SLVSFF1C December   2021  – November 2025 LM5123-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Description (continued)
  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
    6. 6.6 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Device Enable/Disable (EN, VH Pin)
      2. 7.3.2  High Voltage VCC Regulator (BIAS, VCC Pin)
      3. 7.3.3  Light Load Switching Mode Selection (MODE Pin)
      4. 7.3.4  VOUT Range Selection (RANGE Pin)
      5. 7.3.5  Line Undervoltage Lockout (UVLO Pin)
      6. 7.3.6  Fast Restart Using VCC HOLD (VH Pin)
      7. 7.3.7  Adjustable Output Regulation Target (VOUT, TRK, VREF Pin)
      8. 7.3.8  Overvoltage Protection (VOUT Pin)
      9. 7.3.9  Power Good Indicator (PGOOD Pin)
      10. 7.3.10 Dynamically Programmable Switching Frequency (RT)
      11. 7.3.11 External Clock Synchronization (SYNC Pin)
      12. 7.3.12 Programmable Spread Spectrum (DITHER Pin)
      13. 7.3.13 Programmable Soft Start (SS Pin)
      14. 7.3.14 Wide Bandwidth Transconductance Error Amplifier and PWM (TRK, COMP Pin)
      15. 7.3.15 Current Sensing and Slope Compensation (CSP, CSN Pin)
      16. 7.3.16 Constant Peak Current Limit (CSP, CSN Pin)
      17. 7.3.17 Maximum Duty Cycle and Minimum Controllable On-Time Limits
      18. 7.3.18 Deep Sleep Mode and Bypass Operation (HO, CP Pin)
      19. 7.3.19 MOSFET Drivers, Integrated Boot Diode, and Hiccup Mode Fault Protection (LO, HO, HB Pin)
      20. 7.3.20 Thermal Shutdown Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 Device Status
        1. 7.4.1.1 Shutdown Mode
        2. 7.4.1.2 Configuration Mode
        3. 7.4.1.3 Active Mode
        4. 7.4.1.4 Sleep Mode
        5. 7.4.1.5 Deep Sleep Mode
      2. 7.4.2 Light Load Switching Mode
        1. 7.4.2.1 Forced PWM (FPWM) Mode
        2. 7.4.2.2 Diode Emulation (DE) Mode
        3. 7.4.2.3 Forced Diode Emulation Operation in FPWM Mode
        4. 7.4.2.4 Skip Mode
  9. 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 Application Ideas
      3. 8.2.3 Application Curves
    3. 8.3 System Example
  10. 9 Power Supply Recommendations
  11. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  12. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    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 Glossary
  13. 12Revision History
  14. 13Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • RGR|20
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.3.2 High Voltage VCC Regulator (BIAS, VCC Pin)

The device features a high voltage 5V VCC regulator, which is sourced from the BIAS pin. The internal VCC regulator turns on 50μs after the device is enabled and the 120μs device configuration starts when VCC is above the VCC UVLO threshold (VVCC-UVLO). The device configuration is reset when the device shuts down or VCC falls down below 2.2V. The preferred way to reconfigure the device is to shut down the device. During the configuration time, the light load switching mode and VOUT range are selected.

The high voltage VCC regulator allows the connection of the BIAS pin directly to supply voltages from 3.8V to 42V. When BIAS is less than the 5V VCC regulation target (VVCC-REG), the VCC output tracks the BIAS pin voltage with a small dropout voltage, which is caused by the 1.7Ω resistance of the VCC regulator.

The recommended VCC capacitor value is 4.7μF. The VCC capacitor should be populated between VCC and PGND as close to the device as possible. The recommended BIAS capacitor value is 1.0μF. The BIAS capacitor must be populated between BIAS and PGND close to the device.

LM5123-Q1 High Voltage VCC Regulator Figure 7-2 High Voltage VCC Regulator

The VCC regulator features a VCC current limit function that prevents device damage when the VCC pin is shorted to ground accidentally. The minimum sourcing capability of the VCC regulator is 100mA (IVCC-CL) during either the device configuration time or active mode operation. The minimum sourcing capability of the VCC regulator is reduced to 1mA during sleep mode or deep sleep mode, or when EN is less than VEN and VH is greater than VSYNC. The VCC regulator supplies the internal drivers and other internal circuits. The external MOSFETs must be carefully selected to make the driver current consumption less than IVCC-CL. The driver current consumption can be calculated in Equation 1.

Equation 1. IG = 2 × QG@5V × fSW

where

  • QG@5V is the N-channel MOSFET gate charge at 5V gate-source voltage.

If VIN operation below 3.8V is required, the BIAS pin must be connected to the output of the boost converter (VLOAD). By connecting the BIAS pin to VLOAD, the boost converter input voltage (VSUPPLY) can drop down to 0.8V if BIAS is greater than 3.8V. See Section 7.3.17 for more detailed information about the minimum VSUPPLY.