SLUSC14A May   2015  – February 2019 UC1845A-SP

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
      2.      VREF Radiation Drift Curve
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 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. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 UVLO
      2. 8.3.2 Reference
      3. 8.3.3 Totem-Pole Output
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Oscillator
        2. 9.2.2.2 Current Sensing and Limiting
        3. 9.2.2.3 Error Amplifier
      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 Input/Output 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 Receiving Notification of Documentation Updates
    2. 12.2 Community Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • FK|20
  • HKU|10
  • JG|8
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9.2.2.1 Oscillator

The UC1845A-SP oscillator is programmed as shown in Figure 13. Timing capacitor CT is charged from VREF (5 V) through the timing resistor RT, and discharged by an internal current source. The first step in selecting the oscillator components is to determine the required circuit dead time. Once obtained, Figure 14 is used to pinpoint the nearest standard value of CT for a given dead time. Next, the appropriate RT value is interpolated using the parameters for CT and oscillator frequency. Figure 15 shows the RT/CT combinations versus oscillator frequency. The timing resistor can be calculated from the following formula.

Equation 1. UC1845A-SP eqn1_slusci6.gif
UC1845A-SP sch_EA_comp_LUSC14.gifFigure 12. E/A Compensation Circuit for Continuous Boost and Flyback Topologies

The UC1845A-SP has an internal divide-by-two flip-flop driven by the oscillator for a 50% maximum duty cycle. Therefore, their oscillators must be set to run at twice the desired power supply switching frequency.

UC1845A-SP oscillator_LUSC14.gifFigure 13. Oscillator Programming
UC1845A-SP gr_dt_vs_Ct_lusc14.gifFigure 14. Dead Time vs CT (RT > 5 kΩ)
UC1845A-SP gr_RT_freq_lusc14.gifFigure 15. Timing Resistance vs Frequency