SLUS223H April   1997  – October 2024 UC1842 , UC1843 , UC1844 , UC1845 , UC2842 , UC2843 , UC2844 , UC2845 , UC3842 , UC3843 , UC3844 , UC3845

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  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 Diagrams
    3. 7.3 Feature Description
      1. 7.3.1  Detailed Pin Description
        1. 7.3.1.1 COMP
        2. 7.3.1.2 VFB
        3. 7.3.1.3 ISENSE
        4. 7.3.1.4 RT/CT
        5. 7.3.1.5 GROUND
        6. 7.3.1.6 OUTPUT
        7. 7.3.1.7 VCC
        8. 7.3.1.8 VREF
      2. 7.3.2  Pulse-by-Pulse Current Limiting
      3. 7.3.3  Current-Sense
      4. 7.3.4  Error Amplifier With Low Output Resistance
      5. 7.3.5  Undervoltage Lockout
      6. 7.3.6  Oscillator
      7. 7.3.7  Synchronization
      8. 7.3.8  Shutdown Technique
      9. 7.3.9  Slope Compensation
      10. 7.3.10 Soft Start
      11. 7.3.11 Voltage Mode
    4. 7.4 Device Functional Modes
      1. 7.4.1 Normal Operation
      2. 7.4.2 UVLO Mode
  9. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Open-Loop Test Fixture
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  Input Bulk Capacitor and Minimum Bulk Voltage
        2. 8.2.2.2  Transformer Turns Ratio and Maximum Duty Cycle
        3. 8.2.2.3  Transformer Inductance and Peak Currents
        4. 8.2.2.4  Output Capacitor
        5. 8.2.2.5  Current Sensing Network
        6. 8.2.2.6  Gate Drive Resistor
        7. 8.2.2.7  VREF Capacitor
        8. 8.2.2.8  RT/CT
        9. 8.2.2.9  Start-Up Circuit
        10. 8.2.2.10 Voltage Feedback Compensation
          1. 8.2.2.10.1 Power Stage Poles and Zeroes
          2. 8.2.2.10.2 Slope Compensation
          3. 8.2.2.10.3 Open-Loop Gain
          4. 8.2.2.10.4 Compensation Loop
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
        1. 8.4.1.1 Feedback Traces
        2. 8.4.1.2 Bypass Capacitors
        3. 8.4.1.3 Compensation Components
        4. 8.4.1.4 Traces and Ground Planes
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Receiving Notification of Documentation Updates
    2. 9.2 Support Resources
    3. 9.3 Trademarks
    4. 9.4 Electrostatic Discharge Caution
    5. 9.5 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

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

8.2.3 Application Curves

UC1842 UC2842 UC3842 UC1843 UC2843 UC3843 UC1844 UC2844 UC3844 UC1845 UC2845 UC3845 Primary Side MOSFET Drain to Source Voltage at 240-V AC Input (100 V/div)Figure 8-7 Primary Side MOSFET Drain to Source Voltage at 240-V AC Input (100 V/div)
UC1842 UC2842 UC3842 UC1843 UC2843 UC3843 UC1844 UC2844 UC3844 UC1845 UC2845 UC3845 Output Voltage During 0.9-A to 2.7-A Load Transient (CH1: Output Voltage AC Coupled, 200 mV/div; CH4: Output Current, 1 A/div)Figure 8-9 Output Voltage During 0.9-A to 2.7-A Load Transient (CH1: Output Voltage AC Coupled, 200 mV/div; CH4: Output Current, 1 A/div)
UC1842 UC2842 UC3842 UC1843 UC2843 UC3843 UC1844 UC2844 UC3844 UC1845 UC2845 UC3845 Output Voltage Behavior at Full Load Start-Up (5 V/div)Figure 8-11 Output Voltage Behavior at Full Load Start-Up (5 V/div)
UC1842 UC2842 UC3842 UC1843 UC2843 UC3843 UC1844 UC2844 UC3844 UC1845 UC2845 UC3845 Primary Side MOSFET Drain to Source Voltage at 120-V AC Input (100 V/div)Figure 8-8 Primary Side MOSFET Drain to Source Voltage at 120-V AC Input (100 V/div)
UC1842 UC2842 UC3842 UC1843 UC2843 UC3843 UC1844 UC2844 UC3844 UC1845 UC2845 UC3845 Output Voltage Ripple at Full Load (100 mV/div)Figure 8-10 Output Voltage Ripple at Full Load (100 mV/div)