SBOS923I December   2017  – July 2024 LMV321A , LMV324A , LMV358A

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Functions and Configurations
  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: LMV321A
    5. 5.5 Thermal Information: LMV358A
    6. 5.6 Thermal Information: LMV324A
    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 Input Common Mode Range
      3. 6.3.3 Rail-to-Rail Output
      4. 6.3.4 Overload Recovery
    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 LMV3xxA 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
      2. 7.2.2 Single-Supply Photodiode Amplifier
        1. 7.2.2.1 Design Requirements
        2. 7.2.2.2 Detailed Design Procedure
        3. 7.2.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
      1. 7.3.1 Input and ESD Protection
    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. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

7.2.2.2 Detailed Design Procedure

The transfer function between the output voltage (VOUT), the input current, (IIN) and the reference voltage (VREF) is defined in Equation 5.

Equation 5. V O U T   = I I N   ×   R F   +   V R E F  

Where:

Equation 6. V R E F   = V +   ×   R 1   ×   R 2 R 1   +   R 2

Set VREF to 100 mV to meet the minimum output voltage level by setting R1 and R2 to meet the required ratio calculated in Equation 7.

Equation 7. V R E F V +   =   0.1   V 3.3   V   =   0.0303

The closest resistor ratio to meet this ratio sets R1 to 11.5 kΩ and R2 to 357 Ω.

The required feedback resistance can be calculated based on the input current and desired output voltage.

Equation 8. R F   =   V O U T   -   V R E F I I N   =   3.2   V   -   0.1   V 10   µ A   = 310     k V A   ≈   309   k Ω

Calculate the value for the feedback capacitor based on RF and the desired –3-dB bandwidth, (f–3dB) using Equation 9.

Equation 9. C F   =   1 2 × π × R F × f - 3   d B   =   1 2 × π × 309   k Ω × 50   k H z   = 10.3   p F   ≈   10   p F

The minimum op amp bandwidth required for this application is based on the value of RF, CF, and the capacitance on the INx– pin of the LMV358A which is equal to the sum of the photodiode shunt capacitance, (CPD) the common-mode input capacitance, (CCM) and the differential input capacitance (CD) as Equation 10 shows.

Equation 10. C I N   =   C P D   +   C C M   +   C D   =   47   p F   +   5   p F   + 1   p F   =   53   p F

The minimum op amp bandwidth is calculated in Equation 11.

Equation 11. f = B G W   ≥   C I N   +   C F 2   ×   π   ×   R F   ×   C F 2   ≥   324   k H z

The 1-MHz bandwidth of the LMV3xxA meets the minimum bandwidth requirement and remains stable in this application configuration.