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ISO3082: Schematic Review

Kruti Panchasara
Prodigy 20 points
Part Number: ISO3082
Other Parts Discussed in Thread: ISO1500, ISO1410

Hello, 

we have designed the schematic as per datasheet of ISO3082 . We request you to verify it so we can go ahead with Layout design.

RS485.pdf

  • 0
    TI__Mastermind 49445 points

    Hi Kruti,

    Thanks for reaching out and sharing the schematic for review.
    I have reviewed the schematic, I have the following comments.

    1. I see that there two series resistors used on RS-485 bus pins R97 and R98 that I think are valued 10kΩ. Such large values can significantly impact the datarate and timing specifications that can be achieved. We recommend them to be of 10Ω for protection against EMI transients.
    2. I see that there are LEDs connected to the I/O pins on Side1 (VCC1 side). I am not sure about the minimum current requirement for these diodes to be turned on, but do note that the output pin number 3 (R) on Side1 should only be allowed to sink a maximum of 2mA into the device for 3.3V VCC1. The maximum recommended sinking current for 5V VCC1 is 4mA. This is explicitly not stated in this datasheet but is a common spec across most of TI digital isolators.
    3. I only see a 10µF capacitor on VCC2, we recommend that an additional 0.1µF capacitor is used on VCC2 and is placed as close as possible to the pins. Please check datasheet layout recommendations and example PCB layout.
    4. ISO3082 is one of older RS-485 family of devices, our latest devices ISO1410 and ISO1500 offer much better performance compared to ISO3082. Hence, we recommend these devices to be used for better overall performance including EMC.


    Regards,
    Koteshwar Rao