SNVS852D June   2012  – August 2018 LMZ20502


  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      Simplified Schematic
      2.      Typical Efficiency for VOUT = 1.8 V Auto Mode
  4. Revision History
  5. Pin Configuration and Functions
    1.     Pin 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 System Characteristics
    7. 6.7 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Nano Scale Package
      2. 7.3.2 Internal Synchronous Rectifier
      3. 7.3.3 Current Limit Protection
      4. 7.3.4 Start-Up
      5. 7.3.5 Dropout Behavior
      6. 7.3.6 Power Good Flag Function
      7. 7.3.7 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 PWM Operation
      2. 7.4.2 PFM Operation
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Detailed Design Procedure
        1. Custom Design With WEBENCH® Tools
        2. Setting The Output Voltage
        3. Output and Feed-Forward Capacitors
        4. Input Capacitors
        5. Maximum Ambient Temperature
        6. Options
      2. 8.2.2 Application Curves
    3. 8.3 Do's and Don'ts
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Soldering Information
  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. Custom Design With WEBENCH® Tools
      3. 11.1.3 Documentation Support
        1. Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information
    1. 12.1 Tape and Reel Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • SIL|8
Thermal pad, mechanical data (Package|Pins)
Orderable Information

Maximum Ambient Temperature

As with any power conversion device, the LMZ20502 will dissipate 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 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 LMZ20502 is 125°C, thus establishing a limit on the maximum device power dissipation and therefore load current at high ambient temperatures. Equation 3 shows the relationships between the important parameters.

Equation 3. LMZ20502 output_current_eq2.gif

It is easy to see that larger ambient temperatures and larger values of RθJA will reduce the maximum available output current. As stated in SPRA953, the values given in the Thermal Information table are 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 never obtain in an actual application. The effective RθJA is a critical parameter and depends on many factors such as power dissipation, air temperature, PCB area, copper heatsink area, air flow, and adjacent component placement. The resources found in Table 3 can be used as a guide to estimate the RθJA for a given application environment. A typical example of RθJA versus copper board area is shown in Figure 18 . The copper area in this graph is that for each layer; the inner layers are 1 oz. (35µm). An RθJA of 44°C/W is the approximate value for the LMZ20502 evaluation board. The efficiency found in the equation, η, should be taken at the elevated ambient temperature. For the LMZ20502 the efficiency is about two to three percent lower at high temperatures. Therefore, a slightly lower value than the typical efficiency can be used in the calculation. In this way Equation 3 can be used to estimate the maximum output current for a given ambient, or to estimate the maximum ambient for a given load current.

A typical curve of maximum load current vs. ambient temperature is shown in Figure 19. This graph assumes a RθJA of 44°C/W and an input voltage of 5 V.

LMZ20502 D012_LMZ21701_PACKAGE_THERMAL_VS_PCB_SNVS853.gifFigure 18. RθJA versus Copper Board Area
LMZ20502 de_rate2_snvs852.pngFigure 19. Maximum Output Current Vs. Ambient Temperature, RθJA = 44°C/W, VIN = 5 V