SNVSD08 February   2026 LM34938-Q1

ADVANCE INFORMATION  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 Handling Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
    7. 6.7 Typical Characteristics
  8. 7 Parameter Measurement Information
  9. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Buck-Boost Control Scheme
        1. 8.3.1.1 Buck Mode
        2. 8.3.1.2 Boost Mode
        3. 8.3.1.3 Buck-Boost Mode
      2. 8.3.2  Power Save Mode
      3. 8.3.3  Reference System
        1. 8.3.3.1 VIO LDO and nRST-PIN
      4. 8.3.4  Supply Voltage Selection – VSMART Switch and Selection Logic
      5. 8.3.5  Enable and Undervoltage Lockout
        1. 8.3.5.1 UVLO
      6. 8.3.6  Internal VCC Regulators
        1. 8.3.6.1 VCC1 Regulator
        2. 8.3.6.2 VCC2 Regulator
      7. 8.3.7  Error Amplifier and Control
        1. 8.3.7.1 Output Voltage Regulation
        2. 8.3.7.2 Output Voltage Feedback
        3. 8.3.7.3 Voltage Regulation Loop
        4. 8.3.7.4 Dynamic Voltage Scaling
      8. 8.3.8  Output Voltage Discharge
      9. 8.3.9  Peak Current Sensor
      10. 8.3.10 Short Circuit - Hiccup Protection
      11. 8.3.11 Current Monitor/Limiter
        1. 8.3.11.1 Overview
        2. 8.3.11.2 Output Current Limitation
        3. 8.3.11.3 Output Current Monitor
      12. 8.3.12 Oscillator Frequency Selection
      13. 8.3.13 Frequency Synchronization
      14. 8.3.14 Output Voltage Tracking
        1. 8.3.14.1 Analog Voltage Tracking
        2. 8.3.14.2 Digital Voltage Tracking
      15. 8.3.15 Slope Compensation
      16. 8.3.16 Configurable Soft Start
      17. 8.3.17 Drive Pin
      18. 8.3.18 Dual Random Spread Spectrum – DRSS
      19. 8.3.19 Gate Driver
      20. 8.3.20 Cable Drop Compensation (CDC)
      21. 8.3.21 CFG-pin and R2D Interface
      22. 8.3.22 Advanced Monitoring Features
        1. 8.3.22.1  Overview
        2. 8.3.22.2  BUSY
        3. 8.3.22.3  OFF
        4. 8.3.22.4  VOUT
        5. 8.3.22.5  IOUT
        6. 8.3.22.6  INPUT
        7. 8.3.22.7  TEMPERATURE
        8. 8.3.22.8  CML
        9. 8.3.22.9  OTHER
        10. 8.3.22.10 ILIM_OP
        11. 8.3.22.11 nFLT/nINT Pin Output
        12. 8.3.22.12 Status Byte
      23. 8.3.23 Protection Features
        1. 8.3.23.1  Thermal Shutdown (TSD)
        2. 8.3.23.2  Over Current Protection
        3. 8.3.23.3  Output Overvoltage Protection 1 (OVP1)
        4. 8.3.23.4  Output Overvoltage Protection 2 (OVP2)
        5. 8.3.23.5  Input Voltage Protection (IVP)
        6. 8.3.23.6  Input Voltage Regulation (IVR)
        7. 8.3.23.7  Power Good
        8. 8.3.23.8  Boot-Strap Undervoltage Protection
        9. 8.3.23.9  Boot-strap Overvoltage Clamp
        10. 8.3.23.10 CRC - CHECK
    4. 8.4 Device Functional Modes
      1. 8.4.1 Overview
      2. 8.4.2 Logic State Description
    5. 8.5 Programming
      1. 8.5.1 I2C Bus Operation
      2. 8.5.2 Clock Stretching
      3. 8.5.3 Data Transfer Formats
      4. 8.5.4 Single READ From a Defined Register Address
      5. 8.5.5 Sequential READ Starting from a Defined Register Address
      6. 8.5.6 Single WRITE to a Defined Register Address
      7. 8.5.7 Sequential WRITE Starting at a Defined Register Address
  10. 9 LM34938-Q1 Registers
  11. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1  Custom Design With WEBENCH® Tools
        2. 10.2.2.2  Frequency
        3. 10.2.2.3  Feedback Divider
        4. 10.2.2.4  Inductor and Current Sense Resistor Selection
        5. 10.2.2.5  Output Capacitor
        6. 10.2.2.6  Input Capacitor
        7. 10.2.2.7  Slope Compensation
        8. 10.2.2.8  UVLO Divider
        9. 10.2.2.9  Soft-Start Capacitor
        10. 10.2.2.10 MOSFETs QH1 and QL1
        11. 10.2.2.11 MOSFETs QH2 and QL2
        12. 10.2.2.12 Loop Compensation
        13. 10.2.2.13 External Component Selection
      3. 10.2.3 Application Curves
    3. 10.3 Power Supply Recommendations
    4. 10.4 Layout
      1. 10.4.1 Layout Guidelines
        1. 10.4.1.1 Power Stage Layout
        2. 10.4.1.2 Gate Driver Layout
        3. 10.4.1.3 Controller Layout
      2. 10.4.2 Layout Example
    5. 10.5 Wireless Charging Supply
    6. 10.6 USB-PD Source with Power Path
    7. 10.7 Parallel (Multiphase) Operation
  12. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    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

8.3.6.1 VCC1 Regulator

The LM34938-Q1 features a VCC1 regulator which provides an LDO output for auxiliary use in the system. VCC1 gets directly supplied by VIN pin. In most applications the output is used to supply the I2C controller device which sends data to the LM34938-Q1. See the application below.


LM34938-Q1 Simplified Schematic

Figure 8-12 Simplified Schematic

The VCC1 starts up when the device enters the standby mode to allow the power sequence of the system to be met. See a typical power up sequence below.


LM34938-Q1 Timing Diagram VCC Regulator

Figure 8-13 Timing Diagram VCC Regulator

The VCC1 regulator provides high DC accuracy at light load condition to support a use as a reference voltage for external circuits for example a comparator or operational amplifier.

The VCC1 is enabled/disabled via R2D or the I2C interface . Therefore the start-up of VCC1 is gated by the R2D readout.