SNVSAO6C September   2017  – March 2018 LMZM33603

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
    1.     Simplified Schematic
  3. 3 Description
    1.     Safe Operating Area
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 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 Switching Characteristics
    7. 6.7 Typical Characteristics (VIN = 5 V)
    8. 6.8 Typical Characteristics (VIN = 12 V)
    9. 6.9 Typical Characteristics (VIN = 24 V)
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Adjusting the Output Voltage
      2. 7.3.2  Feed-Forward Capacitor, CFF
      3. 7.3.3  Output Current vs Output Voltage
      4. 7.3.4  Voltage Dropout
      5. 7.3.5  Switching Frequency (RT)
      6. 7.3.6  Synchronization (SYNC)
      7. 7.3.7  Input Capacitors
      8. 7.3.8  Output Capacitors
      9. 7.3.9  Output On/Off Enable (EN)
      10. 7.3.10 Programmable Undervoltage Lockout (UVLO)
      11. 7.3.11 Power Good (PGOOD)
      12. 7.3.12 Overcurrent Protection (OCP)
      13. 7.3.13 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Active Mode
      2. 7.4.2 Shutdown Mode
  8. 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 Output Voltage Setpoint
        3. 8.2.2.3 Feed-Forward Capacitor (CFF)
        4. 8.2.2.4 Setting the Switching Frequency
        5. 8.2.2.5 Input Capacitors
        6. 8.2.2.6 Output Capacitor Selection
        7. 8.2.2.7 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Examples
    3. 10.3 Theta JA vs PCB Area
    4. 10.4 EMI
      1. 10.4.1 EMI Plots
    5. 10.5 Package Specifications
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
      2. 11.1.2 Custom Design With WEBENCH® Tools
    2. 11.2 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Community Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information
    1. 12.1 Tape and Reel Information

7.3.4 Voltage Dropout

Voltage dropout is the difference between the input voltage and output voltage that is required to maintain output voltage regulation while providing the rated output current.

To ensure the LMZM33603 maintains output voltage regulation at the recommended switching frequency, over the operating temperature range, the following requirements apply:

For output voltages ≤ 5 V, the minimum VIN is 4 V or (VOUT + 1.5 V), whichever is greater.

For output voltages > 5 V, the minimum VIN is (1.3 × VOUT).

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However, if fixed switching frequency operation is not required, the LMZM33603 operates in a frequency foldback mode when the dropout voltage is less than the recommendations above. Frequency foldback reduces the switching frequency to allow the output voltage to maintain regulation as input voltage decreases. Figure 20 through Figure 25 show typical dropout voltage and frequency foldback curves for 3.3 V, 5 V, and 12 V outputs at TA = 25°C. (Note: As ambient temperature increases, dropout voltage and frequency foldback occur at higher input voltage.)

LMZM33603 D017_3AZZtop2.gif
VOUT = 3.3 V fSW = 300 kHz
Figure 20. Voltage Dropout
LMZM33603 D019_3AZZtop2.gif
VOUT = 5 V fSW = 450 kHz
Figure 22. Voltage Dropout
LMZM33603 D021_3AZZtop.gif
VOUT = 12 V fSW = 900 kHz
Figure 24. Voltage Dropout
LMZM33603 D018_3AZZtop.gif
VOUT = 3.3 V fSW = 300 kHz
Figure 21. Frequency Foldback
LMZM33603 D020_3AZZtop.gif
VOUT = 5 V fSW = 450 kHz
Figure 23. Frequency Foldback
LMZM33603 D022_3AZZtop.gif
VOUT = 12 V fSW = 900 kHz
Figure 25. Frequency Foldback