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AM26LV31E: AM26LV31E RS485

mor ge
Prodigy 110 points

Part Number: AM26LV31E

Hi,

I am designing a new design and have chosen to use with AM26LV31EIRGYR component for:

  • 3 X RS422 outputs
  • 1 X RS485 output

 

Is the component compatible for use with the RS485 standard too?

 

Regards,

Mor

  • 0
    Guru 321450 points

    The electrical characteristics are guaranteed only for a RS-422 load (at least 2 V over 100 Ω).

    An RS-485 driver would be required to output at least 1.5 V over a 54 Ω load. It is likely that the AM26LV31E can do this, but there is no guarantee. However, differential receivers can work with at most 0.2 V, so in the worst case, you have just a reduced noise margin.

    RS-422 and RS-485 have slightly different limits for bus voltages.

  • 0
    TI__Guru 58358 points

    Hi Mor,

    Clemens said it perfectly. AM26LV31E is designed for the RS422 standard. This differential line driver is guaranteed to output a differential voltage of +/- 2V across a 100 ohm load. RS485 drivers are designed to drive a differential output of +/- 1.5V across 54 ohm load. It is likely the case that AM26LV31E can drive this type of load, but no guarantee.

    RS422 or RS485 standardized receivers have a input sensitivity of +/- 200mV to determine if signal is HIGH or LOW. Like Clemens stated, you will have reduced noise margin using a RS422 driver for RS485 application. 

    Clemens stated that RS422 and RS485 standards have different limits for bus voltages. This is due to common mode range. 

    Max Common-Mode Voltage RS422: -7V to +7V

    Max Common-Mode Voltage RS485: -7V to +12V

    RS485 devices also have wider data rate ranges up to 50 Mbps, can support more devices on the same bus, and receivers have higher input resistance. 

    Regards,

    Tyler