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any solution for the hot swap function for the communication interface?

Aki Li
Genius 9885 points
Other Parts Discussed in Thread: TCA9511A

My customer is asking whether there are suggested solution to achieve hot swap for the communication interface, like SPI and CAN. In their system, there are multiple communication cards, so they are afraid the potential spikes/noise when connecting different boards. Actually I am not sure whether it is necessary to consider the hot swap solution in such case. Could you please help share some guidance? Thank you.

  • 0
    TI__Guru 74322 points

    Aki,

    Thanks for bringing this question to E2E. This request is a bit vague, can you give more details about the requirements of the interface or application?

    • What exactly is the end equipment?
    • Data rate?
    • Differential or single-ended?
    • Physical length of communication

    This sounds like a fit for I2C depending on the physical distance of the communication bus, but we'll need a bit more information before we can suggest an interface.

    Regards,

  • 0 in reply to Eric Hackett
    TI__Genius 9885 points

    Hi Eric,

    They were designed communication boards for UPS. Please check the below feedback:

    Data rate: CAN 1M bit/s(MAX)   SPI 400k bit/s  

    Differential or single-ended: some  differential and  some single-ended.

    Physical length of communication: CAN-50 meters,  other-2 meters

    It seemed that I2C interface can use TCA9511A for the hot swap, but I am not clear whether it is necessary for other interface and what solutions to suggest. 

  • 0 in reply to Aki Li
    TI__Guru* 76131 points

    Aki,

    In the I2C domain, the SDA (sometimes SCL) are bidirectional and the concern is that when you hotplug a unpowered card into an live bus, the initial in rush current could cause a bad power on reset (resulting in a stuck bus) or also cause signal integrity issues to the main bus during the insertion. 

    With a unidirectional communication (like SPI) or point to point communication, this doesn't seem like a concern you would need to worry about since you aren't going to be worried about a stuck bus in a unidirectional protocol. Maybe you would want to have some kind of transient voltage protection in the case that you insert a unpowered card and see a large transient on the unpowered side which could cause damage to the devices. I'm not an expert on the CAN devices but I believe they have designed in some EFT protection so 'hot insertion' voltage transients may be less of a worry. One approach could be for a SPI case, you could place a unidirectional level shifter on the external card to protect the downstream devices from being damaged by a transient voltage on the signal path (you would let the level shifter take the brunt of the transients though). In that kind of set up, I would use some RC circuit on the enable pin to delay turning on the level shifter until after insertion occurs (should happen in microsecond range so use a millisecond RC). The other approach may be to use a TVS diode.

    -Bobby