SNVSCF0 October   2024 LM65680-Q1

ADVANCE INFORMATION  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and Functions
  7. 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
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Descriptions
      1. 7.3.1  Output Voltage Selection
      2. 7.3.2  EN Pin and Use as VIN UVLO
      3. 7.3.3  Device Configuration
      4. 7.3.4  Single-Output Dual-Phase Operation
      5. 7.3.5  Mode Selection
        1. 7.3.5.1 MODE/SYNC Pin Uses for Synchronization
        2. 7.3.5.2 Clock Locking
      6. 7.3.6  Adjustable Switching Frequency
      7. 7.3.7  Dual Random Spread Spectrum (DRSS)
      8. 7.3.8  Internal LDO, VCC UVLO, and BIAS Input
      9. 7.3.9  Bootstrap Voltage (BST Pin)
      10. 7.3.10 Soft Start and Recovery From Dropout
      11. 7.3.11 Safety Features
        1. 7.3.11.1 Power-Good Monitor
        2. 7.3.11.2 Overcurrent and Short-Circuit Protection
        3. 7.3.11.3 Hiccup
        4. 7.3.11.4 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Active Mode
        1. 7.4.2.1 Peak Current Mode Operation
        2. 7.4.2.2 Auto Mode Operation
          1. 7.4.2.2.1 Diode Emulation
        3. 7.4.2.3 FPWM Mode Operation
  9. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Power Train Components
        1. 8.1.1.1 Buck Inductor
        2. 8.1.1.2 Output Capacitors
        3. 8.1.1.3 Input Capacitors
        4. 8.1.1.4 EMI Filter
      2. 8.1.2 Error Amplifier and Compensation
      3. 8.1.3 Maximum Ambient Temperature
        1. 8.1.3.1 Derating Curves
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Inductor Selection
        2. 8.2.2.2 Output Capacitors
        3. 8.2.2.3 Feed-forward Capacitor (CFF)
        4. 8.2.2.4 Input Capacitor Selection
        5. 8.2.2.5 Choosing the Switching Frequency
        6. 8.2.2.6 Setting the Output Voltage
        7. 8.2.2.7 Compensation Components
        8. 8.2.2.8 CBST
        9. 8.2.2.9 External UVLO
      3. 8.2.3 Application Curves
    3. 8.3 Best Design Practices
    4. 8.4 Power Supply Recommendations
    5. 8.5 Layout
      1. 8.5.1 Layout Guidelines
        1. 8.5.1.1 Ground and Thermal Considerations
      2. 8.5.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Development Support
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
        1. 9.2.1.1 PCB Layout Resources
        2. 9.2.1.2 Thermal Design Resources
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information
    1. 11.1 Tape and Reel Information

Package Options

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

7.3.2 EN Pin and Use as VIN UVLO

Start-up and shutdown are controlled by the EN input. This input features precision thresholds, allowing the use of an external voltage divider to provide an adjustable input Undervoltage Lockout (UVLO). Applying a voltage greater than about 0.9V causes the device to enter standby mode, powering the internal VCC, but not producing an output voltage. Increasing the EN voltage to VEN_TH_R fully enables the device, allowing the device to enter start-up mode and begin the soft-start period. When the EN input is brought below VEN_TH_F, the regulator stops switching and enters standby mode. Further decrease in the EN voltage to below 0.9V completely shuts down the device, providing a shutdown current of less than 0.65μA (typical). The EN input can be connected directly to VIN if this feature is not needed. The enable must not float as floating the pin forces the device off. The values for the various EN thresholds can be found in the Electrical Characteristics table. Keep in mind that the internal VIN UVLO overrides the EN input. The device does not start up unless the input voltage is above VINUVLO(R). Conversely, the device shuts down when the input voltage falls bellow VINUVLO(F).

LM65680-Q1 VIN UVLO Using the EN Pin Figure 7-2 VIN UVLO Using the EN Pin

In some cases, an input UVLO level different than that provided internal to the device is needed. This feature can be used for special sequencing or to prevent input voltage oscillations caused by excessively long power cables. External UVLO can be accomplished by using the circuit shown in Figure 7-2. The input voltage at which the device turns on is designated as VON while the turn-off voltage is VOFF. The current in the divider must be greater than the current into the EN input (IEN_LKG) to preserve accuracy. Values for RENB between 10kΩ and 50kΩ are reasonable. Then, Equation 2 is used to calculate RENT and Equation 3 is used to calculate VOFF.

Equation 2. R E N T = R E N B × V O N V E N _ T H _R - 1
Equation 3. V O F F = V O N × V E N _ T H _F V E N _ T H _R

where

  • VON = VIN turn-on voltage
  • VOFF = VIN turn-off voltage