JAJSPY3 August   2023 LV5144

PRODUCTION DATA  

  1.   1
  2. 特長
  3. アプリケーション
  4. 概要
  5. Revision History
  6. 概要 (続き)
  7. Pin Configuration and Functions
    1. 6.1 Wettable Flanks
  8. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  9. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Input Range (VIN)
      2. 8.3.2  Output Voltage Setpoint and Accuracy (FB)
      3. 8.3.3  High-Voltage Bias Supply Regulator (VCC)
      4. 8.3.4  Precision Enable (EN/UVLO)
      5. 8.3.5  Power Good Monitor (PGOOD)
      6. 8.3.6  Switching Frequency (RT, SYNCIN)
        1. 8.3.6.1 Frequency Adjust
        2. 8.3.6.2 Clock Synchronization
      7. 8.3.7  Configurable Soft Start (SS/TRK)
        1. 8.3.7.1 Tracking
      8. 8.3.8  Voltage-Mode Control (COMP)
      9. 8.3.9  Gate Drivers (LO, HO)
      10. 8.3.10 Current Sensing and Overcurrent Protection (ILIM)
      11. 8.3.11 OCP Duty Cycle Limiter
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
      2. 8.4.2 Standby Mode
      3. 8.4.3 Active Mode
      4. 8.4.4 Diode Emulation Mode
      5. 8.4.5 Thermal Shutdown
  10. Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Design and Implementation
      2. 9.1.2 Power Train Components
        1. 9.1.2.1 Inductor
        2. 9.1.2.2 Output Capacitors
        3. 9.1.2.3 Input Capacitors
        4. 9.1.2.4 Power MOSFETs
      3. 9.1.3 Control Loop Compensation
      4. 9.1.4 EMI Filter Design
    2. 9.2 Typical Applications
      1. 9.2.1 Design 1 – 12-A High-Efficiency Synchronous Buck DC/DC Regulator
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
        3. 9.2.1.3 Application Curves
      2. 9.2.2 Design 2 – High Density, 12-V, 8-A Rail From 48-V Telecom Power
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
        3. 9.2.2.3 Application Curves
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
        1. 9.4.1.1 Power Stage Layout
        2. 9.4.1.2 Gate Drive Layout
        3. 9.4.1.3 PWM Controller Layout
        4. 9.4.1.4 Thermal Design and Layout
        5. 9.4.1.5 Ground Plane Design
      2. 9.4.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 サード・パーティ製品に関する免責事項
      2. 10.1.2 Development Support
    2. 10.2 Documentation Support
      1. 10.2.1 Related Documentation
        1. 10.2.1.1 PCB Layout Resources
        2. 10.2.1.2 Thermal Design Resources
    3. 10.3 ドキュメントの更新通知を受け取る方法
    4. 10.4 サポート・リソース
    5. 10.5 Trademarks
    6. 10.6 静電気放電に関する注意事項
    7. 10.7 用語集
  12. 11Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ(パッケージ|ピン)
サーマルパッド・メカニカル・データ
発注情報

Current Sensing and Overcurrent Protection (ILIM)

The LV5144 implements a lossless current sense scheme designed to limit the inductor current during an overload or short-circuit condition. Figure 8-8 portrays the popular current sense method using the on-state resistance of the low-side MOSFET. Meanwhile, Figure 8-9 shows an alternative implementation with current shunt resistor, RS. The LV5144 senses the inductor current during the PWM off-time (when LO is high).

GUID-C1AEFBB7-9E81-4A53-8842-CA7E6D26814C-low.svgFigure 8-8 MOSFET RDS(on) Current Sensing
GUID-3DBA5FBB-943E-48DB-BFD1-FB20551DE5F8-low.svgFigure 8-9 Shunt Resistor Current Sensing

The ILIM pin of the LV5144 sources a reference current that flows in an external resistor, designated RILIM, to program of the current limit threshold. A current limit comparator on the ILIM pin prevents further SW pulses if the ILIM pin voltage goes below GND. Figure 8-10 shows the implementation.

Resistor RILIM is tied to SW to use the RDS(on) of the low-side MOSFET as a sensing element (termed RDS(on) mode). Alternatively, RILIM is tied to a shunt resistor connected at the source of the low-side MOSFET (termed RSENSE mode). The LV5144 detects the appropriate mode at start-up and sets the source current amplitude and temperature coefficient (TC) accordingly.

The ILIM current with RDS-ON sensing is 200 µA at 27°C junction temperature and incorporates a TC of +4500 ppm/°C to generally track the RDS(on) temperature variation of the low-side MOSFET. Conversely, the ILIM current is a constant 100 µA in RSENSE mode. This controls the valley of the inductor current during a steady-state overload at the output. Depending on the chosen mode, select the resistance of RILIM using Equation 6.

Equation 6. GUID-BF2DB5C9-351B-4F57-911D-B98BC6F31745-low.gif

where

  • ΔIL is the peak-to-peak inductor ripple current
  • RDS(on)Q2 is the on-state resistance of the low-side MOSFET
  • IRDSON is the ILIM pin current in RDS-ON mode
  • RS is the resistance of the current-sensing shunt element
  • IRS is the ILIM pin current in RSENSE mode

Given the large voltage swings of ILIM in RDS(on) sensing mode, a capacitor designated CILIM connected from ILIM to PGND is essential to the operation of the valley current limit circuit. Choose this capacitance such that the time constant RILIM· CILIM is approximately 6 ns.

GUID-DB693DB1-8DED-450E-A4A9-B263EC56EF42-low.gifFigure 8-10 OCP Setpoint Defined by Current Source IRDSON and Resistor RILIM in RDS-ON Mode

Note that current sensing with a shunt component is typically implemented at lower output current levels to provide accurate overcurrent protection. Burdened by the unavoidable efficiency penalty, PCB layout, and additional cost implications, this configuration is not usually implemented in high-current applications (except where OCP setpoint accuracy and stability over the operating temperature range are critical specifications).