8.4 Standard CMOS Inputs

This device includes standard CMOS inputs. Standard CMOS inputs are high impedance and are typically modeled as a resistor in parallel with the input capacitance given in the Electrical Characteristics. The worst case resistance is calculated with the maximum input voltage, given in the Absolute Maximum Ratings, and the maximum input leakage current, given in the Electrical Characteristics, using Ohm's law (R = V ÷ I).

Standard CMOS inputs require that input signals transition between valid logic states quickly, as defined by the input transition time or rate in the Recommended Operating Conditions table. Failing to meet this specification will result in excessive power consumption and could cause oscillations. More details can be found in Implications of Slow or Floating CMOS Inputs.

Do not leave standard CMOS inputs floating at any time during operation. Unused inputs must be terminated at V_CC or GND. If a system will not be actively driving an input at all times, a pull-up or pull-down resistor can be added to provide a valid input voltage during these times. The resistor value will depend on multiple factors, however a 10-kΩ resistor is recommended and will typically meet all requirements.