SBOS969E October   2019  – May 2021 OPA2991 , OPA4991 , OPA991

PRODMIX  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information for Single Channel
    5. 6.5 Thermal Information for Dual Channel
    6. 6.6 Thermal Information for Quad Channel
    7. 6.7 Electrical Characteristics
    8. 6.8 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Input Protection Circuitry
      2. 7.3.2  EMI Rejection
      3. 7.3.3  Thermal Protection
      4.     
      5. 7.3.4  Capacitive Load and Stability
      6. 7.3.5  Common-Mode Voltage Range
      7. 7.3.6  Phase Reversal Protection
      8. 7.3.7  Electrical Overstress
      9. 7.3.8  Overload Recovery
      10. 7.3.9  Typical Specifications and Distributions
      11. 7.3.10 Packages With an Exposed Thermal Pad
      12. 7.3.11 Shutdown
    4. 7.4 Device Functional Modes
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Low-Side Current Measurement
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curves
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
        1. 11.1.1.1 TINA-TI (Free Software Download)
        2. 11.1.1.2 TI Precision Designs
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Related Links
    4. 11.4 Receiving Notification of Documentation Updates
    5. 11.5 Support Resources
    6. 11.6 Trademarks
    7. 11.7 Electrostatic Discharge Caution
    8. 11.8 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

Detailed Design Procedure

The transfer function of the circuit in Figure 8-1 is given in Equation 1:

Equation 1. GUID-55791B5C-190A-4DF4-B254-3CC786FBF411-low.gif

The load current (ILOAD) produces a voltage drop across the shunt resistor (RSHUNT). The load current is set from 0 A to 1 A. To keep the shunt voltage below 100 mV at maximum load current, the largest shunt resistor is defined using Equation 2:

Equation 2. GUID-C45013C6-1441-4BF9-AF6C-656A61F6F3B0-low.gif

Using Equation 2, RSHUNT is calculated to be 100 mΩ. The voltage drop produced by ILOAD and RSHUNT is amplified by the OPA991 to produce an output voltage of 0 V to 4.9 V. The gain needed by the OPA991 to produce the necessary output voltage is calculated using Equation 3:

Equation 3. GUID-DEB413BB-9F8B-46D5-947C-A6001295FF71-low.gif

Using Equation 3, the required gain is calculated to be 49 V/V, which is set with resistors RF and RG. Equation 4 is used to size the resistors, RF and RG, to set the gain of the OPA991 to 49 V/V.

Equation 4. GUID-D7251FDF-DA40-4323-8F1C-8EDCDE56A220-low.gif

Choosing RF as 360 kΩ, RG is calculated to be 7.5 kΩ. RF and RG were chosen as 360 kΩ and 7.5 kΩ because they are standard value resistors that create a 49:1 ratio. Other resistors that create a 49:1 ratio can also be used. Figure 8-2 shows the measured transfer function of the circuit shown in Figure 8-1.