,

one of my customer using SN65HVD72DR in their 1kW Battery Management system, customer facing issue in which series resistor on RS-485 bus is getting burnt, we are thinking it might be due to higher common mode voltage when low side cutoff happens for battery pack, schematics attached, look forward for your feedback/suggestions to resolve this issue.

Also please suggest  good RS-485 device with common mode voltage greater than 20V

Rgds,

Aravind. 

  • 0
    TI__Expert 3770 points

    Hi Aravind,

    thanks for including the schematic. It helps to understand your problem even though not entirely.

    - Regarding the resistors burning I believe you're talking about resistors R75 and R78; do you know what's their power rating? It would be ideal for me to know which voltages do you measure across the resistors. If you have the actual board from the customer, it would be great to recreate the issue and try different solutions. As a first suggestion, I would try to lower the value of the two resistors and see if the problem occurs, if not eliminate them completely. Otherwise some TVS diodes could be helpful if there are transients causing the problem; but the diodes would affect the communication in case they clamp.

    - Unfortunately we don't have specific devices that work with VCC=3.3V and VCM up to+20V. If your customer wants to use only 3.3V the maximum common mode range that we do have is -15/+15. These are the THVD1410, THVD1450 and THVD1451.

    If they are willing to switch to 5V power supply, in this case we do have transceivers supporting up to -20/+25V of common mode. These would be the SN65HVD2x family or the SN65HVD1786 and SN65HVD87.

    Please let me know if you have more details on the measurements discussed above.

    Regards,

    Adrian