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Power Supply Control Transitioning UC3854 Customers to the UCC3817 PFC Controller 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 Power Supply Control Products Power Supply Control Transitioning UC3854 Customers to the UCC3817 PFC Controller 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 Stage 1 Stage 2 VLINE 85-265 VAC + Vout - PFC Controller Power Supply Control Products PWM Controller Transitioning UC3854 Customers to the UCC3817 PFC Controller Power Supply Control 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 Power Supply Control Products Power Supply Control Transitioning UC3854 Customers to the UCC3817 PFC Controller 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 PFC BOOST CIRCUIT BUCK DERIVED CONVERTER ID1 L1 IQ2 D1 Gate Drive from Down Stream PWM IL L2 Q2 IAC Q1 CBULK IQ1 D2 Cout RLoad IC C1 Ct D2 UCC3817 Gate Drive Q2 Trailing Edge Modulation Ct Gate Drive Q1 Trailing Edge Modulation Ct D1 Ic with Trailing Edge/ Trailing Edge Modulation Rt Rt Gate Drive Q1 Leading Edge Modulation Ic with Leading Edge/ Trailing Edge Modulation Boost Capacitor Ripple Current Comparison Power Supply Control Products Synchronization Circuit Power Supply Control Transitioning UC3854 Customers to the UCC3817 PFC Controller 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 UC3854 CURRENT AMPLIFIER CONFIGURATION RSENSE RIN ZF + – CA PWM + RIN IMULTIPLIER PFC GATE DRIVE G CA = Zf +1 Zin Vnoise UCC3817 CURRENT AMPLIFIER CONFIGURATION RSENSE ZF + CA G CA = PWM + - RIN IMULTIPLIER RIN Vnoise Power Supply Control Products PFC GATE DRIVE Zf Zin Power Supply Control Transitioning UC3854 Customers to the UCC3817 PFC Controller 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 UC3854 External Circuitry that Creates the Feed Forward Voltage UC3854 + Iac ACin – VFF Rsense Circuitry that is Required to Configure UCC3817 Feed Forward Voltage UCC3817 Iac ACin – + VFF Rvff Rsense Power Supply Control Products Cvff Iac/2 Transitioning UC3854 Customers to the UCC3817 PFC Controller Power Supply Control Multiplier: •The Older UCC3854 Required a Bias Resistor From Vref to Iac For Proper Operation Bias Resistor Power Supply Control Products Power Supply Control Transitioning UC3854 Customers to the UCC3817 PFC Controller Multiplier: •The UCC3817’s Improved Multiplier Performance Improves System Operation Over a Wider Load Range •Performance Curves Can Be Found in the Data Sheet Multiplier Constant Power Performance Multiplier Output Current Imout vs. VAOUT 500 350 VAOUT = 5V 300 400 VAOUT = 4V VFF*IMO(uW) IMO(uA) 250 200 150 100 300 VAOUT = 3V 200 VAOUT = 2V 50 100 0 0 1 2 3 4 5 VAO(V) VO - Voltage Error Amplifier Output (VAOUT) - V Power Supply Control Products 0 1 2 3 4 Feed Forward Voltage - (VFF) - V 50 Transitioning UC3854 Customers to the UCC3817 PFC Controller Power Supply Control 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 Power Supply Control Products Transitioning UC3854 Customers to the UCC3817 PFC Controller Power Supply Control 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 Power Supply Control Products