1. Review the Similarities and Differences of Both Controllers
Objective:
Review the Similarities and Differences of Both Controllers
Highlight the Application Differences That Transitioning
Customers Need to Know About
Rectified Input Voltage
Input Current

2. Typical Two Stage Power Converter With PFC Front End
Similarities:
Designed to Control PFC Power Stage
Average Current Mode Control
Achieved Near Unity Power Factor by Shaping the Input Current Waveform
These Controllers Are Typically Designed in Two-stage Systems
Typical Two Stage Power Converter With PFC Front End

3. Differences: PWM Modulation
UC3854 Uses Traditional Trailing Edge PWM Modulation
UCC3817 Uses Leading Edge Modulation
Current Amplifier
UC3854 Is Set up in a Non Inverting Configuration
UCC3817 Is Set up in an Inverting Configuration
Voltage Feed Forward(VFF)
UC3854 Generates VFF From the Input and Requires a Two Pole Filter
UCC3817 Generates VFF Internally From the Iac Current and Only
Requires a Single Pole Filter
Multiplier
The Older UC3854 Required a Bias Resistor From the Internal Reference
to the Iac Pin for Proper Operation
The UCC3817 Multiplier Has Better Overall Parametric Performance

4. Boost Capacitor Ripple Current Comparison Synchronization Circuit
PWM Modulation
UC3854 Uses Traditional Trailing Edge PWM Modulation
UCC3817 Uses Leading Edge PWM Modulation
When Properly Synchronized With a Down Stream Converter Can
Have up to 40% Less RMS Current Through the Boost Capacitor
Boost Capacitor Ripple Current Comparison
Synchronization Circuit

5. Noise Rejection Than the Non Inverting Configuration
Current Amplifier Configuration
UC3854 Uses a Non Inverting Amplifier Configuration
UCC3817 Uses a Inverting Amplifier Configuration That Can Have Better
Noise Rejection Than the Non Inverting Configuration

6. Voltage Feed Forward(VFF)
UC3854 Generates VFF From a Voltage Divider That Requires a Two Pole Filter
5 Components Required to Generate the VFF
UCC3817 Generates the VFF From an Internal Current Source That Requires a
Single Pole Filter
2 Components Required to Generate the VFF

7. Multiplier:
The Older UCC3854 Required a Bias Resistor From Vref to Iac For Proper Operation
Bias Resistor

8. Multiplier:
The UCC3817’s Improved Multiplier Performance Improves System
Operation Over a Wider Load Range
Performance Curves Can Be Found in the Data Sheet

9. Recap Reasons For Transitioning From The UC3854 to The UCC3817
The UCC3817 Has Better Noise Immunity Because of the Current Amplifier
Configuration
It Takes Fewer Components to Use the UCC3817 in the Application
Leading Edge Modulation When Synchronized Correctly Will Reduce the RMS
Current in the Boost Capacitor
Improved Multiplier Performance Allows the System to Operate With a Wider Load Range

10. UCC3817 EVM Availability
EVMs Are Available Presently but in Limited Quantities
Contact Judy Pacheco
EVMs Are Presently Being Put Into the TI System and Will Be Available in August