SNVSAN3F August   2017  – November 2020 LMR33630


  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 System Characteristics
    8. 7.8 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Power-Good Flag Output
      2. 8.3.2 Enable and Start-up
      3. 8.3.3 Current Limit and Short Circuit
      4. 8.3.4 Undervoltage Lockout and Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Auto Mode
      2. 8.4.2 Dropout
      3. 8.4.3 Minimum Switch On-Time
  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.  Custom Design With WEBENCH® Tools
        2.  Choosing the Switching Frequency
        3.  Setting the Output Voltage
        4.  Inductor Selection
        5.  Output Capacitor Selection
        6.  Input Capacitor Selection
        7.  CBOOT
        8.  VCC
        9.  CFF Selection
        10. External UVLO
        11. Maximum Ambient Temperature
      3. 9.2.3 Application Curves
    3. 9.3 What to Do and What Not to Do
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Ground and Thermal Considerations
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
        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 Support Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • RNX|12
  • DDA|8
Thermal pad, mechanical data (Package|Pins)
Orderable Information

Auto Mode

In auto mode, the device moves between PWM and PFM as the load changes. At light loads, the regulator operates in PFM. At higher loads, the mode changes to PWM. The load current for which the device moves from PFM to PWM can be found in Section 9.2.3. The output current at which the device changes modes depends on the input voltage, inductor value, and the nominal switching frequency. For output currents above the curve, the device is in PWM mode. For currents below the curve, the device is in PFM. The curves apply for and the BOM shown in Table 9-4 and a nominal switching frequency of 400 kHz. At higher switching frequencies, the load at which the mode change occurs is greater. For applications where the switching frequency must be known for a given condition, the transition between PFM and PWM must be carefully tested before the design is finalized.

In PWM mode, the regulator operates as a constant frequency converter using PWM to regulate the output voltage. While operating in this mode, the output voltage is regulated by switching at a constant frequency and modulating the duty cycle to control the power to the load. This provides excellent line and load regulation and low output voltage ripple.

In PFM, the high-side MOSFET is turned on in a burst of one or more pulses to provide energy to the load. The duration of the burst depends on how long it takes the inductor current to reach IPEAK-MIN. The periodicity of these bursts is adjusted to regulate the output, while diode emulation (DEM) is used to maximize efficiency (see the Glossary). This mode provides high light-load efficiency by reducing the amount of input supply current required to regulate the output voltage at light loads. PFM results in very good light-load efficiency, but also yields larger output voltage ripple and variable switching frequency. Also, a small increase in output voltage occurs at light loads. The actual switching frequency and output voltage ripple depends on the input voltage, output voltage, and load. Typical switching waveforms in PFM and PWM are shown in Figure 8-7 and Figure 8-8.

See Section 9.2.3 for output voltage variation with load in auto mode.

GUID-4AA4FB10-E120-4EFE-9233-64ACE47358CD-low.gifFigure 8-7 Typical PFM Switching Waveforms VIN = 12 V, VOUT = 5 V, IOUT = 10 mA
GUID-96991E54-11A6-46F9-ADA5-BB9FF83F63E8-low.gifFigure 8-8 Typical PWM Switching Waveforms VIN = 12 V, VOUT = 5 V, IOUT = 3 A, ƒS = 400 kHz