SNVS523G September   2007  – January 2018 LM3103

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Typical Application Schematic
  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 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Functional Block Diagram
    2. 7.2 Feature Description
      1. 7.2.1  COT Control Circuit Overview
      2. 7.2.2  Startup Regulator (VCC)
      3. 7.2.3  Regulation Comparator
      4. 7.2.4  Zero Coil Current Detect
      5. 7.2.5  Over-Voltage Comparator
      6. 7.2.6  ON-Time Timer, Shutdown
      7. 7.2.7  Current Limit
      8. 7.2.8  N-Channel MOSFET and Driver
      9. 7.2.9  Soft-Start
      10. 7.2.10 Thermal Protection
  8. 8 Applications and Implementation
    1. 8.1 Application Information
      1. 8.1.1 External Components
  9. 9 Device and Documentation Support
    1. 9.1 Receiving Notification of Documentation Updates
    2. 9.2 Community Resources
    3. 9.3 Trademarks
    4. 9.4 Electrostatic Discharge Caution
    5. 9.5 Glossary
  10. 10Mechanical, Packaging, and Orderable Information

Package Options

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

7.2.7 Current Limit

Current limit detection is carried out during the off-time by monitoring the re-circulating current through the synchronous MOSFET. Referring to the Functional Block Diagram, when the main MOSFET is turned off, the inductor current flows through the load, the PGND pin and the internal synchronous MOSFET. If this current exceeds 0.9 A, the current limit comparator toggles, and as a result the start of the next on-time period is disabled. The next switching cycle starts when the re-circulating current falls back below 0.9 A (and the voltage at the FB pin is below 0.6 V). The inductor current is monitored during the on-time of the synchronous MOSFET. As long as the inductor current exceeds 0.9 A, the main MOSFET will remain inhibited to achieve current limit. The operating frequency is lower during current limit owing to a longer off-time.

Figure 20 illustrates an inductor current waveform. On average, the output current IOUT is the same as the inductor current IL, which is the average of the rippled inductor current. In case of current limit (the current limit portion of Figure 20), the next on-time will not initiate until that the current drops below 0.9 A (assume the voltage at the FB pin is lower than 0.6 V). During each on-time the current ramps up an amount equal to:

Equation 6. LM3103 30029727.gif

During current limit, the LM3103 operates in a constant current mode with an average output current IOUT(CL) equal to 0.9 A + ILR / 2.

LM3103 30029728.pngFigure 20. Inductor Current - Current Limit Operation