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TCA9517: I2C over cable + PCB

user5992354
Prodigy 30 points
Part Number: TCA9517
Other Parts Discussed in Thread: PCA9517, , , P82B715, P82B96

Hi there,

I'd like to control a slave Device through I2C (100kHz) over a 1m length distance, as depicted here below : 

Is the PCA9517 a good choice, and do I need to use two parts at both sides ( one in board 2 and another onto board 4) ?

Thank you.

Paulo. 

  • 0
    TI__Guru 60850 points
    Hey Paulo,

    May I know what Vcc you intend to use?

    "do I need to use two parts at both sides"
    Having two on both sides is a good idea because it will buffer out the capacitance/inductance of the cable from the I2C slave and master.

    On concern about this is that B sides of TCA9517 should not be connected together. For your application A to A should be connected.

    "Is the PCA9517 a good choice"
    I think TCA9517A would be a good pick for this application.

    Thanks,
    -Bobby
  • 0 in reply to BOBBY
    Prodigy 30 points

    Hi Bobby,

    VCC is 3V3. So B side to A Side right ?

    I also noticed that the P82B715 could fit within the same configuration, but 3V3 seems too low regarding the recommended operating conditions.


    It is said that the P82B715 is a device for buffering highly capacitive I 2C bus systems, up to 3000nF !


    What about the I2C frequency with such a capacitive bus ? Could it goes up to 400kHz ?

    Regards.

  • 0 in reply to user5992354
    TI__Guru 60850 points
    "VCC is 3V3. So B side to A Side right ?"
    B to A is okay. But for cable transmission I would have both A sides face the cable.

    "It is said that the P82B715 is a device for buffering highly capacitive I 2C bus systems, up to 3000nF !"
    It can technically handle 3000pF or 3nF. This device is not actually a buffer in the sense it redrives the signal.

    We also have P82B96 which may fit in your application as it can handle 4000pF of capacitance.

    I think if you are running at 3.3V and 100kHz, the TCA9517A would be a good solution.

    "What about the I2C frequency with such a capacitive bus ? Could it goes up to 400kHz ?"
    At 3000nF (3uF) it probably wouldn't be possible. At 3000pF or 4000pF you could achieve 400kHz communication with P82B96. I don't think you need the P82B96 for this application as that device was meant for much longer cables.

    May I know what application/end equipment you are working on? I am interested to know if this is something that is going to be used in a factory automation/power grid environment. If so then we may want to think of a different approach as EMI in the environment may be a concern. If so, you may want to use I2C to CAN: www.ti.com/.../TIDA-060013

    Thanks,
    -Bobby
  • 0 in reply to BOBBY
    Prodigy 30 points

    Hi Bobby,

    actually I need to drive relays that are 1 meter max away from the I2C master in a lab environment. 

    I'll use the TCA9517A.

    Thank you for your help.

    Paulo. 

  • 0 in reply to user5992354
    TI__Guru 60850 points

    Hey Paulo,

    Glad to help, when you get to the schematic/layout phase of your project I can give it a quick look to see if there any silly mistakes/corrections that should be made. Feel free to send it to me via email as this is a public forum.

    -Bobby

    Email:

    duynguyen@ti.com