SLUS223E April   1997  – January 2017 UC1842 , UC1843 , UC1844 , UC1845 , UC2842 , UC2843 , UC2844 , UC2845 , UC3842 , UC3843 , UC3844 , UC3845

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and Functions
  7. 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
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagrams
    3. 8.3 Feature Description
      1. 8.3.1  Detailed Pin Description
        1. 8.3.1.1 COMP
        2. 8.3.1.2 VFB
        3. 8.3.1.3 ISENSE
        4. 8.3.1.4 RT/CT
        5. 8.3.1.5 GROUND
        6. 8.3.1.6 OUTPUT
        7. 8.3.1.7 VCC
        8. 8.3.1.8 VREF
      2. 8.3.2  Pulse-by-Pulse Current Limiting
      3. 8.3.3  Current-Sense
      4. 8.3.4  Error Amplifier With Low Output Resistance
      5. 8.3.5  Undervoltage Lockout
      6. 8.3.6  Oscillator
      7. 8.3.7  Synchronization
      8. 8.3.8  Shutdown Technique
      9. 8.3.9  Slope Compensation
      10. 8.3.10 Soft Start
      11. 8.3.11 Voltage Mode
    4. 8.4 Device Functional Modes
      1. 8.4.1 Normal Operation
      2. 8.4.2 UVLO Mode
  9. Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Open-Loop Test Fixture
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1  Input Bulk Capacitor and Minimum Bulk Voltage
        2. 9.2.2.2  Transformer Turns Ratio and Maximum Duty Cycle
        3. 9.2.2.3  Transformer Inductance and Peak Currents
        4. 9.2.2.4  Output Capacitor
        5. 9.2.2.5  Current Sensing Network
        6. 9.2.2.6  Gate Drive Resistor
        7. 9.2.2.7  VREF Capacitor
        8. 9.2.2.8  RT/CT
        9. 9.2.2.9  Start-Up Circuit
        10. 9.2.2.10 Voltage Feedback Compensation
          1. 9.2.2.10.1 Power Stage Poles and Zeroes
          2. 9.2.2.10.2 Slope Compensation
          3. 9.2.2.10.3 Open-Loop Gain
          4. 9.2.2.10.4 Compensation Loop
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Feedback Traces
      2. 11.1.2 Bypass Capacitors
      3. 11.1.3 Compensation Components
      4. 11.1.4 Traces and Ground Planes
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Related Links
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

Features

  • Optimized for Off-Line and DC-to-DC Converters
  • Low Start-Up Current (< 1 mA)
  • Automatic Feedforward Compensation
  • Pulse-by-Pulse Current Limiting
  • Enhanced Load-Response Characteristics
  • Undervoltage Lockout With Hysteresis
  • Double-Pulse Suppression
  • High-Current Totem-Pole Output
  • Internally Trimmed Bandgap Reference
  • Up to 500-kHz Operation
  • Error Amplifier With Low Output Resistance

Applications

  • Switching Regulators of Any Polarity
  • Transformer-Coupled DC-DC Converters

Description

The UCx84x series of control integrated circuits provide the features that are necessary to implement off-line or DC-to-DC fixed-frequency current-mode control schemes, with a minimum number of external components. The internally implemented circuits include an undervoltage lockout (UVLO), featuring a start-up current of less than 1 mA, and a precision reference trimmed for accuracy at the error amplifier input. Other internal circuits include logic to ensure latched operation, a pulse-width modulation (PWM) comparator that also provides current-limit control, and a totem-pole output stage that is designed to source or sink high-peak current. The output stage, suitable for driving N-channel MOSFETs, is low when it is in the off state.

The UCx84x family offers a variety of package options, temperature range options, choice of maximum duty cycle, and choice of turnon and turnoff thresholds and hysteresis ranges. Devices with higher turnon or turnoff hysteresis are ideal choices for off-line power supplies, while the devices with a narrower hysteresis range are suited for DC-DC applications. The UC184x devices are specified for operation from –55°C to 125°C, the UC284x series is specified for operation from –40°C to 85°C, and the UC384x series is specified for operation from 0°C to 70°C.

Device Information(1)

PART NUMBER PACKAGE (PIN) BODY SIZE (NOM)
UC184x CDIP (8) 9.60 mm × 6.67 mm
LCCC (20) 8.89 mm × 8.89 mm
CFP (8) 9.21 mm × 5.97 mm
UC284x SOIC (8) 4.90 mm × 3.91 mm
SOIC (14) 8.65 mm × 3.91 mm
PDIP (8) 9.81 mm × 6.35 mm
UC384x SOIC (8) 4.90 mm × 3.91 mm
SOIC (14) 8.65 mm × 3.91 mm
PDIP (8) 9.81 mm × 6.35 mm
CFP (8) 9.21 mm × 5.97 mm
  1. For all available packages, see the orderable addendum at the end of the datasheet.

Simplified Application

UC1842 UC2842 UC3842 UC1843 UC2843 UC3843 UC1844 UC2844 UC3844 UC1845 UC2845 UC3845 simplified_app_slus223.gif