SNVSBI9 October   2019 LMR33610


  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      Simplified Schematic
      2.      Efficiency vs Output Current VOUT = 5 V, 400 kHz
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and Functions
    1.     Pin Functions
  7. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Timing Characteristics
    7. 7.7 System Characteristics
    8. 7.8 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Power-Good Flag Output
      2. 8.3.2 Enable and Start-up
      3. 8.3.3 Current Limit and Short Circuit
      4. 8.3.4 Undervoltage Lockout and Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Auto Mode
      2. 8.4.2 Dropout
      3. 8.4.3 Minimum Switch On-Time
  9. Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1.  Custom Design With WEBENCH® Tools
        2.  Choosing the Switching Frequency
        3.  Setting the Output Voltage
        4.  Inductor Selection
        5.  Output Capacitor Selection
        6.  Input Capacitor Selection
        7.  CBOOT
        8.  VCC
        9.  CFF Selection
        10. External UVLO
        11. Maximum Ambient Temperature
      3. 9.2.3 Application Curves
    3. 9.3 What to Do and What Not to Do
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Ground and Thermal Considerations
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Development Support
        1. Custom Design With WEBENCH® Tools
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Support Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

Maximum Ambient Temperature

As with any power conversion device, the LMR33610 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 internal die temperature for the LMR33610 must be limited to 125°C. This establishes a limit on the maximum device power dissipation and, therefore, the load current. Equation 11 shows the relationships between the important parameters. It is easy to see that larger ambient temperatures (TA) and larger values of RθJA reduce the maximum available output current. 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, then 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. As stated in the Semiconductor and IC Package Thermal Metrics Application Report, the value of RθJA given in the table is not valid for design purposes and must not be used to estimate the thermal performance of the application. The values reported in that table were measured under a specific set of conditions that are rarely obtained in an actual application.

Equation 11. LMR33610 TJmax_eq2.gif


  • η = efficiency

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

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

The HSOIC (DDA) package uses a die attach paddle or thermal pad (PAD) to provide a place to solder down to the PCB heat-sinking copper. This provides a good heat conduction path from the regulator junction to the heat sink and must be properly soldered to the PCB heat sink copper. Typical examples of RθJA versus copper board area can be found in Figure 19. The copper area given in the graph is for each layer; the top and bottom layers are 2 ounce copper each, while the inner layers are 1 ounce.

Figure 20 and Figure 21 shows the typical curves of maximum output current versus ambient temperature. This data was taken with a device and PCB combination, giving an RθJA as noted in the graph. It must be remembered that the data given in these graphs are for illustration purposes only and the actual performance in any given application depends on all of the previously mentioned factors.

LMR33610 JA_curve_soic_4L_SNVSAN3.png
Figure 19. Typical RθJA versus Copper Area for a Four-Layer Board and the HSOIC (DDA) Package
LMR33610 max_output_current_rtja_50.gif
VIN = 12 V VOUT = 5 V
ƒSW = 400 kHz RθJA = 50°C/W
Figure 21. Maximum Output Current versus Ambient Temperature
LMR33610 max_output_current_rtja_30.gif
VIN = 12 V VOUT = 5 V
ƒSW = 400 kHz RθJA = 30°C/W
Figure 20. Maximum Output Current versus Ambient Temperature

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