SNVSCM5 January   2024 LMR43606-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 System Characteristics
    7. 6.7 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Enable, Start-Up, and Shutdown
      2. 7.3.2  External CLK SYNC (With MODE/SYNC)
        1. 7.3.2.1 Pulse-Dependent MODE/SYNC Pin Control
      3. 7.3.3  Adjustable Switching Frequency (with RT)
      4. 7.3.4  Power-Good Output Operation
      5. 7.3.5  Internal LDO, VCC, and VOUT/FB Input
      6. 7.3.6  Bootstrap Voltage and VBOOT-UVLO (BOOT Terminal)
      7. 7.3.7  Output Voltage Selection
      8. 7.3.8  Spread Spectrum
      9. 7.3.9  Soft Start and Recovery from Dropout
        1. 7.3.9.1 Recovery from Dropout
      10. 7.3.10 Current Limit and Short Circuit
      11. 7.3.11 Thermal Shutdown
      12. 7.3.12 Input Supply Current
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Standby Mode
      3. 7.4.3 Active Mode
        1. 7.4.3.1 CCM Mode
        2. 7.4.3.2 Auto Mode – Light-Load Operation
          1. 7.4.3.2.1 Diode Emulation
          2. 7.4.3.2.2 Frequency Reduction
        3. 7.4.3.3 FPWM Mode – Light-Load Operation
        4. 7.4.3.4 Minimum On-Time (High Input Voltage) Operation
        5. 7.4.3.5 Dropout
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  Choosing the Switching Frequency
        2. 8.2.2.2  Setting the Output Voltage
          1. 8.2.2.2.1 FB for Adjustable Output
        3. 8.2.2.3  Inductor Selection
        4. 8.2.2.4  Output Capacitor Selection
        5. 8.2.2.5  Input Capacitor Selection
        6. 8.2.2.6  CBOOT
        7. 8.2.2.7  VCC
        8. 8.2.2.8  CFF Selection
        9. 8.2.2.9  External UVLO
        10. 8.2.2.10 Maximum Ambient Temperature
      3. 8.2.3 Application Curves
    3. 8.3 Best Design Practices
    4. 8.4 Power Supply Recommendations
    5. 8.5 Layout
      1. 8.5.1 Layout Guidelines
        1. 8.5.1.1 Ground and Thermal Considerations
      2. 8.5.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Third-Party Products Disclaimer
      2. 9.1.2 Device Nomenclature
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

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

8.2.2.10 Maximum Ambient Temperature

As with any power conversion device, the LMR43606-Q1 dissipates internal power while operating. The effect of this power dissipation is to raise the internal temperature of the converter above ambient. The internal die temperature (TJ) is a function of the ambient temperature, the power loss, and the effective thermal resistance, RθJA, of the device, and PCB combination. The maximum junction temperature for the LMR43606-Q1 must be limited to 150°C. This limit establishes a limit on the maximum device power dissipation and, therefore, the load current. Equation 13 shows the relationships between the important parameters. Seeing that larger ambient temperatures (TA) and larger values of RθJA reduce the maximum available output current is easy. The converter efficiency can be estimated by using the curves provided in this data sheet. If the desired operating conditions cannot be found in one of the curves, interpolation can be used to estimate the efficiency. Alternatively, the EVM can be adjusted to match the desired application requirements and the efficiency can be measured directly. The correct value of RθJA is more difficult to estimate. For more information reference Semiconductor and IC Package Thermal Metrics application report.

Equation 13. IOUT|MAX=TJ-TARθJA×η1-η×1VOUT

where

  • η is the efficiency.

The effective RθJA is a critical parameter and depends on many factors such as the following:

  • Power dissipation
  • Air temperature and flow
  • PCB area
  • Copper heat-sink area
  • Number of thermal vias under the package
  • Adjacent component placement

Use Equation 14 to estimate the IC junction temperature for a given operating condition.

Equation 14. TJ≅TA+RθJA×IC Power Loss

where

  • TJ is the IC junction temperature (ºC).
  • TA is the ambient temperature (ºC).
  • RθJA is the thermal resistance (ºC/W).
  • IC power loss is the power loss for the IC (W).

The IC Power loss mentioned above is the overall power loss minus the loss that comes from the inductor DC resistance. The overall power loss can be approximated by using WEBENCH for a specific operating condition and temperature.

Use the following resources as guides to optimal thermal PCB design and estimating RθJA for a given application environment: