SCASE14 September   2024 SN74AC3G98

ADVANCE INFORMATION  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Electrical Characteristics
    4. 5.4 Recommended Operating Conditions
    5. 5.5 Thermal Information
    6. 5.6 Switching Characteristics
  7. 6 Parameter Measurement Information
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Balanced CMOS Push-Pull Outputs
      2. 7.3.2 CMOS Schmitt-Trigger Inputs
      3. 7.3.3 Clamp Diode Structure
    4. 7.4 Device Functional Modes
    5. 7.5 Combinatorial Logic Configurations
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
        1. 8.2.1.1 Power Considerations
        2. 8.2.1.2 Input Considerations
        3. 8.2.1.3 Output Considerations
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curves
      4. 8.2.4 Power Supply Recommendations
      5. 8.2.5 Layout
        1. 8.2.5.1 Layout Guidelines
        2. 8.2.5.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Receiving Notification of Documentation Updates
    2. 9.2 Support Resources
    3. 9.3 Trademarks
    4. 9.4 Electrostatic Discharge Caution
    5. 9.5 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information
    1. 11.1 Tape and Reel Information
    2. 11.2 Mechanical Data

8.2.1.2 Input Considerations

Input signals must cross Vt-(min) to be considered a logic LOW, and Vt+(max) to be considered a logic HIGH. Do not exceed the maximum input voltage range found in the Absolute Maximum Ratings.

Unused inputs must be terminated to either VCC or ground. The unused inputs can be directly terminated if the input is completely unused, or they can be connected with a pull-up or pull-down resistor if the input will be used sometimes, but not always. A pull-up resistor is used for a default state of HIGH, and a pull-down resistor is used for a default state of LOW. The drive current of the controller, leakage current into the SN74AC3G98 (as specified in the Electrical Characteristics), and the desired input transition rate limits the resistor size. A 10kΩ resistor value is often used due to these factors.

The SN74AC3G98 has no input signal transition rate requirements because it has Schmitt-Trigger inputs.

Another benefit to having Schmitt-Trigger inputs is the ability to reject noise. Noise with a large enough amplitude can still cause issues. To know how much noise is too much, please refer to the ΔVT(min) in the Electrical Characteristics. This hysteresis value will provide the peak-to-peak limit.

Unlike what happens with standard CMOS inputs, Schmitt-Trigger inputs can be held at any valid value without causing huge increases in power consumption. The typical additional current caused by holding an input at a value other than VCC or ground is plotted in the Typical Characteristics.

Refer to the Feature Description section for additional information regarding the inputs for this device.