SNVSBA0D February   2020  – August 2021 LM61480-Q1 , LM61495-Q1 , LM62460-Q1


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and 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 Switching Characteristics
    8. 7.8 System Characteristics
    9. 7.9 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Output Voltage Selection
      2. 8.3.2  Enable EN Pin and Use as VIN UVLO
      3. 8.3.3  SYNC/MODE Uses for Synchronization
      4. 8.3.4  Clock Locking
      5. 8.3.5  Adjustable Switching Frequency
      6. 8.3.6  RESET Output Operation
      7. 8.3.7  Internal LDO, VCC UVLO, and BIAS Input
      8. 8.3.8  Bootstrap Voltage and VCBOOT-UVLO (CBOOT Pin)
      9. 8.3.9  Adjustable SW Node Slew Rate
      10. 8.3.10 Spread Spectrum
      11. 8.3.11 Soft Start and Recovery From Dropout
      12. 8.3.12 Overcurrent and Short Circuit Protection
      13. 8.3.13 Hiccup
      14. 8.3.14 Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
      2. 8.4.2 Standby Mode
      3. 8.4.3 Active Mode
        1. Peak Current Mode Operation
        2. Auto Mode Operation
          1. Diode Emulation
        3. FPWM Mode Operation
        4. Minimum On-time (High Input Voltage) Operation
        5. Dropout
        6. Recovery from Dropout
        7. Other Fault Modes
  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.  Choosing the Switching Frequency
        2.  Setting the Output Voltage
        3.  Inductor Selection
        4.  Output Capacitor Selection
        5.  Input Capacitor Selection
        6.  BOOT Capacitor
        7.  BOOT Resistor
        8.  VCC
        9.  CFF and RFF Selection
        10. RSPSP Selection
        11. RT Selection
        12. RMODE Selection
        13. External UVLO
        14. Maximum Ambient Temperature
      3. 9.2.3 Application Curves
  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 Third-Party Products Disclaimer
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Glossary
    6. 12.6 Electrostatic Discharge Caution
  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 LM6x4xx-Q1 dissipates internal power while operating. The effect of this power dissipation is to raise the internal temperature of the converter above ambient temperature. The internal die temperature (TJ) is a function of the following:

  • Ambient temperature
  • Power loss
  • Effective thermal resistance, RθJA of the device
  • PCB layout
The maximum internal die temperature for the LM6x4xx-Q1 must be limited to 150°C. This establishes a limit on the maximum device power dissipation and, therefore, the load current. Equation 8 shows the relationships between the important parameters. 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 the Application Curves section. 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 Section 7.4 is not valid for design purposes and must not be used to estimate the thermal performance of the device in a real application. The values reported in the Section 7.4 table were measured under a specific set of conditions that are rarely obtained in an actual application.

Equation 8. GUID-F61A2C5D-0A01-45B4-82A1-5051FF2999D7-low.gif


  • η = efficiency
  • TA = ambient temperature
  • TJ = junction temperature
  • RθJA = the effective thermal resistance of the IC junction to the air, mainly through the PCB

The effective RθJA is a critical parameter and depends on many factors (just to mention a few of the most critical parameters:

  • Power dissipation
  • Air temperature
  • Airflow
  • PCB area
  • Copper heat-sink area
  • Number of thermal vias under or near the package
  • Adjacent component placement
Due to the ultra-miniature size of the VQFN (RNX) package, a die-attach pad is not available, requiring most of the heat to flow from the pins to the board. This means that this package exhibits a somewhat large RθJA value when the layout does not allow for heat to flow from the pins. A typical curve of maximum output current versus ambient temperature is shown in Figure 9-3 and Figure 9-4 for a good thermal layout. This data was taken on the LM61495RPHEVM evaluation board with a device and PCB combination, giving an RθJA of about 21.6°C/W. 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.

VIN = 13.5 VVOUT = 5 V
ƒSW = 400 kHzRθJA = 22°C/W
Figure 9-3 Maximum Output Current versus Ambient Temperature
VIN = 13.5 VVOUT = 5 V
ƒSW = 2.2 MHzRθJA = 22°C/W
Figure 9-4 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: