SLUS270H March   1999  – April 2025 UCC1801 , UCC1802 , UCC1803 , UCC1804 , UCC1805 , UCC2800 , UCC2801 , UCC2802 , UCC2803 , UCC2804 , UCC2805 , UCC3800 , UCC3801 , UCC3802 , UCC3803 , UCC3804 , UCC3805

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison
  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 Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Detailed Pin Description
        1. 7.3.1.1 COMP
        2. 7.3.1.2 FB
        3. 7.3.1.3 CS
        4. 7.3.1.4 RC
        5. 7.3.1.5 GND
        6. 7.3.1.6 OUT
        7. 7.3.1.7 VCC
        8. 7.3.1.8 Pin 8 (REF)
      2. 7.3.2  Undervoltage Lockout (UVLO)
      3. 7.3.3  Self-Biasing, Active Low Output
      4. 7.3.4  Reference Voltage
      5. 7.3.5  Oscillator
      6. 7.3.6  Synchronization
      7. 7.3.7  PWM Generator
      8. 7.3.8  Minimum Off-Time Setting (Dead-Time Control)
      9. 7.3.9  Leading Edge Blanking
      10. 7.3.10 Minimum Pulse Width
      11. 7.3.11 Current Limiting
      12. 7.3.12 Overcurrent Protection and Full Cycle Restart
      13. 7.3.13 Soft Start
      14. 7.3.14 Slope Compensation
    4. 7.4 Device Functional Modes
      1. 7.4.1 Normal Operation
      2. 7.4.2 UVLO Mode
      3. 7.4.3 Soft Start Mode
      4. 7.4.4 Fault Mode
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Current Sensing Network
        2. 8.2.2.2 Gate Drive Resistor
        3. 8.2.2.3 Vref Capacitor
        4. 8.2.2.4 RTCT
        5. 8.2.2.5 Start-Up Circuit
        6. 8.2.2.6 Voltage Feedback Compensation
          1. 8.2.2.6.1 Power Stage Gain, Zeroes, and Poles
          2. 8.2.2.6.2 Compensation Loop
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Related Links
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

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

7.3.11 Current Limiting

A 1-V (typical) cycle-by-cycle current limit threshold is incorporated into the UCC280x family. Note that the 100-ns leading edge blanking pulse is applied to this current limiting circuitry. The blanking overrides the current limit comparator output to prevent the leading edge switch noise from triggering a current limit function. Propagation delay from the current limit comparator to the output is typically 70 ns. This high-speed path minimizes power semiconductor dissipation during an overload by abbreviating the ON time.

For increased efficiency in the current sense circuitry, the circuit shown in Figure 7-16 can be used. Resistors RA and RB bias the actual current sense resistor voltage up, allowing a small current sense amplitude to be used. This circuitry provides current limiting protection with lower power loss current sensing.

UCC1801 UCC1802 UCC1803 UCC1804 UCC1805 UCC2800 UCC2801 UCC2802 UCC2803 UCC2804 UCC2805 UCC3800 UCC3801 UCC3802 UCC3803 UCC3804 UCC3805 Biasing CS For Lower Current Sense VoltageFigure 7-16 Biasing CS For Lower Current Sense Voltage
UCC1801 UCC1802 UCC1803 UCC1804 UCC1805 UCC2800 UCC2801 UCC2802 UCC2803 UCC2804 UCC2805 UCC3800 UCC3801 UCC3802 UCC3803 UCC3804 UCC3805 CS Pin Voltage with BiasingFigure 7-17 CS Pin Voltage with Biasing

The example shown uses a 200-mV full scale signal at the current sense resistor. Resistor RB biases this up by approximately 700 mV to mate with the 0.9-V minimum specification of the current limit comparator of the IC. The value of resistor RA changes with the specific IC used, due to the different reference voltages. The resistor values must be selected for minimal power loss. For example, a 50-µA bias sets RB = 13 kΩ, RA = 75 kΩ (UCCx800, UCC2801, UCC2802, and UCC2804), or RA = 56 kΩ with the UCC2803 and UCC2805 devices.