Application Note, V1.1, 12 November 2011 ® N e v e r s t o p t h i n k i n g . Published by Infineon Technologies AG 81726 Munich, Germany © 2011 Infineon Technologies AG All Rights Reserved. Legal Disclaimer The information given in this document shall in no event be regarded as a guarantee of conditions or characteristics. With respect to any examples or hints given herein, any typical values stated herein and/or any information regarding the application of the device, Infineon Technologies hereby disclaims any and all warranties and liabilities of any kind, including without limitation, warranties of non-infringement of intellectual property rights of any third party. Information For further information on technology, delivery terms and conditions and prices, please contact the nearest Infineon Technologies Office (www.infineon.com). Warnings Due to technical requirements, components may contain dangerous substances. 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EVAL-2QR0665Z-40W Title Revision History: 12 November 2011 Previous Version: 1.0 V1.1 Page Subjects (major changes since last revision) 12, 13 Revise typo in transformer information ® 40W20V Evaluation Board with Quasi-Resonant CooLSET ICE2QR0665Z License to Infineon Technologies Asia Pacific Pte Ltd AN-PS0062 Wong Siew Teng Winson [email protected] We Listen to Your Comments Any information within this document that you feel is wrong, unclear or missing at all? Your feedback will help us to continuously improve the quality of this document. Please send your proposal (including a reference to this document) to: [email protected] Application Note 4 12 November 2011 EVAL-2QR0665Z-40W Table of Contents 1 2 3 4 5 Content................................................................................................................ 6 Evaluation Board................................................................................................ 6 List of Features .................................................................................................. 6 Technical Specifications ................................................................................... 7 Circuit Description ............................................................................................. 7 5.1 5.2 5.3 5.4 Mains Input and Rectification .....................................................................................................7 Integrated MOSFET and PWM Control.......................................................................................7 Output Stage ................................................................................................................................7 Feedback Loop.............................................................................................................................7 6 Circuit Operation................................................................................................ 7 6.1 6.2 6.3 6.4 6.5 Startup Operation ........................................................................................................................7 Normal Mode Operation ..............................................................................................................8 Primary side peak current control..............................................................................................8 Digital Frequency Reduction ......................................................................................................8 Burst Mode Operation .................................................................................................................8 7 Protection Features ........................................................................................... 8 7.1 7.2 7.3 7.4 7.5 7.6 Vcc under voltage and over voltage protection ........................................................................8 Foldback point protection...........................................................................................................8 Open loop/over load protection..................................................................................................9 Adjustable output overvoltage protection.................................................................................9 Short winding protection ............................................................................................................9 Auto restart for over temperature protection ............................................................................9 8 Circuit diagram................................................................................................. 10 8.1 8.2 PCB Top overlayer.....................................................................................................................11 PCB Bottom Layer .....................................................................................................................11 9 10 11 Component Listmaybe .................................................................................... 12 Transformer Construction............................................................................... 