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SN55LVCP22-SP: EN & SEL unused inputs

Steve Widener
Genius 9575 points
Part Number: SN55LVCP22-SP
Other Parts Discussed in Thread: SN55LVCP22EVM-CVAL,

1)      For an application in which SN55LVCP22-SP‘s EN0/1 and/or SEL0/1 is not needed to be toggled, would you recommend a certain resistor value for pulling the input low/high? Would you recommend hard-tying these inputs to an input voltage such as the implementation for SN55LVCP22EVM-CVAL?

2)      Due to limited board real-estate, would it be a safe assumption that these could be consolidated? Do you have any specific requirements for this IC such as an impedance profile that needs to be met?

  • 0
    TI__Genius 9575 points
    Follow-up:

    Do you have a recommendation for terminating an unused input for the SN55LVCP22-SP if it were to always be used as a splitter or in a single repeater function?
  • 0 in reply to Steve Widener
    TI__Guru 62930 points
    Steve, these are digital inputs. So, they can be biased to the logic level desired. This can be through pullup, pull down, or direct connection to valid logic high or low.
    These digital inputs have internal weak pull downs (to GND). Some space customers do not rely internal pullups or downs to provide proper logic levels and will always bias static controls through resistor to proper level. Likely this is to create fault isolation.
    On the EVM, GND will normally be offset to VCC-2, so control signals must be biased to VCC01 on board for logic low. Ie, the pull down will not bias to proper level. In a typical system, GND will bias to proper logic level with the internal pulldown.
    Hopefully this did not confuse matters.

    Personally, using a 10kohm to VCC or GND (in system) would be reasonable choice for biasing. There will be virtually no current flow due to high impedance input anyways.

    Regards,
    Wade