SNOS724F August   2000  – February 2024 LMC6492 , LMC6494

PRODUCTION DATA  

  1.   1
  2. 1Features
  3. 2Applications
  4. 3Description
  5. 4Pin Configuration and Functions
  6. 5Specifications
    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 Typical Characteristics
  7. 6Application and Implementation
    1. 6.1 Application Information
      1. 6.1.1 Input Common-Mode Voltage Range
      2. 6.1.2 Rail-to-Rail Output
      3. 6.1.3 Compensating for Input Capacitance
      4. 6.1.4 Capacitive Load Tolerance
    2. 6.2 Typical Application
      1. 6.2.1 Application Circuits
    3. 6.3 Layout
      1. 6.3.1 Layout Guidelines
        1. 6.3.1.1 Printed Circuit Board Layout For High-Impedance Work
  8. 7Device and Documentation Support
    1. 7.1 Device Support
      1. 7.1.1 Development Support
        1. 7.1.1.1 Spice Macromodel
        2. 7.1.1.2 PSpice® for TI
        3. 7.1.1.3 TINA-TI™ Simulation Software (Free Download)
        4. 7.1.1.4 DIP-Adapter-EVM
        5. 7.1.1.5 DIYAMP-EVM
        6. 7.1.1.6 TI Reference Designs
        7. 7.1.1.7 Filter Design Tool
    2. 7.2 Receiving Notification of Documentation Updates
    3. 7.3 Support Resources
    4.     Trademarks
    5. 7.4 Electrostatic Discharge Caution
    6. 7.5 Glossary
  9. 8Revision History
  10. 9Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • D|8
Thermal pad, mechanical data (Package|Pins)
Orderable Information

6.1.3 Compensating for Input Capacitance

Large values of feedback resistance are commonly used for amplifiers with ultra-low input current, such as the LMC649x.

Although the LMC649x is highly stable over a wide range of operating conditions, make sure that certain precautions are met to achieve the desired pulse response when a large feedback resistor is used. Large feedback resistors with even small values of input capacitance (due to transducers, photodiodes, and circuit board parasitics) reduce phase margins.

When high input impedances are demanded, guarding of the LMC649x is suggested. Guarding input lines not only reduces leakage, but also lowers stray input capacitance. See Printed-Circuit-Board Layout for High Impedance Work.

The effect of input capacitance can be compensated by adding a capacitor, Cf, around the feedback resistors (as in Figure 6-1 ) so that:

Equation 1. GUID-224A52E6-DD05-4140-BCAE-F673D75D5CB1-low.png

or

Equation 2. R1 CIN ≤ R2 Cf

The exact value of CIN is difficult to know; therefore, Cf can be experimentally adjusted so that the desired pulse response is achieved. See the LMC660 and LMC662 for a more detailed discussion on compensating for input capacitance.

GUID-2B5EA375-2D66-4040-A771-E8D1A1AA50E8-low.pngFigure 6-5 Canceling the Effect of Input Capacitance