SNVSCT4B April   2025  – October 2026 LM72880-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Related Products
  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 Timing Requirements for the Serial Control Bus
    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  Input Voltage Range (VIN)
      2. 7.3.2  High-Voltage Bias Supply Regulators (VCC, VDDA)
      3. 7.3.3  Enable (EN/UVLO)
      4. 7.3.4  Switching Frequency
      5. 7.3.5  Dual Random Spread Spectrum (DRSS)
      6. 7.3.6  Soft Start
      7. 7.3.7  Output Voltage and Output Voltage Slew Rate
      8. 7.3.8  Minimum Controllable On-Time
      9. 7.3.9  Dual Loop Architecture
        1. 7.3.9.1 Voltage Loop Error Amplifier
        2. 7.3.9.2 Current Loop Error Amplifier
      10. 7.3.10 Programmable OVP
      11. 7.3.11 Programmable ILIM
      12. 7.3.12 IOUT Monitor
      13. 7.3.13 Cable Drop Compensation
      14. 7.3.14 Slope Compensation
      15. 7.3.15 Shunt Current Sensing
      16. 7.3.16 Hiccup Mode Current Limiting
      17. 7.3.17 Device Configuration (CNFG)
      18. 7.3.18 Pulse Frequency Modulation (PFM) / Synchronization
      19. 7.3.19 Out-of-Audio Operation
      20. 7.3.20 Thermal Shutdown (TSD)
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Standby Mode
      3. 7.4.3 Ready Mode
      4. 7.4.4 Active Mode
      5. 7.4.5 Sleep Mode
    5. 7.5 Programming
      1. 7.5.1 I2C Bus Operation
      2. 7.5.2 Clock Stretching
      3. 7.5.3 Data Transfer Formats
      4. 7.5.4 Single READ from a Defined Register Address
      5. 7.5.5 Sequential READ Starting from a Defined Register Address
      6. 7.5.6 Single WRITE to a Defined Register Address
      7. 7.5.7 Sequential WRITE Starting at a Defined Register Address
  9. 8 LM72880-Q1 Registers
  10. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Power Train Components
        1. 9.1.1.1 Buck Inductor
        2. 9.1.1.2 Output Capacitors
        3. 9.1.1.3 Input Capacitors
        4. 9.1.1.4 EMI Filter
      2. 9.1.2 Error Amplifier and Compensation
      3. 9.1.3 Maximum Ambient Temperature
        1. 9.1.3.1 Derating Curves
    2. 9.2 Typical Application
      1. 9.2.1 High Efficiency, Wide Input, 400kHz, Synchronous Buck Regulator
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Custom Design With WEBENCH® Tools
          2. 9.2.1.2.2 Buck Inductor
          3. 9.2.1.2.3 Current-Sense Resistance
          4. 9.2.1.2.4 Output Capacitors
          5. 9.2.1.2.5 Input Capacitors
          6. 9.2.1.2.6 Compensation Components
        3. 9.2.1.3 Application Curves
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
        1. 9.4.1.1 Thermal Design and Layout
      2. 9.4.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Development Support
        1. 10.1.1.1 Custom Design With WEBENCH® Tools
    2. 10.2 Documentation Support
      1. 10.2.1 Related Documentation
        1. 10.2.1.1 PCB Layout Resources
        2. 10.2.1.2 Thermal Design Resources
    3. 10.3 Receiving Notification of Documentation Updates
    4. 10.4 Support Resources
    5. 10.5 Trademarks
    6. 10.6 Electrostatic Discharge Caution
    7. 10.7 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information

9.1.3 Maximum Ambient Temperature

As with any power conversion device, the LM72880-Q1 dissipates internal power while operating. The effect of this power dissipation is the rise of 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 LM72880-Q1 must be limited to 150°C. This limit establishes a limit on the maximum device power dissipation and, therefore, the load current. Equation 27 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 LM72880-Q1 quick-start design tool. Alternatively, the EVM can be adjusted to match the desired application requirements and the efficiency can be measured directly.

Equation 27. I O U T M A X = ( T J - T A ) R θ J A × η ( 1 - η ) × 1 V O U T

where

  • 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 correct value of RθJA is more difficult to estimate. As stated in the Semiconductor and IC Package Thermal Metrics application note the JESD 51-7 value of RθJA given in Thermal Information is not valid for design purposes and must not be used to estimate the thermal performance of the device in a real application. The JESD 51-7 values reported in Thermal Information are measured under a specific set of conditions that are rarely obtained in an actual application.

The effective RθJA is a critical parameter and depends on many factors. The following are 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

Typical curves of maximum output current versus ambient temperature are shown in Derating Curves for a good thermal layout.

Use Thermal Design Resources as a guide for thermal PCB design and estimating RθJA for a given application environment.