SNVS509F April   2007  – November 2023 LM25116

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Switching Characteristics
    7. 5.7 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 High-Voltage Start-Up Regulator
      2. 6.3.2 Enable
      3. 6.3.3 UVLO
      4. 6.3.4 Oscillator and Sync Capability
      5. 6.3.5 Error Amplifier and PWM Comparator
      6. 6.3.6 Ramp Generator
      7. 6.3.7 Current Limit
      8. 6.3.8 HO Output
      9. 6.3.9 Thermal Protection
    4. 6.4 Device Functional Modes
      1. 6.4.1 Soft Start and Diode Emulation
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1  Timing Resistor
        2. 7.2.2.2  Output Inductor
        3. 7.2.2.3  Current Sense Resistor
        4. 7.2.2.4  Ramp Capacitor
        5. 7.2.2.5  Output Capacitors
        6. 7.2.2.6  Input Capacitors
        7. 7.2.2.7  VCC Capacitor
        8. 7.2.2.8  Bootstrap Capacitor
        9. 7.2.2.9  Soft Start Capacitor
        10. 7.2.2.10 Output Voltage Divider
        11. 7.2.2.11 UVLO Divider
        12. 7.2.2.12 MOSFETs
        13. 7.2.2.13 MOSFET Snubber
        14. 7.2.2.14 Error Amplifier Compensation
        15. 7.2.2.15 Comprehensive Equations
          1. 7.2.2.15.1 Current Sense Resistor and Ramp Capacitor
          2. 7.2.2.15.2 Modulator Transfer Function
          3. 7.2.2.15.3 Error Amplifier Transfer Function
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Receiving Notification of Documentation Updates
    2. 8.2 Support Resources
    3. 8.3 Trademarks
    4. 8.4 Electrostatic Discharge Caution
    5. 8.5 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

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

6.3.8 HO Output

The LM25116 contains a high current, high-side driver and associated high-voltage level shift. This gate driver circuit works in conjunction with an external diode and bootstrap capacitor. A 1-µF ceramic capacitor, connected with short traces between the HB pin and SW pin, is recommended. During the off-time of the high-side MOSFET, the SW pin voltage is approximately –0.5 V and the bootstrap capacitor charges from VCC through the external bootstrap diode. When operating with a high PWM duty cycle, the buck switch is forced off each cycle for 450 ns to ensure that the bootstrap capacitor is recharged.

The LO and HO outputs are controlled with an adaptive deadtime methodology which insures that both outputs are never enabled at the same time. When the controller commands HO to be enabled, the adaptive block first disables LO and waits for the LO voltage to drop below approximately 25% of VCC. HO is then enabled after a small delay. Similarly, when HO turns off, LO waits until the SW voltage has fallen to ½ of VCC. LO is then enabled after a small delay. In the event that SW does not fall within approximately 150 ns, LO is asserted high. This methodology insures adequate dead-time for appropriately sized MOSFETs.

In some applications it may be desirable to slow down the high-side MOSFET turnon time to control switching spikes. This may be accomplished by adding a resistor is series with the HO output to the high-side gate. Values greater than 10 Ω must be avoided so as not to interfere with the adaptive gate drive. Use of an HB resistor for this function must be carefully evaluated so as not cause potentially harmful negative voltage to the high-side driver, and is generally limited to 2.2 Ω maximum.