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ISO3082: Isolated RS-485 with TTL output

Srikanth Yakkala
Prodigy 20 points
Part Number: ISO3082


Hi ,

I am very beginner in designing area. I would like to design a Rs485 to read the status of the FPGA for diagnostic purposes. 

For that I selected Isolated Rs-485 IC but I need TTL output to read the RS-485 data.

Please recommend me the appropriate IC for this application or reference diagram to shift the RS 485 output level to TTL.

Thank you in advance

Best regards

Srikanth

  • 0
    TI__Expert 6195 points

    Hi Srikanth,

    Thanks for posting your question on E2E!

    At first glance, I think the ISO3082 should interface with TTL without any additional parts. Take a look at page 8 of the ISO3082 datasheet that I've marked up below. 

    Typically I see TTL specified at <0.7V for low thresholds and >2V for high thresholds. The ISO3082 would meet these specs for both 5V and 3.3V operation. 

    Perhaps the threshold specifications are different for your system though. If you provide the microcontroller part number and the supply for side 1 of the ISO3082 and the microcontroller I would be happy to take a look and see if this will work. 

    Best regards, 

    Dan

  • 0 in reply to Dan Kisling
    Prodigy 20 points
    Thank for the reply. I am only using the driver in ISO3082.

    Does the driver in ISO3082 can give the TTL output?

    I need RS485 to read the status of max 10 FPGA every 1 sec. To do this, I am using UART protocol in FPGA with RS5485 as interface to read it. The output of the RS485(Driver output) should be in TT logic output level.

    Thank you.
  • 0 in reply to Srikanth Yakkala
    TI__Expert 6195 points

    Hi Srikanth,

    To clarify, you are asking about the RX pin interfacing with the FPGA, correct? Or are you talking about bus side of the ISO3082. 

    According to the ISO3082 and the MAX 10 FPGA datasheet this should be fine if we are talking about RX. 

    I've marked up page 19 of the MAX 10 FPGA datasheet:

    VIL max is 0.8V. VOL max of the ISO3082 therefore must therefore be <0.8. It meets this spec as the ISO3082 VOL max spec is 0.4V. 

    VIH min is 1.7V. VOH min of the ISO3082 therefore must be >1.7V. It meets this spec as the ISO3082 VOH min spec is Vcc-0.4V (3.3V-0.4V=2.9V). 

    Best regards, 

    Dan