SCAS982 March   2024 SN74AHCT257

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6.   6
  7.   7
  8. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Switching Characteristics
    7. 5.7 Noise Characteristics
    8. 5.8 Typical Characteristics
  9. 6 Parameter Measurement Information
  10. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Balanced CMOS 3-State Outputs
      2. 7.3.2 TTL-Compatible CMOS Inputs
      3. 7.3.3 Clamp Diode Structure
    4. 7.4 Device Functional Modes
  11. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
    3. 8.3 Design Requirements
      1. 8.3.1 Power Considerations
      2. 8.3.2 Input Considerations
      3. 8.3.3 Output Considerations
    4. 8.4 Detailed Design Procedure
    5. 8.5 Application Curve
    6. 8.6 Power Supply Recommendations
    7. 8.7 Layout
      1. 8.7.1 Layout Guidelines
      2. 8.7.2 Layout Example
  12. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  13. 10Revision History
  14. 11Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • BQB|16
  • PW|16
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.4 Detailed Design Procedure

  1. Add a decoupling capacitor from VCC to GND. The capacitor needs to be placed physically close to the device and electrically close to both the VCC and GND pins. An example layout is shown in the Layout section.
  2. Ensure the capacitive load at the output is ≤ 50pF. This is not a hard limit; by design, however, it will optimize performance. This can be accomplished by providing short, appropriately sized traces from the SN74AHCT257 to one or more of the receiving devices.
  3. Ensure the resistive load at the output is larger than (VCC / IO(max))Ω. Doing this will prevent the maximum output current from the Absolute Maximum Ratings from being violated. Most CMOS inputs have a resistive load measured in MΩ; much larger than the minimum calculated previously.
  4. Thermal issues are rarely a concern for logic gates; the power consumption and thermal increase, however, can be calculated using the steps provided in the application report, CMOS Power Consumption and Cpd Calculation.