SBOSA12H March   2020  – March 2024 OPA2991-Q1 , OPA4991-Q1 , OPA991-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  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 for Single Channel
    5. 5.5 Thermal Information for Dual Channel
    6. 5.6 Thermal Information for Quad Channel
    7. 5.7 Electrical Characteristics
    8. 5.8 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1  Input Protection Circuitry
      2. 6.3.2  EMI Rejection
      3. 6.3.3  Thermal Protection
      4. 6.3.4  Capacitive Load and Stability
      5. 6.3.5  Common-Mode Voltage Range
      6. 6.3.6  Phase Reversal Protection
      7. 6.3.7  Electrical Overstress
      8. 6.3.8  Overload Recovery
      9. 6.3.9  Typical Specifications and Distributions
      10. 6.3.10 Shutdown
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Applications
      1. 7.2.1 Low-Side Current Measurement
        1. 7.2.1.1 Design Requirements
        2. 7.2.1.2 Detailed Design Procedure
        3. 7.2.1.3 Application Curve
    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 Development Support
        1. 8.1.1.1 TINA-TI (Free Software Download)
        2. 8.1.1.2 TI Precision Designs
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    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

7.2.1.2 Detailed Design Procedure

The transfer function of the circuit in Figure 7-1 is given in Equation 1.

Equation 1. V O U T   = I L O A D ×   R S H U N T × G a i n

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. R S H U N T   = V S H U N T _ M A X   I L O A D _ M A X   =   100   m V 1   A   =   100   m Ω

Using Equation 2, RSHUNT is calculated to be 100 mΩ. The voltage drop produced by ILOAD and RSHUNT is amplified by the OPA991-Q1 to produce an output voltage of 0 V to 4.9 V. The gain needed by the OPA991-Q1 to produce the necessary output voltage is calculated using Equation 3.

Equation 3. G a i n   = ( V O U T _ M A X   -   V O U T _ M I N ) ( V I N _ M A X   -   V I N _ M I N )

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-Q1 to 49 V/V.

Equation 4. G a i n   =   1   +   ( R F ) ( R G )

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 7-2 shows the measured transfer function of the circuit shown in Figure 7-1.