SBOS301C May   2004  – December 2025 LOG114

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration
  6. 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 (±5V)
    6. 5.6 Electrical Characteristics (5V)
    7. 5.7 Typical Characteristics: VS = ±5V
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Logarithmic and Difference Amplifier
      2. 6.3.2 COM Voltage Range
      3. 6.3.3 VCM IN
      4. 6.3.4 Auxiliary Operational Amplifier
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Applications Information
      1. 7.1.1 Transfer Function
      2. 7.1.2 Input Current Range
      3. 7.1.3 Setting the Reference Current
      4. 7.1.4 Negative Input Currents
      5. 7.1.5 Voltage Inputs
      6. 7.1.6 High-Current Linearity Correction
      7. 7.1.7 Error Sources
        1. 7.1.7.1 Accuracy
        2. 7.1.7.2 Total Error
        3. 7.1.7.3 Errors RTO and RTI
        4. 7.1.7.4 Log Conformity
        5. 7.1.7.5 Individual Error Components
    2. 7.2 Typical Applications
      1. 7.2.1 Design Example for Dual-Supply Configuration
      2. 7.2.2 Design Example for Single-Supply Configuration
      3. 7.2.3 Advantages of Dual−Supply Operation
      4. 7.2.4 Log Ratio
      5. 7.2.5 Data Compression
      6. 7.2.6 3.3V Operation
      7. 7.2.7 Erbium-Doped Fiber Optic Amplifier (EDFA)
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Device Nomenclature
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
      2. 8.2.2 PSpice® for TI
      3. 8.2.3 TINA-TI™ (Free Software Download)
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

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

6.3.4 Auxiliary Operational Amplifier

The LOG114 features two additional wide bandwidth amplifiers, A4 and A5. These amplifiers are for use to support functions such as single-ended to differential conversion, or single-ended gain, scaling, offsetting, threshold detection, filtering, or other functions.

To verify operational amplifier stability, an isolation resistor, or Riso is sometimes needed especially when the operational amplifier is driving capacitive loads. Figure 6-1 is an example of what the isolation resistor architecture looks like.

LOG114 Example of Isolation ResistorFigure 6-1 Example of Isolation Resistor

As shown in Figure 5-21, for capacitive loads above 50pF, include an Riso in the circuit to maintain at least 45° of phase margin.

Another cause of operational amplifier instability can come from having large impedance feedback resistors. This instability results in the feedback resistor interacting with the internal input capacitors of the auxiliary amplifiers. There are two options to correcting this instability. The first one is lowering the resistor values in the feedback loop.

The second option, as shown in Figure 6-2, is to put a feedback capacitor in the feedback loop in parallel with the feedback resistor.

LOG114 Example of Feedback CapacitorFigure 6-2 Example of Feedback Capacitor