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RS485 half-duplex repeater using ISO15

Gaston Schelotto
Expert 2840 points

Hello,

I've taken a look at the Data-rate independent half-duplex repeater design for RS-485 and I'd like to know where is Cs in the circuit schematic.

Last question, is it feasible to use this 3.3V repeater in a 5V bus?

Regards,
gaston

  • 0
    TI__Mastermind 28265 points

    Gaston,

    Cs is supposed to buffer the 3.3V power supply. For some reason reason it got lost, and YES you can use a 3V repater in a 5V network. RS-485 receivers only look at the differential bus signal and not with regards to Gnd or Vcc. I also havea 5V single-isolated version in the attachement.

    Let me know how you like it. Cheers, Thomas 

    Single Isolated Half-Duplex Repeater.pdf
  • 0 in reply to Thomas Kugelstadt
    Expert 2840 points

    Thomas,

    Thanks for the clarification. The pdf in the attachment is quite different from the original application note. What was the motivation for this change?

    • Better performance?
    • Improve efficiency?
    • Other?

    At a first glance, the original approach separates the buses with a rating insulation of 2 x 2500 VRMS whereas the 5V design has a separation of 2500 VRMS.

    Regards,
    gaston

  • 0 in reply to Thomas Kugelstadt
    Expert 2840 points

    Thomas,

    I've made some prototypes using your first approach. They are intended for training purposes (not commercial) so I hope there is no problem with licenses or rights. The pleasant surprise is that it worked at the first time -with no errors-, somewhat unusual in electronics. For this reason let me share your design come true in next slides (in Spanish so far)

    PCB design using KiCad

    Regards,
    gaston