13 Test Results...................................................................................................... 14 11.1 Efficiency and standby performance .......................................................................................14 12 References........................................................................................................ 15 Application Note 5 12 November 2011 EVAL-2QR0665Z-40W 1 Content This application note is a description of 40W switching mode power supply evaluation board designed in a ® quasi resonant flyback converter topology using ICE2QR0665Z Quasi-resonant CoolSET . The target application of ICE2QR0665Z are for set-top box, portable game controller, DVD player, netbook adapter and ® auxiliary power supply for LCD TV, etc. With the CoolMOS integrated in this IC, it greatly simplifies the design and layout of the PCB. Due to valley switching, the turn on voltage is reduced and this offers higher conversion efficiency comparing to hard-switching flyback converter. With the DCM mode control, the reverse recovery problem of secondary rectify diode is relieved. And for its natural frequency jittering with line voltage, the EMI performance is better. Infineon’s digital frequency reduction technology enables a quasi-resonant operation till very low load. As a result, the system efficiency, over the entire load range, is significantly improved compared to conventional free running quasi resonant converter implemented with only maximum switching frequency limitation at light load. In addition, numerous adjustable protection functions have been implemented in ICE2QR0665Z to protect the system and customize the IC for the chosen application. In case of failure modes, like open control-loop/over load, output overvoltage, and transformer short winding, the device switches into Auto Restart Mode or Latch-off Mode. By means of the cycle-by-cycle peak current limitation plus foldback point correction, the dimension of the transformer and current rating of the secondary diode can both be optimized. Thus, a cost effective solution can be easily achieved. 2 Evaluation Board Figure 1-EVALQR-40W-ICE2QR0665Z 3 List of Features ® 650V avalanche rugged CoolMOS with built in depletion startup cell Quasi-resonant operation Digital frequency reduction with decreasing load Cycle-by-cycle peak current limitation with foldback point correction Built-in digital soft-start Direct current sensing with internal Leading Edge Blanking Time VCC under voltage protection: IC stop operation, recover with softstart VCC over voltage protection: IC stop operation, recover with softstart Openloop/Overload protection: Auto Restart Output overvoltage protection: Latch-off with adjustable threshold Short-winding protection: Latch-off Over temperature protection: Autorestart Application Note 6 12 November 2011 EVAL-2QR0665Z-40W 4 Technical Specifications Input voltage Input frequency Output voltage and current Output power Average Efficiency Standby power Minimum switching frequency at full load, minimum input voltage 5 85Vac~265Vac 50Hz, 60Hz 20V 2.0A 40W >85% at full load <100mW@no load 65kHz Circuit Description 5.1 Mains Input and Rectification The AC line input side comprises the input fuse F1 as over current protection. The X2 Capacitors C1 and Choke L1 form a main filter to minimize the feedback of RFI into the main supply. After the bridge rectifier BR1, together with a smoothing capacitor C2, provide a voltage of 70VDC to 380 VDC depending on mains input voltage. 5.2 Integrated MOSFET and PWM Control ICE2QR0665Z is comprised of a power MOSFET and the quasi-resonant controller; this integrated solution greatly simplifies the circuit layout and reduces the cost of PCB manufacturing. The PWM switch-on is determined by the zero-crossing input signal and the value of the up/down counter. The PWM switch-off is determined by the feedback signal VFB and the current sensing signal VCS. ICE2QR0665Z also performs all necessary protection functions in flyback converters. Details about the information mentioned above are illustrated in the product datasheet. 5.3 Output Stage On the secondary side, 5V output, the power is coupled out via a schottky diode D21. The capacitors C21 provides energy buffering followed by the L-C filters L21 and C22 to reduce the output ripple and prevent interference between SMPS switching frequency and line frequency considerably. Storage capacitor C21 is designed to have an internal resistance (ESR) as small as possible. This is to minimize the output voltage ripple caused by the triangular current. 5.4 Feedback Loop For feedback, the output is sensed by the voltage divider of Rc1 and Rc3 and compared to TL431 internal reference voltage. Cc1, Cc2 and Rc4 comprise the compensation network. The output voltage of TL431 is converted to the current signal via optocoupler IC2 and two resistors Rc5 and Rc6 for regulation control. 