SLUS161F April 1999 – May 2020 UCC2813-0 , UCC2813-1 , UCC2813-2 , UCC2813-3 , UCC2813-4 , UCC2813-5 , UCC3813-0 , UCC3813-1 , UCC3813-2 , UCC3813-3 , UCC3813-4 , UCC3813-5
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
8.3.1.8 VCC
VCC is the power input connection for this device. In normal operation, VCC is powered through a current limiting resistor to a low-impedance source. To prevent noise problems, bypass VCC to GND with a 0.1-µF ceramic capacitor in parallel as close to the VCC pin as possible. An electrolytic capacitor can also be used in addition to the ceramic capacitor.
Although quiescent VCC current is very low, total supply current is higher, depending on the OUT current. Total VCC current is the sum of quiescent VCC current and the average OUT current. Knowing the switching frequency f and the MOSFET gate charge (Qg), average OUT current can be calculated from Equation 3.
The UCCx813-x has a lower VCC (supply voltage) clamp of 13.5 V typical versus 30 V on the UC3842. For applications that require a higher VCC voltage, a resistor must be placed in series with VCC to increase the source impedance. The maximum value of this resistor is calculated with Equation 4.
where
- VIN(min) is the minimum voltage that is used to supply VCC
- VVCC(max) is the maximum VCC clamp voltage of the controller
- IVCC is the IC supply current without considering the gate driver current
- Qg is the external power MOSFET gate charge, and f is the switching frequency
Additionally, the UCCx813-x has an on-chip Zener diode to limit VCC to 13.5 V, which also limits the maximum OUT voltage. If the bias-supply source is always lower than 12 V, it may be connected directly to VCC. With UVLO thresholds at 4.1 V and 3.6 V for the UCCx813-3 and UCCx813-5, respectively, 5-V PWM operation is now possible.