SBOSAI9B December   2023  – March 2024 INA500

PRODMIX  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and Functions
  7. 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 - INA500A
    6. 6.6 Electrical Characteristics - INA500B
    7. 6.7 Electrical Characteristics - INA500C
    8. 6.8 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Gain Options and Resistors
        1. 7.3.1.1 Gain Error and Drift
      2. 7.3.2 Input Common-Mode Voltage Range
      3. 7.3.3 EMI Rejection
      4. 7.3.4 Typical Specifications and Distributions
      5. 7.3.5 Electrical Overstress
    4. 7.4 Device Functional Modes
  9. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Reference Pin
    2. 8.2 Typical Applications
      1. 8.2.1 Battery Monitoring using Difference Amplifier
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Development Support
        1. 9.1.1.1 PSpice® for TI
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • DBV|6
  • DCK|6
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.2.1.2 Detailed Design Procedure

This section provides basic calculations for the INA500C difference amplifier with respect to the given design requirements.

Firstly, the 12V battery voltage needs to be attenuated and interfaced to ADC reference voltage of 3V. This requires a G = ¼ or 0.25V/V and hence INA500C is chosen for the application.

Equation 1. G a i n =   V B A T V A D C =   12 3 =   1 4 = 0.25    

The maximum common-mode range of INA500 in a gain of 0.25 is given by,

Equation 2. V C M _ M A X = 5 * V + –   4 * V R E F = 5 * 3 – 4 * 0 = 15 V

This is well within the requirements for sensing 12V battery voltage and the common-mode rejection ratio (CMRR) referred to output is a minimum of 62dB as per Electrical Characteristics table. This corresponds to a attenuation factor of 1 1250 . This helps attenuate the 100mV common-mode error shown in the Figure 8-2 to just 80μV.

Equation 3. C M E r r _ R T O = 100 m V 1250   = 80 μ V , when referred to INA500C's output.

Next, INA500C has input impedance of 1.68MΩ as per the Electrical Characteristics table. Assuming a full battery voltage of 12V, the input current through the resistor is calculated as,

Equation 4.   I R I N =   V B A T R I N =   12 1.68 M = 7.2 μ A    

This input current through the resistor adds to the amplifier quiescent current of 13.5μA resulting in a total current consumption of 20.7μA, which meets the design requirement of 30μA.

Equation 5. I t o t a l =   I R I N +   I Q

The next step is to calculate the other error sources in the application. Maximum gain error and offset error as per Electrical Characteristics table are 0.05% and 2.5mV for the Gain = 0.25V/V.

Equation 6. T o t a l   E r r o r =   ( 0.0005 * 12 ) 2 +   0.0025 2 = 6.5 m V

For an 8 bit, 3V ADC, VLSB is calculated as,

Equation 7. V L S B =   3 2 8 = 11.7 m V

The total error of 6.5mV that was calculated is approximately 0.5LSB of ADC full scale voltage of 3V and hence meets the 8-bit accuracy requirement.

Note, that the errors across temperature are not calculated here but can be easily included in the error analysis based on the drift specifications provided in the Electrical Characteristics table as per the application's temperature requirements. These drift errors and noise often do not heavily affect the performance at 8 bit accuracy levels. Finally, calibration of offset and gain error can improve the accuracy beyond 10 to 12 bits as these factors can be the major sources of error in the application.