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TCA4311A: Hot Swap Issue

Part Number: TCA4311A
Other Parts Discussed in Thread: SN74CBT6800A, SN74CBTS6800, , SN74CBTLV3384

Hello,

                             Figure 12 show the schematics for pin same length, Figure 11 show the schematics show pin different pin length. But why Figure 11 needs a hot swap power supply but Figure 12 don't need?

                              Another question, customer hope has logic solution for 8bit or 16 bit for signal hot swap (maybe for UART/I2C/IO..etc) . Do we have support hot swap function buffer to customer? Are SN74CBT6800A /SN74CBTS6800  ok for this application? Thank you. 

                  

BR

Patrick

  • Hello Patrick,
    I am assuming that figure 11 is the second schematic.

    Figure 11, has a DC-DC converter which means is has a HUGE amount of input capacitance. Imagine that you were to take a 12V supply and connect it directly to a discharged caps of the DC-DC converter. You would have a HUGE inrush current due to dv/dt. That means you will also have the same huge current go through the connections which have inductance. That would mean you would have a huge overshoot which could damage parts. Therefore, a Hot Swap part controls the current going into the input caps such that it is a slow ramp and there is not a large inrush current and no voltage overshoot due to inductive ringing.

    Figure 12 is connecting the supply, Vcc, that has a lot of capacitance to a really small input cap (0.01uF). This means only a small amount or inrush current relative to what is seen at the input of a DC-DC converter. Therefore no need to place protection in front of it.
     
    Hope that explains your first question.

    Second question. I am not quite sure what you are asking here. Is this figure 11's bus switch? Can you elaborate on the questions and explain what exactly they are trying to do and what they have concerns about?
    -Francis Houde

  • Hello Francis

    Thank you for your reply. For second question, I just know if SN74CBT6800A /SN74CBTS6800 support hot swap function or not. If can't, has any 8bit or 16 bit buffer logic solution can support hot swap as TCA4311A? Thank you.


    BR
    Patrick
  • Hello Patrick,
    I am not sure you need the exact same features that the TCA4311A has for the IO that connect through a harness. The Schottky diodes from the SN74CBT devices will help with any inductive ringing due to harnesses. It clamps the voltage to lower than what the internal diodes could conduct. It prevents that energy from going into unintended places within the device, that inductive energy is routed to the schottkys which were designed to handed the current.
    -Francis Houde
  • Hello Francis,

    Could I know SN74CBTLV3384 also have schottky diode to prevent inductive ringing to clamp voltage? Thank you.

    BR
    Patrick
  • Hello Patrick,
    I split the thread and moved it to our switches group which supports this product.
    -Francis Houde