SGLS245E May 2020 – May 2020 UCC2813-0-Q1 , UCC2813-1-Q1 , UCC2813-2-Q1 , UCC2813-3-Q1 , UCC2813-4-Q1 , UCC2813-5-Q1
PRODUCTION DATA.
- 1 Features
- 2 Applications
- 3 Description
- 4 Revision History
- 5 Device Comparison Table
- 6 Pin Configuration and Functions
- 7 Specifications
-
8 Detailed Description
- 8.1 Overview
- 8.2 Functional Block Diagram
- 8.3
Feature Description
- 8.3.1 Detailed Pin Descriptions
- 8.3.2 Undervoltage Lockout (UVLO)
- 8.3.3 Self-Biasing, Active Low Output
- 8.3.4 Reference Voltage
- 8.3.5 Oscillator
- 8.3.6 Synchronization
- 8.3.7 PWM Generator
- 8.3.8 Minimum Off-Time Adjustment (Dead-Time Control)
- 8.3.9 Leading Edge Blanking
- 8.3.10 Minimum Pulse Width
- 8.3.11 Current Limiting
- 8.3.12 Overcurrent Protection and Full-Cycle Restart
- 8.3.13 Soft Start
- 8.3.14 Slope Compensation
- 8.4 Device Functional Modes
-
9 Application and Implementation
- 9.1 Application Information
- 9.2
Typical Application
- 9.2.1 Design Requirements
- 9.2.2
Detailed Design Procedure
- 9.2.2.1 Bulk Capacitor Calculation
- 9.2.2.2 Transformer Design
- 9.2.2.3 MOSFET and Output Diode Selection
- 9.2.2.4 Output Capacitor Calculation
- 9.2.2.5 Current Sensing Network
- 9.2.2.6 Gate Drive Resistor
- 9.2.2.7 REF Bypass Capacitor
- 9.2.2.8 RT and CT
- 9.2.2.9 Start-Up Circuit
- 9.2.2.10 Voltage Feedback Compensation Procedure
- 9.2.3 Application Curves
- 10Power Supply Recommendations
- 11Layout
- 12Device and Documentation Support
- 13Mechanical, Packaging, and Orderable Information
9.2.2.3 MOSFET and Output Diode Selection
The peak current of the MOSFET is calculated by Equation 10.
The MOSFET peak current is 1.425 A.
The RMS current of the MOSFET can be calculated as Equation 11.
where
- D is the MOSFET duty cycle at minimum bulk voltage and it can be calculated as Equation 12
The MOSFET RMS current is 0.75 A. With less than 0.9-Ω on-resistance, IRFB9N65A is selected as the primary-side MOSFET.
The diode peak current is the reflected MOSFET peak current on the secondary side.
The diode voltage stress is the output voltage plus the reflected input voltage. The voltage stress on the diode can be calculated by Equation 14.
Considering the ringing voltage spikes and voltage derating, the diode voltage rating must be higher than 50 V.
The diode average current is the output current (4 A), so 48CTQ060-1, with 60-V rating and 40-A average current capability, is selected.