JAJSOF6 April   2022 LM5013-Q1

PRODUCTION DATA  

  1. 特長
  2. アプリケーション
  3. 概要
  4. Revision History
  5. Pin Configuration and Functions
  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 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Control Architecture
      2. 7.3.2  Internal VCC Regulator and Bootstrap Capacitor
      3. 7.3.3  Regulation Comparator
      4. 7.3.4  Internal Soft Start
      5. 7.3.5  On-Time Generator
      6. 7.3.6  Current Limit
      7. 7.3.7  N-Channel Buck Switch and Driver
      8. 7.3.8  Schottky Diode Selection
      9. 7.3.9  Enable/Undervoltage Lockout (EN/UVLO)
      10. 7.3.10 Power Good (PGOOD)
      11. 7.3.11 Thermal Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Standby Mode
      3. 7.4.3 Active Mode
      4. 7.4.4 Sleep Mode
  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 Custom Design With WEBENCH® Tools
        2. 8.2.2.2 Switching Frequency (RRON)
        3. 8.2.2.3 Buck Inductor (LO)
        4. 8.2.2.4 Schottky Diode (DSW)
        5. 8.2.2.5 Output Capacitor (COUT)
        6. 8.2.2.6 Input Capacitor (CIN)
        7. 8.2.2.7 Type 3 Ripple Network
      3. 8.2.3 Application Curves
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Compact PCB Layout for EMI Reduction
      2. 10.1.2 Feedback Resistors
    2. 10.2 Layout Example
      1. 10.2.1 Thermal Considerations
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
      2. 11.1.2 Development Support
        1. 11.1.2.1 Custom Design With WEBENCH® Tools
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 サポート・リソース
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ(パッケージ|ピン)
サーマルパッド・メカニカル・データ
発注情報

Thermal Considerations

As with any power conversion device, the LM5013-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 following:

  • Ambient temperature
  • Power loss
  • Effective thermal resistance, RθJA, of the device
  • PCB combination

The maximum internal die temperature for the LM5013-Q1 must be limited to 150°C. This establishes a limit on the maximum device power dissipation and, therefore, the load current. Equation 20 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. Note that these curves include the power loss in the inductor. 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 Thermal Information 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. The data given for RθJC(bott) and ΨJT can be useful when determining thermal performance. See the Semiconductor and IC Package Thermal Metrics Application Report for more information and the resources given at the end of this section.

Equation 20. GUID-F61A2C5D-0A01-45B4-82A1-5051FF2999D7-low.gif

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

The LM5013-Q1 features a die attach paddle, or "thermal pad" (EP), 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 can be found in Figure 10-3. The copper area given in the graph is for each layer. The top and bottom layers are 2-oz copper each, while the inner layers are 1 oz. Remember that the data given in this graph is for illustration purposes only, and the actual performance in any given application depends on all of the previously mentioned factors.

Figure 10-3 Typical RΘJA Versus Copper Area

To continue with the design example, assume that the user has an ambient temperature of 70ºC and wishes to estimate the required copper area to keep the device junction temperature below 125ºC, at full load. From the curves in Section 8.2.3, an efficiency of about 92% was found at an input voltage of 48 V with output of 12 V with 1.75-A load. The efficiency will be somewhat less at high junction temperatures, so an efficiency of approximately 90% is assumed. This gives a total loss of about 2.3 W. Subtracting out the conduction loss alone for the inductor and catch diode, the user arrives at a device dissipation of about 1.54 W. With this information, the user can calculate the required RθJA of about 30ºC/W. Based on Figure 10-3, the required copper area is about 40 cm2 for a two-layer PCB.

The engineer's best judgment is to be used if using a lossy inductor, diode, or both in the application, as their large losses can contribute to localized heating of the component, as well, the nearby regulator. As an example, biasing the Schottky diode (DSW) with 1.3-A continuous current (average current for 1.75-A load current) results in approximately 10°C rise in the case temperature of the regulator. This should be "buffered" for in the ambient temperature used in the previous calculation. For more details on these calculations, please see the PCB Thermal Design Tips for Automotive DC/DC Converters Application Note.

The following resources can be used as a guide to optimal thermal PCB design and estimating RθJA for a given application environment: