SNVSBK5A February   2020  – July 2020 LM76005

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  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 Timing Characteristics
    7. 6.7 Switching Characteristics
    8. 6.8 System Characteristics
    9. 6.9 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  Fixed-Frequency, Peak-Current-Mode Control
      2. 7.3.2  Light Load Operation Modes — PFM and FPWM
      3. 7.3.3  Adjustable Output Voltage
      4. 7.3.4  Enable (EN Pin) and UVLO
      5. 7.3.5  Internal LDO, VCC UVLO, and Bias Input
      6. 7.3.6  Soft Start and Voltage Tracking (SS/TRK)
      7. 7.3.7  Adjustable Switching Frequency (RT) and Frequency Synchronization
      8. 7.3.8  Minimum On-Time, Minimum Off-Time, and Frequency Foldback at Dropout Conditions
      9. 7.3.9  Bootstrap Voltage and VBOOT UVLO (BOOT Pin)
      10. 7.3.10 Power Good and Overvoltage Protection (PGOOD)
      11. 7.3.11 Overcurrent and Short-Circuit Protection
      12. 7.3.12 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Standby Mode
      3. 7.4.3 Active Mode
      4. 7.4.4 CCM Mode
      5. 7.4.5 DCM Mode
      6. 7.4.6 Light Load Mode
      7. 7.4.7 Foldback Mode
      8. 7.4.8 Forced Pulse-Width-Modulation Mode
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      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  Output Voltage Setpoint
        3. 8.2.2.3  Switching Frequency
        4. 8.2.2.4  Input Capacitors
        5. 8.2.2.5  Inductor Selection
        6. 8.2.2.6  Output Capacitor Selection
        7. 8.2.2.7  Feedforward Capacitor
        8. 8.2.2.8  Bootstrap Capacitors
        9. 8.2.2.9  VCC Capacitors
        10. 8.2.2.10 BIAS Capacitors
        11. 8.2.2.11 Soft-Start Capacitors
        12. 8.2.2.12 Undervoltage Lockout Setpoint
        13. 8.2.2.13 PGOOD
        14. 8.2.2.14 Synchronization
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Layout Highlights
      2. 10.1.2 Compact Layout for EMI Reduction
      3. 10.1.3 Ground Plane and Thermal Considerations
      4. 10.1.4 Feedback Resistors
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
        1. 11.1.1.1 Custom Design With WEBENCH® Tools
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Support Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Support Resources
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7.3.5 Internal LDO, VCC UVLO, and Bias Input

The LM76005 has an internal LDO generating VCC voltage for control circuitry and MOSFET drivers. The nominal voltage for VCC is 3.29 V. The VCC pin must have a 1-µF to 4.7-µF bypass capacitor placed as close as possible to the pin and properly grounded. Do not load or short the VCC pin to ground during operation. Shorting the VCC pin to ground during operation can damage the device.

A UVLO prevents the LM76005 from operating until the VCC voltage exceeds VCC_UVLO. The VCC_UVLO threshold is 3.14 V and has approximately 565 mV of hysteresis, so the device operates until VCC drops below 2.575 V (typical). Hysteresis prevents the device from turning off during power up if VIN droops due to input current demands.

The LDO can generate VCC from two inputs: the supply voltage VIN and the BIAS input. The LDO power loss is calculated by ILDO × (VINLDO – VOUTLDO). The higher the difference between the input and output voltages of the LDO, the more losses occur to supply the same LDO output current. The BIAS input is designed to reduce the difference of the input and output voltages of the LDO to improve efficiency, especially at light load. TI recommends tying the BIAS pin to VOUT when the output voltage is equal to or greater than 3.3 V and less than 18 V. Tie the BIAS pin to ground for applications less than 3.3 V or greater than 18 V. BIAS can also tie to external voltage source if available to improve efficiency. When used, TI recommends a 1-µF to 10-µF high-quality ceramic capacitor be used to bypass the BIAS pin to ground. If there is high-frequency noise or voltage spikes present on VOUT (during transient events or fault conditions), TI recommends connecting a resistor (1 to 10 Ω) between VOUT and BIAS.

The VCC voltage is typically 3.29 V. When the LM76005 is operating in PFM mode with frequency foldback, VCC voltage is reduced to 3.1 V (typical) to further decrease the quiescent current and improve efficiency at very light loads.