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LTC2865 powered but pins floating

I'm trying to use the HTG-FMC-RS485 board which has multiple LTC2865's on a single card connected to an FMC connector to allow an FPGA interface. The problem is, not all FMC pins on my FPGA board are routed, meaning I have several LTC2865's that are powered, but have all TTL pins floating with no pull-ups or pull-downs.

Obviously I can't use the floating parts, but I'm wondering if this will cause some bad side effects?. Are there internal pull-ups/pull-downs that will keep the device in a quiet state, or will the floating pins cause excessive switching, power draw, or noise? The RS-485 differential lines themselves do have a pull up/down and termination resistors, just nothing on the RO,DI,RE,DE, or SLO pins.

  • Hi rdb9879, 

    Yes if the pin is an input pin and is left open then it will be floating and it will susceptible to noise.  it is therefore advisable not the leave the pin open. it must be pulled high to Vdd through a resistor or pulled to ground. I don't think there's a pullup/pulldown on them.