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The correct way to use LTC4311

Hi, I would like a guidance on how the LTC4311 is supposed to be installed. My design will have a master device and max.10 slaves daisy-chained in interchangeable order, the cable length between devices is approximately 15cm. 

  • The datasheet is showing only 1 accelerator IC is needed for all the N devices (model A), is it correct?
  • In the case of model A, where is the IC is supposed to be placed? at the beginning (master device) or the last device? Although this may be an issue since the order is not fixed.
  • If each cable is increased to 50cm and the device number is increased to more than 10, does the model A design still valid? Will model B with accelerator IC on each slave device make any difference or just plain incorrect?
  • If model B is valid, does a pull-up resistor needed for each IC?

Thank you in advance.

  • Hi Adam,

    The LTC4311 is only active when it detects a rising edge on a bus line. It needs to see a voltage threshold crossed at a minimum slew rate to trigger the rise time acceleration. The LTC4311 is slew rate limited, so there can be multiple LTC4311 operating in parallel.

    The application bus described here is very long. There will be a lot of parasitic capacitance on the bus, so signal characteristics may be substantially different at different locations. The best signalling may be with parallel LTC4311 and pull-ups distributed in the system.

    The LTC4311 allows the 400pF capacitance limit to be greatly exceeded and/or use weak pull-ups for power savings. This application will have a good bit of parasitic capacitance from all this cabling and the LTC4311(s) will help drive that load. But sending single-ended signals off-board may leave the design vulnerable to cross talk between the lines and allow noise from other sources to disturb the I2C signalling. The LTC4331 or LT3960 would provide more robust signalling over cables because they use differential signaling.