SBOS792A August   2017  – January 2018 INA828

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      INA828 Simplified Internal Schematic
      2.      Typical Distribution of Input Offset Voltage Drift
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin 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 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Setting the Gain
        1. 7.3.1.1 Gain Drift
      2. 7.3.2 EMI Rejection
        1. Table 2. INA828 EMIRR for Frequencies of Interest
      3. 7.3.3 Input Common-Mode Range
      4. 7.3.4 Input Protection
      5. 7.3.5 Operating Voltage
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Reference Terminal
    2. 8.2 Input Bias Current Return Path
    3. 8.3 PCB Assembly Effects on Precision
    4. 8.4 Typical Application
      1. 8.4.1 Design Requirements
      2. 8.4.2 Detailed Design Procedure
      3. 8.4.3 Application Curves
    5. 8.5 Other Application Examples
      1. 8.5.1 Resistance Temperature Detector Interface
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8.4.2 Detailed Design Procedure

There are two modes of operation for the circuit shown in Figure 68: current input and voltage input. This design requires R1 >> R2 >> R3. Given this relationship, Equation 3 calculates the current input mode transfer function.

Equation 3. INA828 q_curr_mode_xfer_function_bos562.gif

where

  • G represents the gain of the instrumentation amplifier
  • VD represents the differential voltage at the INA828 inputs
  • VREF is the voltage at the INA828 REF pin
  • IIN is the input current

Equation 4 shows the transfer function for the voltage input mode.

Equation 4. INA828 q_voltage_input_mode_xfer_function_bos562.gif

where

  • VIN is the input voltage

R1 sets the input impedance of the voltage input mode. The minimum typical input impedance is 100 kΩ. 100 kΩ is selected for R1 because increasing the R1 value also increases noise. The value of R3 must be extremely small compared to R1 and R2. 20 Ω for R3 is selected because that resistance value is much smaller than R1 and yields an input voltage of ±400 mV when operated in current mode (±20 mA).

Use Equation 5 to calculate R2 given VD = ±400 mV, VIN = ±10 V, and R1 = 100 kΩ.

Equation 5. INA828 q_r2_vd_vin_r1_bos562.gif

The value obtained from Equation 5 is not a standard 0.1% value, so 4.17 kΩ is selected. R1 and R2 also use 0.1% tolerance resistors to minimize error.

Use Equation 6 to calculate the ideal gain of the instrumentation amplifier.

Equation 6. INA828 q_ideal_gain_bos562.gif

Equation 7 calculates the gain-setting resistor value using the INA828 gain equation, Equation 1.

Equation 7. INA828 ai_EQ002_SBOS792.gif

10.5 kΩ is a standard 0.1% resistor value that can be used in this design.