SNOS630E August   2000  – February 2024 LMC6081 , LMC6082 , LMC6084

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 LMC6081
    5. 5.5 Thermal Information LMC6082
    6. 5.6 Thermal Information LMC6084
    7. 5.7 Electrical Characteristics
    8. 5.8 Typical Characteristics
  7. 6Application and Implementation
    1. 6.1 Application Information
      1. 6.1.1 Amplifier Topology
      2. 6.1.2 Compensating for Input Capacitance
      3. 6.1.3 Capacitive Load Tolerance
      4. 6.1.4 Latch-Up
    2. 6.2 Typical Applications
      1. 6.2.1 Typical Single-Supply Applications
      2. 6.2.2 Instrumentation Amplifier
    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 Receiving Notification of Documentation Updates
    2. 7.2 Support Resources
    3. 7.3 Trademarks
    4. 7.4 Electrostatic Discharge Caution
    5. 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)
  • Y|0
Thermal pad, mechanical data (Package|Pins)
Orderable Information

6.1.2 Compensating for Input Capacitance

The use of large value feedback resistors is quite common for amplifiers with ultra-low input current, like the LMC608x.

Although the LMC608x are highly stable over a wide range of operating conditions, certain precautions must be met to achieve the desired pulse response when a large feedback resistor is used. Large feedback resistors and even small values of input capacitance, due to transducers, photodiodes, and circuit board parasitics, reduce phase margins.

When a high input impedance is demanded, guarding of the LMC608x is suggested. Guarding input lines not only reduces leakage, but lowers stray input capacitance as well. (See Printed-Circuit-Board Layout for High Impedance Work)

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

Equation 1. 12πR1CIN ≥ 12πR2Cf

or

Equation 2. R1CIN ≤R2Cf

The exact value of CIN can be difficult to find, so Cf can be experimentally adjusted so that the desired pulse response is achieved. Refer to the LMC66x for a more detailed discussion on compensating for input capacitance.

GUID-BBEBCAC2-AA8D-4056-BF6C-1D6869D966CE-low.pngFigure 6-1 Canceling the Effect of Input Capacitance