SNVSB14C April   2018  – October 2021 LM5036

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and 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
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  High-Voltage Start-Up Regulator
      2. 7.3.2  Undervoltage Lockout (UVLO)
      3. 7.3.3  Reference Regulator
      4. 7.3.4  Oscillator, Synchronized Input
      5. 7.3.5  Voltage-Mode Control
      6. 7.3.6  Primary-Side Gate Driver Outputs (LSG and HSG)
      7. 7.3.7  Half-Bridge PWM Scheme
      8. 7.3.8  Maximum Duty Cycle Operation
      9. 7.3.9  Pre-Biased Start-Up Process
        1. 7.3.9.1 Primary FETs Soft-Start Process
        2. 7.3.9.2 Synchronous Rectifier (SR) Soft-Start Process
      10. 7.3.10 Zero Duty Cycle Operation
      11. 7.3.11 Enhanced Cycle-by-Cycle Current Limiting with Pulse Matching
      12. 7.3.12 Reverse Current Protection
      13. 7.3.13 CBC Threshold Accuracy
      14. 7.3.14 Hiccup Mode Protection
      15. 7.3.15 Hiccup Mode Blanking
      16. 7.3.16 Over-Temperature Protection (OTP)
      17. 7.3.17 Over-Voltage / Latch (ON_OFF Pin)
      18. 7.3.18 Auxiliary Constant On-Time Control
      19. 7.3.19 Auxiliary On-Time Generator
      20. 7.3.20 Auxiliary Supply Current Limiting
      21. 7.3.21 Auxiliary Primary Output Capacitor Ripple
      22. 7.3.22 Auxiliary Ripple Configuration and Control
      23. 7.3.23 Asynchronous Mode Operation of Auxiliary Supply
    4. 7.4 Device Functional Modes
  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  Input Transient Protection
        3. 8.2.2.3  Level-Shift Detection Circuit
        4. 8.2.2.4  Applications with VIN > 100-V
        5. 8.2.2.5  Applications without Pre-Biased Start-Up Requirement
        6. 8.2.2.6  UVLO Voltage Divider Selection
        7. 8.2.2.7  Over Voltage, Latch (ON_OFF Pin) Voltage Divider Selection
        8. 8.2.2.8  SS Capacitor
        9. 8.2.2.9  SSSR Capacitor
        10. 8.2.2.10 Half-Bridge Power Stage Design
        11. 8.2.2.11 Current Limit
        12. 8.2.2.12 Auxiliary Transformer
        13. 8.2.2.13 Auxiliary Feedback Resistors
        14. 8.2.2.14 RON Resistor
        15. 8.2.2.15 VIN Pin Capacitor
        16. 8.2.2.16 Auxiliary Primary Output Capacitor
        17. 8.2.2.17 Auxiliary Secondary Output Capacitor
        18. 8.2.2.18 Auxiliary Feedback Ripple Circuit
        19. 8.2.2.19 Auxiliary Secondary Diode
        20. 8.2.2.20 VCC Diode
        21. 8.2.2.21 Opto-Coupler Interface
        22. 8.2.2.22 Full-Bridge Converter Applications
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Custom Design With WEBENCH® Tools
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
        1. 11.2.1.1 Receiving Notification of Documentation Updates
    3. 11.3 Support 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

7.3.18 Auxiliary Constant On-Time Control

Figure 7-22 shows a block diagram of the constant on-time (COT) controlled fly-buck converter. The LM5036 device integrates an N-channel high-side MOSFET and associated high-voltage gate driver. The gate driver circuit works in conjunction with an external bootstrap capacitor and an internal high voltage diode. A 0.01-µF ceramic capacitor connected between the BST_AUX pin and SW_AUX pin provides the voltage to the driver during the on-time. During each off-time, the SW_AUX pin is at approximately 0-V, and the bootstrap capacitor charges from VCC through the internal diode. The minimum off-timer ensures a minimum time in each cycle to recharge the bootstrap capacitor. The LM5036 device also provides an internal N-channel SR MOSFET and associated driver. This MOSFET provides a path for the inductor current to flow when the high-side MOSFET is turned off.

The integrated auxiliary supply employs constant on-time (COT) hysteretic control which provides excellent transient response and ease of use. The control principle is based on a comparator and a one-shot on-timer, with the output voltage feedback (FB_AUX) compared to an internal reference. If the feedback voltage is below the reference the internal buck switch is switched on for the one-shot timer period, which is a function of the input voltage and the on-time resistor (RON). Following the on-time the switch remains off until the FB_AUX voltage falls below the reference, and the forced minimum off-time has expired. When the feedback voltage falls below the reference and the minimum off-time one-shot period expires, the high-side buck switch is then turned on for another on-time one-shot period. This will continue until regulation is achieved.

GUID-3DEA5793-3F0F-4F6F-9764-162347F0781F-low.gifFigure 7-22 COT Controlled Fly-Buck Auxiliary Supply Circuitry

In a fly-buck converter, the low-side SR MOSFET is on when the high-side switch is off. The inductor current ramps up when the high-side switch is on and ramps down when the low-side switch is on.

The switching frequency remains relatively constant with load and line variations. Use Equation 31 to calculate the switching frequency of the auxiliary supply.

Equation 31. GUID-99EA4655-6077-459A-B888-869BA4C0B3DC-low.gif

where

  • VAUX1 is the primary output voltage of the auxiliary supply.

Two external resistor values set the value of VAUX1. This regulation of the output voltage depends on ripple voltage at the feedback input, requiring a minimum amount of ESR for the output capacitor (CAUX1). A minimum of 25-mV of ripple voltage at the feedback pin is required for stable operation of the auxiliary supply. The Section 7.3.22 section describes auxiliary ripple circuit configuration.