ZHCSI53A May   2018  – November 2018 LM5122ZA

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
  3. 3 说明
    1.     Device Images
      1.      简化应用示意图
  4. 4 修订历史记录
  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 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  Undervoltage Lockout (UVLO)
      2. 7.3.2  High-Voltage VCC Regulator
      3. 7.3.3  Oscillator
      4. 7.3.4  Slope Compensation
      5. 7.3.5  Error Amplifier
      6. 7.3.6  PWM Comparator
      7. 7.3.7  Soft Start
      8. 7.3.8  HO and LO Drivers
      9. 7.3.9  Bypass Operation (VOUT = VIN)
      10. 7.3.10 Cycle-by-Cycle Current Limit
      11. 7.3.11 Clock Synchronization
      12. 7.3.12 Maximum Duty Cycle
      13. 7.3.13 Thermal Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 MODE Control (Forced-PWM Mode and Diode-Emulation Mode)
      2. 7.4.2 MODE Control (Skip-Cycle Mode and Pulse-Skipping Mode)
      3. 7.4.3 Hiccup-Mode Overload Protection
      4. 7.4.4 Slave Mode and SYNCOUT
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Feedback Compensation
      2. 8.1.2 Sub-Harmonic Oscillation
      3. 8.1.3 Interleaved Boost Configuration
      4. 8.1.4 DCR Sensing
      5. 8.1.5 Output Overvoltage Protection
      6. 8.1.6 SEPIC Converter Simplified Schematic
      7. 8.1.7 Non-Isolated Synchronous Flyback Converter Simplified Schematic
      8. 8.1.8 Negative to Positive Conversion
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  Timing Resistor RT
        2. 8.2.2.2  UVLO Divider RUV2, RUV1
        3. 8.2.2.3  Input Inductor LIN
        4. 8.2.2.4  Current Sense Resistor RS
        5. 8.2.2.5  Current Sense Filter RCSFP, RCSFN, CCS
        6. 8.2.2.6  Slope Compensation Resistor RSLOPE
        7. 8.2.2.7  Output Capacitor COUT
        8. 8.2.2.8  Input Capacitor CIN
        9. 8.2.2.9  VIN Filter RVIN, CVIN
        10. 8.2.2.10 Bootstrap Capacitor CBST and Boost Diode DBST
        11. 8.2.2.11 VCC Capacitor CVCC
        12. 8.2.2.12 Output Voltage Divider RFB1, RFB2
        13. 8.2.2.13 Soft-Start Capacitor CSS
        14. 8.2.2.14 Restart Capacitor CRES
        15. 8.2.2.15 Low-Side Power Switch QL
        16. 8.2.2.16 High-Side Power Switch QH and Additional Parallel Schottky Diode
        17. 8.2.2.17 Snubber Components
        18. 8.2.2.18 Loop Compensation Components CCOMP, RCOMP, CHF
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11器件和文档支持
    1. 11.1 接收文档更新通知
    2. 11.2 社区资源
    3. 11.3 商标
    4. 11.4 静电放电警告
    5. 11.5 术语表
  12. 12机械、封装和可订购信息

封装选项

机械数据 (封装 | 引脚)
散热焊盘机械数据 (封装 | 引脚)
订购信息

7.3.1 Undervoltage Lockout (UVLO)

The LM5122ZA features a dual level UVLO circuit. When the UVLO pin voltage is less than the 0.4-V UVLO standby enable threshold, the LM5122ZA is in the shutdown mode with all functions disabled. The shutdown comparator provides 0.1 V of hysteresis to avoid chatter during transition. If the UVLO pin voltage is greater than 0.4 V and below 1.2 V during power up, the controller is in standby mode with the VCC regulator operational and no switching at the HO and LO outputs. This feature allows the UVLO pin to be used as a remote shutdown function by pulling the UVLO pin down below the UVLO standby enable threshold with an external open collector or open drain device.

LM5122ZA UVLO-Remote-Standby.gifFigure 16. UVLO Remote Standby and Shutdown Control

If the UVLO pin voltage is above the 1.2-V UVLO threshold and VCC voltage exceeds the VCC UV threshold, a start-up sequence begins. UVLO hysteresis is accomplished with an internal 10-μA current source that is switched on or off into the impedance of the UVLO setpoint divider. When the UVLO pin voltage exceeds 1.2 V, the current source is enabled to quickly raise the voltage at the UVLO pin. When the UVLO pin voltage falls below the 1.2-V UVLO threshold, the current source is disabled causing the voltage at the UVLO pin to quickly fall. In addition to the UVLO hysteresis current source, a 5-μs deglitch filter on both rising and falling edge of UVLO toggling helps preventing chatter upon power up or down.

An external UVLO setpoint voltage divider from the supply voltage to AGND is used to set the minimum input operating voltage of the regulator. The divider must be designed such that the voltage at the UVLO pin is greater than 1.2 V when the input voltage is in the desired operating range. The maximum voltage rating of the UVLO pin is 15 V. If necessary, the UVLO pin can be clamped with an external zener diode. The UVLO pin should not be left floating. The values of RUV1 and RUV2 can be determined from Equation 1 and Equation 2.

Equation 1. LM5122ZA eq1_nvs954.gif
Equation 2. LM5122ZA eq2_nvs954.gif

where

  • VHYS is the desired UVLO hysteresis
  • VIN(STARTUP) is the desired startup voltage of the regulator during turn-on.

Typical shutdown voltage during turn-off can be calculated as follows:

Equation 3. LM5122ZA eq97_nvs954.gif