SCES581D JULY   2004  – October 2015 SN74LVC1GX04

UNLESS OTHERWISE NOTED, this document contains PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1  Absolute Maximum Ratings
    2. 6.2  ESD Ratings
    3. 6.3  Recommended Operating Conditions
    4. 6.4  Thermal Information
    5. 6.5  Electrical Characteristics
    6. 6.6  Switching Characteristics, SN74LVC1GX04
    7. 6.7  Switching Characteristics, SN74LVC1GX04
    8. 6.8  Switching Characteristics, SN74LVC1GX04
    9. 6.9  Operating Characteristics
    10. 6.10 Typical Characteristics
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curve
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Community Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • DBV|6
  • DRL|6
  • DCK|6
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

9.1 Application Information

The SN74LVC1GX04 contains a buffered and unbuffered inverter for the specific purpose of creating a crystal oscillator and driver with limited external components.

9.2 Typical Application

Figure 5 shows a typical application of the SN74LVC1GX04 in a Pierce oscillator circuit. The buffered inverter (SN74LVC1G04 portion) produces a rail-to-rail voltage waveform. The recommended load for the crystal shown in this example is 16 pF. The value of the recommended load (CL) can be found in the crystal manufacturer's data sheet.

Values of C1 and C2 are chosen to calculate CL in Equation 1 where C1  ≡ C2.

Equation 1. SN74LVC1GX04 eqapp1_ces581.gif

Rs is the current-limiting resistor, and the value depends on the maximum power dissipation of the crystal. Generally, the recommended value of Rs is specified in the crystal manufacturer's data sheet and, usually, this value is approximately equal to the reactance of C2 at resonance frequency, that is seen in Equation 2.

Equation 2. SN74LVC1GX04 eqapp2_ces581.gif

RF is the feedback resistor that is used to bias the inverter in the linear region of operation. Usually, the value is chosen to be within 1 MΩ to 10 MΩ.

SN74LVC1GX04 app3_ces581.gif Figure 5. Oscillator Circuit
SN74LVC1GX04 app4_ces581.gif Figure 6. Oscillator Circuit (Continued)

9.2.1 Design Requirements

The open-loop gain of the unbuffered inverter decreases as power-supply voltage decreases. This decreases the closed-loop gain of the oscillator circuit. The value of Rs can be decreased to increase the closed-loop gain, while maintaining the power dissipation of the crystal within the maximum limit.

Rs and C2 form a low-pass filter and reduce spurious oscillations. Component values can be adjusted, based on the desired cutoff frequency.

C2 can be increased over C1 to increase the phase shift and help in start-up of the oscillator. Increasing C2 may affect the duty cycle of the output voltage.

At high frequency, phase shift due to Rs becomes significant. In this case, Rs can be replaced by a capacitor to reduce the phase shift.

9.2.2 Detailed Design Procedure

After the selection of proper component values, the oscillator circuit should be tested using these components. To ensure that the oscillator circuit performs within the Recommended Operating Conditions, follow these steps:

  1. Without a crystal, the oscillator circuit should not oscillate. To check this, the crystal can be replaced by its equivalent parallel-resonant resistance.
  2. When the power-supply voltage drops, the closed-loop gain of the oscillator circuit reduces. Ensure that the circuit oscillates at the appropriate frequency at the lowest VCC and highest VCC.
  3. Ensure that the duty cycle, start-up time, and frequency drift over time is within the system requirements.

9.2.3 Application Curve

SN74LVC1GX04 app_curve_SCES581.gif Figure 7. VO vs VI Characteristics of Oscillator Amplifier