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SN65HVD251DR Rx Output Pin Failed Why?

Ed Wilinski
Prodigy 120 points
Other Parts Discussed in Thread: SN65HVD251

We're using the SN65HVD251DR as an CAN interface on our Battery Monitor device. We had a failure where the Rx pin on the logic side failed.

The Rx pin is connected to 390ohm  resistor to the Cathode of the LED of a 6N137SM optocoupler.

The Anode of the LED is connected to the output of a TI part# DCP010505BP-U/700 DC/DC isolator which is not outputting +5V but 6.1V probably due to not being heavily loaded.

The SN65HVD251 is also powered by the DCP010505BP-U700 so its getting 6.1V on its Vcc pin could this cause a failure on the Rx pin?

Thanks,

Ed

  • 0
    TI__Guru 62910 points
    Hi Ed,

    The 6.1 V on VCC shouldn't be damaging the SN65HVD251; that device will survive up to at least 7 V on VCC. One potential issue, though, is the current rating of the receiver output pin. Per the "Absolute Maximum Ratings" table in the HVD251 datasheet, the current flowing into or out of the R pin should be less than 10 mA. With a 1.45-V forward voltage in the optocoupler, a pull-up voltage of 6.1 V, and a series resistance of 390 Ohms, the receive pin current would be ~12 mA. I recommend either increasing the series resistance value or dropping the voltage to ~5 V in order to safely stay within the pin's current rating.

    Regards,
    Max