SBOSAI0B December   2023  – September 2024 OPA310-Q1

PRODMIX  

  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 Operating Voltage
      2. 6.3.2 Rail-to-Rail Input
      3. 6.3.3 Rail-to-Rail Output
      4. 6.3.4 Capacitive Load and Stability
      5. 6.3.5 Overload Recovery
      6. 6.3.6 EMI Rejection
      7. 6.3.7 ESD and Electrical Overstress
      8. 6.3.8 Input ESD Protection
      9. 6.3.9 Shutdown Function
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 OPAx310-Q1 Low-Side, Current Sensing Application
        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 Documentation Support
      1. 8.1.1 Related Documentation
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4.     Trademarks
    5. 8.4 Electrostatic Discharge Caution
    6. 8.5 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and 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. VOUT=  ILOAD ×RSHUNT× Gain

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

Equation 2. RSHUNT= VSHUNT_MAXILOAD_MAX= 100 mV1 A=100 mΩ

Using Equation 2, RSHUNT is calculated to be 100mΩ. The voltage drop produced by ILOAD and RSHUNT is amplified by the OPAx310-Q1 to produce an output voltage of approximately 0V to 4.9V. The gain needed by the OPAx310-Q1 to produce the necessary output voltage is calculated using Equation 3.

Equation 3. Gain=VOUT_MAX   -  VOUT_MINVIN_MAX   -  VIN_MIN

Using Equation 3, the required gain is calculated to be 49V/V, which is set with resistors RF and RG. Equation 4 sizes the resistors RF and RG, to set the gain of the OPAx310-Q1 to 49V/V.

Equation 4. Gain=1+ RFRG

Selecting RF as 57.6 kΩ and RG as 1.2 kΩ provides a combination that equals 49V/V. Figure 7-2 shows the measured transfer function of the circuit shown in Figure 7-1. Notice that the gain is only a function of the feedback and gain resistors. This gain is adjusted by varying the ratio of the resistors and the actual resistors values are determined by the impedance levels that the designer wants to establish. The impedance level determines the current drain, the effect that stray capacitance has, and a few other behaviors. There is no optimal impedance selection that works for every system; choose an impedance that is best for the system parameters.