SNVSBB5B September   2019  – September 2020 LMR36503-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD (Automotive) 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 Switching Characteristics
    8. 7.8 System Characteristics
    9. 7.9 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Enable, Start-up and Shutdown
      2. 8.3.2  External CLK SYNC (with MODE/SYNC)
        1. 8.3.2.1 Pulse-Dependent MODE/SYNC Pin Control
      3. 8.3.3  Adjustable Switching Frequency (with RT)
      4. 8.3.4  Power-Good Output Operation
      5. 8.3.5  Internal LDO, VCC UVLO, and VOUT/BIAS Input
      6. 8.3.6  Bootstrap Voltage and VCBOOT-UVLO (CBOOT Terminal)
      7. 8.3.7  Output Voltage Selection
      8. 8.3.8  Soft Start and Recovery from Dropout
        1. 8.3.8.1 Recovery from Dropout
      9. 8.3.9  Current Limit and Short Circuit
      10. 8.3.10 Thermal Shutdown
      11. 8.3.11 Input Supply Current
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
      2. 8.4.2 Standby Mode
      3. 8.4.3 Active Mode
        1. 8.4.3.1 CCM Mode
        2. 8.4.3.2 Auto Mode - Light Load Operation
          1. 8.4.3.2.1 Diode Emulation
          2. 8.4.3.2.2 Frequency Reduction
        3. 8.4.3.3 FPWM Mode - Light Load Operation
        4. 8.4.3.4 Minimum On-time (High Input Voltage) Operation
        5. 8.4.3.5 Dropout
  9. 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. 9.2.2.1 Choosing the Switching Frequency
        2. 9.2.2.2 Setting the Output Voltage
          1. 9.2.2.2.1 FB for Adjustable Output
        3. 9.2.2.3 Inductor Selection
        4. 9.2.2.4 Output Capacitor Selection
        5. 9.2.2.5 Input Capacitor Selection
        6. 9.2.2.6 CBOOT
        7. 9.2.2.7 VCC
        8. 9.2.2.8 CFF Selection
          1. 9.2.2.8.1 External UVLO
        9. 9.2.2.9 Maximum Ambient Temperature
      3. 9.2.3 Application Curves
    3. 9.3 What to Do and What Not to Do
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Ground and Thermal Considerations
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

8.3.2.1 Pulse-Dependent MODE/SYNC Pin Control

Most systems that require more than a single mode of operation from the LMR36503-Q1 are controlled by digital circuitry such as a microprocessor. These systems can generate dynamic signals easily but have difficulty generating multi-level signals. Pulse-Dependent MODE/SYNC pin control is useful with these systems. To initiate Pulse-Dependent MODE/SYNC pin control, a valid sync signal must be applied. Table 8-1 shows a summary of the pulse dependent mode selection settings.

Table 8-1 Pulse-Dependent Mode Selection Settings
MODE/SYNC INPUT MODE
> VMODE_H FPWM with Spread Spectrum factory setting
< VMODE_L Auto Mode with Spread Spectrum factory setting
Synchronization Clock SYNC Mode

Figure 8-4 shows the transition between AUTO Mode and FPWM Mode while in Pulse-Dependent MODE/SYNC control. The LMR36503-Q1 transitions to a new mode of operation after the time, tMODE. Figure 8-4 and Figure 8-5 show the details.

GUID-32E80C25-CC68-4F3C-83BE-CA4E6365186B-low.gifFigure 8-4 Transition from Auto Mode and FPWM Mode

If MODE/SYNC voltage remains constant longer than tMODE, the LMR36503-Q1 enters either Auto mode or FPWM mode with spread spectrum turned on (if factory setting is enabled) and MODE/SYNC continues to operate in Pulse-Dependent scheme.

GUID-649CE5C6-E3CF-4408-8F9F-0C85C3E4B7BF-low.gifFigure 8-5 Transition from SYNC Mode to Auto Mode
GUID-6E43A49E-F1B0-40A5-9308-C53F7AC87DF0-low.gifFigure 8-6 Transition from SYNC Mode to FPWM Mode