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SN65HVD22 Powerline Communication

Murat ULUYILMAZ
Prodigy 30 points
Other Parts Discussed in Thread: SN65HVD22, SN65HVD96

Hi ;

I am working on a network with Modbus RTU. in my design I used SN65HVD22 because of 24v A-B and 240 Nodes and 1000mt . This is a great Tranciever . I manage to communicate with 4 wire A-B and Vcc + Gnd .

Now I am trying to use Power on data . 2wires with data and power. There is a document of SN65HVD96 that describes how to do it. But can I do that with my SN65HVD22 and how could ı calculate the capacitors and inductors value . Is there a tool , calculator or formula to do that. 

My slaves MCU 1mhz , 4800Baudrate and line power is 24v . 

Thanks .

Regards

Murat ..

  • 0
    TI__Intellectual 905 points

    Hello Murat,


    welcome to the forum! I guess the document you mentioned regarding the SN65HVD96 is this one:

    http://www.ti.com/lit/an/slla336/slla336.pdf

    There is also another TI design, to evaluate power over RS-485:

    http://www.ti.com/lit/ug/tidu993/tidu993.pdf

    Could you please explain what you understand with 24 V line power understand? Regarding the Inductor size, I'll try to come up with an answer asap.


    Regards,

    Till

  • 0 in reply to Till-Jonas Ostermann
    Prodigy 30 points
    Hello Till ;

    I also checked tidu993.pdf .

    Simply I need to use this Power on data structure on my own designed I/O cards . Can not use an external modem or a card. So I got sensor cards and output cards . The output cards needs 24v to drive some interface. İnput cards are sensor cards which works with 5v with LDO . I am using Modbus RTU 485 protocol with tranciever sn65hvd22 . I need to communicate and powerup my cards over 2 wire. At my slaves the data and power will be on 2 wire line.

    So I should use exact same design on A and B pins as shown at

    www.ti.com/.../slla336.pdf

    And if I am not wrong on slla336 the values of C and L s are only for example . Somewhere I have readed the V , MCU speed and baudrate values are needed to calculate C and L values .
    Thanks for reply
  • 0 in reply to Murat ULUYILMAZ
    TI__Prodigy 740 points

    Hello Murat,

    did I get you right, you want to generate the 5V for your slave card from 24V with an LDO transmitted over the bus lines?
    If so the LDO will help you to filter the signal as well, but please take into account that dependent on your current consumption you might dissipate a lot of heat there.

    Regarding the filter we have a low pass transfer function from bus line to power line. Dependent on the values you choose for L and C it looks similar to the following plot:

    To calculate appropriate values for L and C you should know:

    1. The maximum ripple allowed after the filter. This might be related to the LDO you plan to use, the input capacitor of the LDO, etc.

    2. The frequencies you want to attenuate. I am not familiar with the Modbus protocol, but you should know the lowest frequency you need to "block". An easy way might be to do a fourier analysis of your signal with an oscilloscope and check the higher energy frequencies contained. The "main" frequency in your case should be 9.6 kHz for a baud rate of 4.8 kbaud, but with  series of ones and zeros you will get other frequencies as well (and it is no sine of course, but those harmonics will be of higher frequency).

    You can calculate the -3dB roll-off frequency using the following formula:

    Also be aware of the current rating of your inductors, those will conduct all your current to your slave boards.

    Best regards,
    Christian

  • 0 in reply to Christian Klickow
    Prodigy 30 points
    Hello Mr. KLICKOW ,

    Thank you for reply . This information is really usefull for me to understand the subject . I am starting to try to find out the Capacitors on powerline . if I get some results I ll share here . If I could manage to communicate my slave and master devices with SN65HVD22 on 2 wire power , passing the tests we ll order at least 12000 pieces for start . So this will be the best tranciever for our project I think.

    Best Regards .

    Murat ULUYILMAZ
  • 0 in reply to Murat ULUYILMAZ
    TI__Prodigy 740 points

    Hello Mr. ULUYILMAZ,

    great news you plan to use our SN65HVD22 in your project. I would like to let the product experts comment whether this is the best fit for your application, but I am sure you have made a good choice. Please share your results as you move on and we will do our best to support you through this forum.

    Best regards,
    Christian