SNVS817B June   2012  – June 2019 LMR12015 , LMR12020

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Application Circuit
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Descriptions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 Recommended Operating Ratings
    3. 6.3 Electrical Characteristics
    4. 6.4 Typical Performance Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Boost Function
      2. 7.3.2  Low Input Voltage Considerations
      3. 7.3.3  High Output Voltage Considerations
      4. 7.3.4  Frequency Synchronization
      5. 7.3.5  Current Limit
      6. 7.3.6  Frequency Foldback
      7. 7.3.7  Soft Start
      8. 7.3.8  Output Overvoltage Protection
      9. 7.3.9  Undervoltage Lockout
      10. 7.3.10 Thermal Shutdown
    4. 7.4 Device Operation Modes
      1. 7.4.1 Enable Pin / Shutdown Mode
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Detailed Design Procedure
        1. 8.2.1.1  Custom Design With WEBENCH® Tools
        2. 8.2.1.2  Inductor Selection
          1. 8.2.1.2.1 Inductor Calculation Example
          2. 8.2.1.2.2 Inductor Material Selection
        3. 8.2.1.3  Input Capacitor
        4. 8.2.1.4  Output Capacitor
        5. 8.2.1.5  Catch Diode
        6. 8.2.1.6  Boost Diode (Optional)
        7. 8.2.1.7  Boost Capacitor
        8. 8.2.1.8  Output Voltage
        9. 8.2.1.9  Feedforward Capacitor (Optional)
        10. 8.2.1.10 Calculating Efficiency and Junction Temperature
          1. 8.2.1.10.1 Schottky Diode Conduction Losses
          2. 8.2.1.10.2 Inductor Conduction Losses
          3. 8.2.1.10.3 MOSFET Conduction Losses
          4. 8.2.1.10.4 MOSFET Switching Losses
          5. 8.2.1.10.5 IC Quiescent Losses
          6. 8.2.1.10.6 MOSFET Driver Losses
          7. 8.2.1.10.7 Total Power Losses
          8. 8.2.1.10.8 Efficiency Calculation Example
          9. 8.2.1.10.9 Calculating the LMR2015/20 Junction Temperature
      2. 8.2.2 Application Curves
      3. 8.2.3 LMR12015/20 Circuit Examples
  9. 9 Layout
    1. 9.1 Layout Considerations
      1. 9.1.1 Compact Layout
      2. 9.1.2 Ground Plane and Shape Routing
      3. 9.1.3 FB Loop
      4. 9.1.4 PCB Summary
  10. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Third-Party Products Disclaimer
      2. 10.1.2 Development Support
        1. 10.1.2.1 Custom Design With WEBENCH® Tools
    2. 10.2 Related Links
    3. 10.3 Receiving Notification of Documentation Updates
    4. 10.4 Community Resources
    5. 10.5 Trademarks
    6. 10.6 Electrostatic Discharge Caution
    7. 10.7 Glossary
  11. 11Mechanical, Packaging, and Orderable Information

Package Options

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

8.2.1.2.1 Inductor Calculation Example

Operating conditions for the LMR12015/20 are:

Equation 14. VIN = 7 – 16 V
Equation 15. fSW = 2 MHz
Equation 16. VOUT = 3.3 V
Equation 17. VD1 = 0.5 V
Equation 18. IOUT = 2 A

First the maximum duty cycle is calculated.

Equation 19. DMAX = (VOUT + VD1) / (VIN + VD1 – VDS) = (3.3 V + 0.5 V) / (7 V + 0.5 V – 0.3 V) = 0.528

Using Figure 27 gives us a recommended ripple ratio = 0.4.

Now the minimum duty cycle is calculated.

Equation 20. DMIN= (VOUT + VD1) / (VIN + VD1 – VDS) = (3.3 V + 0.5 V) / (16 V + 0.5 V – 0.3 V) = 0.235

The inductance can now be calculated.

Equation 21. L= (1 – DMIN) x (VOUT + VD1) / (IOUT × r × ƒSW) = (1 – 0.235) × (3.3 V + 0.5 V) / (2 A × 0.4 × 2 MHz) = 1.817 µH

This is close to the standard inductance value of 1.8 µH. This leads to a 1% deviation from the recommended ripple ratio, which is now 0.4038.

Finally, we check that the peak current does not reach the minimum current limit of 2.5 A.

Equation 22. ILPK = IOUT × (1 + r / 2) = 2 A × (1 + 0.4038 / 2 ) = 2.404 A

The peak current is less than 2.5 A, so the DC load specification can be met with this ripple ratio. To design for the LMR12015 simply replace IOUT = 1.5 A in the equations for ILPK and see that ILPK does not exceed the LMR12015 current limit of 2 A (min).