SBOS945B November   2020  – April 2021 INA849

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Adjustable Gain Setting
      2. 8.3.2 Gain Drift
      3. 8.3.3 Wide Input Common-Mode Range
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Reference Pin
      2. 9.1.2 Input Bias Current Return Path
      3. 9.1.3 Thermal Effects due to Power Dissipation
    2. 9.2 Typical Application
      1. 9.2.1 Sensor Conditioning Circuit
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
      2. 9.2.2 Phantom Power in Microphone Preamplifier Circuit
  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 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

9.1.2 Input Bias Current Return Path

The input impedance of the INA849 is extremely high (approximately 100 GΩ). However, a path must be provided for the input bias current of both inputs. This input bias current is typically 6 nA. High input impedance means that this input bias current changes little with varying input voltage.

Input circuitry must provide a path for this input bias current for proper operation. Figure 9-4 shows various provisions for an input bias current path. Without a bias current path, the inputs float to a potential that exceeds the common-mode range of the INA849, and the input amplifiers saturate. If the differential source resistance is low, the bias current return path connects to one input (as shown in the thermocouple example). With a higher source impedance, using two equal resistors provides a balanced input with possible advantages of a lower input offset voltage as a result of bias current, and better high-frequency common-mode rejection.

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NOTE: Center tap in the transformer provides bias current return.
Figure 9-4 Providing an Input Common-Mode Current Path