SNVSBJ3A April   2020  – September 2020 LM25183

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 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  Integrated Power MOSFET
      2. 7.3.2  PSR Flyback Modes of Operation
      3. 7.3.3  Setting the Output Voltage
        1. 7.3.3.1 Diode Thermal Compensation
      4. 7.3.4  Control Loop Error Amplifier
      5. 7.3.5  Precision Enable
      6. 7.3.6  Configurable Soft Start
      7. 7.3.7  External Bias Supply
      8. 7.3.8  Minimum On-Time and Off-Time
      9. 7.3.9  Overcurrent Protection
      10. 7.3.10 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
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Design 1: Wide VIN, Low IQ PSR Flyback Converter Rated at 12 V, 0.6 A
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1  Custom Design With WEBENCH® Tools
          2. 8.2.1.2.2  Custom Design With Excel Quickstart Tool
          3. 8.2.1.2.3  Flyback Transformer – T1
          4. 8.2.1.2.4  Flyback Diode – DFLY
          5. 8.2.1.2.5  Leakgae Inductance Clamp Circuit – DF, DCLAMP
          6. 8.2.1.2.6  Output Capacitor – COUT
          7. 8.2.1.2.7  Input Capacitor – CIN
          8. 8.2.1.2.8  Feedback Resistor – RFB
          9. 8.2.1.2.9  Thermal Compensation Resistor – RTC
          10. 8.2.1.2.10 UVLO Resistors – RUV1, RUV2
          11. 8.2.1.2.11 Soft-Start Capacitor – CSS
          12.        50
      2. 8.2.2 Application Curves
      3. 8.2.3 Design 2: PSR Flyback Converter With Dual Outputs of 15 V and –15 V at 0.3 A
        1. 8.2.3.1 Design Requirements
        2. 8.2.3.2 Detailed Design Procedure
          1. 8.2.3.2.1 Flyback Transformer – T1
          2. 8.2.3.2.2 Flyback Diodes – DFLY1 and DFLY2
          3. 8.2.3.2.3 Input Capacitor – CIN
          4. 8.2.3.2.4 Output Capacitors – COUT1, COUT2
          5. 8.2.3.2.5 Feedback Resistor – RFB
          6. 8.2.3.2.6 Thermal Compensation Resistor – RTC
          7. 8.2.3.2.7 Output Voltage Clamp Zeners – DOUT1 and DOUT2
        3. 8.2.3.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Examples
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
      2. 11.1.2 Development Support
        1. 11.1.2.1 Custom Design With WEBENCH® Tools
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Support Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7.3.5 Precision Enable

The precision EN/UVLO input supports adjustable input undervoltage lockout (UVLO) with hysteresis for application-specific power-up and power-down requirements. EN/UVLO connects to a comparator with a 1.5-V reference voltage and 50-mV hysteresis. An external logic signal can be used to drive the EN/UVLO input to toggle the output on and off for system sequencing or protection. The simplest way to enable the LM25183 is to connect EN/UVLO directly to VIN. This allows the LM25183 to start up when VIN is within its valid operating range. However, many applications benefit from using resistor divider RUV1 and RUV2 as shown in Figure 7-3 to establish a precision UVLO level.

GUID-6FFE038C-C260-4133-912F-6445CCCE6833-low.gif Figure 7-3 Programmable Input Voltage UVLO With Hysteresis

Use Equation 10 and Equation 11 to calculate the input UVLO voltages turnon and turnoff voltages, respectively.

Equation 10. GUID-797FB31F-AE01-45E7-A396-ECF707C927E0-low.gif
Equation 11. GUID-9EB680FB-F391-4472-857A-B199150A2194-low.gif

where

  • VUV-RISING and VUV-FALLING are the UVLO comparator thresholds
  • IUV-HYST is the hysteresis current

The LM25183 also provides a low-IQ shutdown mode when the EN/UVLO voltage is pulled below a base-emitter voltage drop (approximately 0.6 V at room temperature). If the EN/UVLO voltage is below this hard shutdown threshold, the internal LDO regulator powers off, and the internal bias-supply rail collapses, shutting down the bias currents of the LM25183. The LM25183 operates in standby mode when the EN/UVLO voltage is between the hard shutdown and precision-enable thresholds.