SNVS485I June   2007  – September 2018 LM2735

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Boost Application Circuit
      2.      Efficiency vs Load Current VO = 12 V
  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: LM2735
    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 Overview
      1. 7.1.1 Theory of Operation
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Current Limit
      2. 7.3.2 Thermal Shutdown
      3. 7.3.3 Soft Start
      4. 7.3.4 Compensation
    4. 7.4 Device Functional Modes
      1. 7.4.1 Enable Pin and Shutdown Mode
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1  LM2735X SOT-23 Design Example 1
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Custom Design With WEBENCH® Tools
          2. 8.2.1.2.2 Inductor Selection
          3. 8.2.1.2.3 Input Capacitor
          4. 8.2.1.2.4 Output Capacitor
          5. 8.2.1.2.5 Setting the Output Voltage
        3. 8.2.1.3 Application Curves
      2. 8.2.2  LM2735Y SOT-23 Design Example 2
      3. 8.2.3  LM2735X WSON Design Example 3
      4. 8.2.4  LM2735Y WSON Design Example 4
      5. 8.2.5  LM2735Y MSOP-PowerPAD Design Example 5
      6. 8.2.6  LM2735X SOT-23 Design Example 6
      7. 8.2.7  LM2735Y SOT-23 Design Example 7
      8. 8.2.8  LM2735X SOT-23 Design Example 8
      9. 8.2.9  LM2735Y SOT-23 Design Example 9
      10. 8.2.10 LM2735X WSON Design Example 10
      11. 8.2.11 LM2735Y WSON Design Example 11
      12. 8.2.12 LM2735X WSON SEPIC Design Example 12
      13. 8.2.13 LM2735Y MSOP-PowerPAD SEPIC Design Example 13
      14. 8.2.14 LM2735X SOT-23 LED Design Example 14
      15. 8.2.15 LM2735Y WSON FlyBack Design Example 15
      16. 8.2.16 LM2735X SOT-23 LED Design Example 16 VRAIL > 5.5 V Application
      17. 8.2.17 LM2735X SOT-23 LED Design Example 17 Two-Input Voltage Rail Application
      18. 8.2.18 SEPIC Converter
        1. 8.2.18.1 Detailed Design Procedure
          1. 8.2.18.1.1 SEPIC Design Guide
          2. 8.2.18.1.2 Small Ripple Approximation
          3. 8.2.18.1.3 Steady State Analysis With Loss Elements
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 WSON Package
    2. 10.2 Layout Examples
    3. 10.3 Thermal Considerations
      1. 10.3.1 Definitions
      2. 10.3.2 PCB Design With Thermal Performance in Mind
      3. 10.3.3 LM2735 Thermal Models
      4. 10.3.4 Calculating Efficiency, and Junction Temperature
        1. 10.3.4.1 Example Efficiency Calculation
      5. 10.3.5 Calculating RθJA and RΨJC
        1. 10.3.5.1 Procedure
        2. 10.3.5.2 Example From Previous Calculations
  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. 11.1.2.1 Custom Design With WEBENCH® Tools
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    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

Package Options

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

7.1.1 Theory of Operation

The LM2735 is a constant-frequency PWM boost regulator IC that delivers a minimum of 2.1 A peak switch current. The regulator has a preset switching frequency of either 520 kHz or 1.6 MHz. This high frequency allows the device to operate with small surface mount capacitors and inductors, resulting in a DC-DC converter that requires a minimum amount of board space. The LM2735 is internally compensated, so it is simple to use, and requires few external components. The device uses current-mode control to regulate the output voltage. The following operating description of the LM2735 refers to the simplified internal block diagram (Functional Block Diagram), the simplified schematic (Figure 13), and its associated waveforms (Figure 14). The LM2735 supplies a regulated output voltage by switching the internal NMOS control switch at constant frequency and variable duty cycle. A switching cycle begins at the falling edge of the reset pulse generated by the internal oscillator. When this pulse goes low, the output control logic turns on the internal NMOS control switch. During this on-time, the SW pin voltage (VSW) decreases to approximately GND, and the inductor current (IL) increases with a linear slope. IL is measured by the current sense amplifier, which generates an output proportional to the switch current. The sensed signal is summed with the corrective ramp of the regulator and compared to the error amplifier’s output, which is proportional to the difference between the feedback voltage and VREF. When the PWM comparator output goes high, the output switch turns off until the next switching cycle begins. During the switch off-time, inductor current discharges through diode D1, which forces the SW pin to swing to the output voltage plus the forward voltage (VD) of the diode. The regulator loop adjusts the duty cycle (D) to maintain a constant output voltage .

LM2735 20215819.gifFigure 13. Simplified Schematic
LM2735 20215820.gifFigure 14. Typical Waveforms