6 Circuit Operation 6.1 Startup Operation Since there is a built-in startup cell in the ICE2QR0665Z, there is no need for external start up resistor, which can improve standby performance significantly. When VCC reaches the turn on voltage threshold 18V, the IC begins with a soft start. The soft-start implemented in ICE2QR0665Z is a digital time-based function. The preset soft-start time is 12ms with 4 steps. If not limited by other functions, the peak voltage on CS pin will increase step by step from 0.32V to 1V finally. After IC turns on, the Vcc voltage is supplied by auxiliary windings of the transformer. Application Note 7 12 November 2011 EVAL-2QR0665Z-40W 6.2 Normal Mode Operation The secondary output voltage is built up after startup. The secondary regulation control is adopted with TL431 and optocoupler. The compensation network Cc1, Cc2 and Rc4 constitute the external circuitry of the error amplifier of TL431. This circuitry allows the feedback to be precisely controlled with respect to dynamically varying load conditions, therefore providing stable control. 6.3 Primary side peak current control The MOSFET drain source current is sensed via external resistor R4 and R4A. Since ICE2QR0665Z is a current mode controller, it would have a cycle-by-cycle primary current and feedback voltage control which can make sure the maximum power of the converter is controlled in every switching cycle. 6.4 Digital Frequency Reduction During normal operation, the switching frequency for ICE2QR0665Z is digitally reduced with decreasing load. At light load, the MOSFET will be turned on not at the first minimum drain-source voltage time, but on the n th. The counter is in range of 1 to 7, which depends on feedback voltage in a time-base. The feedback voltage decreases when the output power requirement decreases, and vice versa. Therefore, the counter is set by monitoring voltage VFB. The counter will be increased with low VFB and decreased with high VFB. The thresholds are preset inside the IC. 6.5 Burst Mode Operation At light load condition, the SMPS enters into Active Burst Mode. At this stage, the controller is always active but the Vcc must be kept above the switch off threshold. During active burst mode, the efficiency increase significantly and at the same time it supports low ripple on Vout and fast response on load jump. For determination of entering Active Burst Mode operation, three conditions apply: 1. the feedback voltage is lower than the threshold of VFBEB(1.25V). Accordingly, the peak current sense voltage across the shunt resistor is 0.18; 2. the up/down counter is 7; 3. and a certain blanking time, 24ms (tBEB). Once all of these conditions are fulfilled, the Active Burst Mode flip-flop is set and the controller enters Active Burst Mode operation. This multi-condition determination for entering Active Burst Mode operation prevents mis-triggering of entering Active Burst Mode operation, so that the controller enters Active Burst Mode operation only when the output power is really low during the preset blanking time. During active burst mode, the maximum current sense voltage is reduced from 1V to 0.34V so as to reduce the conduction loss and the audible noise. At the burst mode, the FB voltage is changing like a sawtooth between 3.0 and 3.6V. The switching frequency is set to a fix frequency of 52kHz. The feedback voltage immediately increases if there is a high load jump. This is observed by one comparator. As the current limit is 34% during Active Burst Mode a certain load is needed so that feedback voltage can exceed VLB (4.5V). After leaving active burst mode, maximum current can now be provided to stabilize V O. In addition, the up/down counter will be set to 1 immediately after leaving Active Burst Mode. This is helpful to decrease the output voltage undershoot 7 Protection Features 7.1 Vcc under voltage and over voltage protection During normal operation, the VCC voltage is continuously monitored. When the Vcc voltage falls below the under voltage lock out level (VCCoff) or the Vcc voltage increases up to VCCovp, the IC will enter into auto restart mode. 7.2 Foldback point protection Application Note 8 12 November 2011 EVAL-2QR0665Z-40W For a quasi-resonant flyback converter, the maximum possible output power is increased when a constant current limit value is used for all the mains input voltage range. This is usually not desired as this will increase additional cost on transformer and output diode in case of output over power conditions. The internal fold back protection is implemented to adjust the VCS voltage limit according to the bus voltage. Here, the input line voltage is sensed using the current flowing out of ZC pin, during the MOSFET on-time. As the result, the maximum current limit will be lower at high input voltage and the maximum output power can be well limited versus the input voltage. 7.3 Open loop/over load protection In case of open control loop, feedback voltage is pulled up with internally block. After a fixed blanking time 30ms, the IC enters into auto restart mode. In case of secondary short-circuit or overload, regulation voltage VFB will also be pulled up, same protection is applied and IC will auto restart. 7.4 Adjustable output overvoltage protection During off-time of the power switch, the voltage at the zero-crossing pin ZC is monitored for output overvoltage detection. If the voltage is higher than the preset threshold 3.7V for a preset period 100μs, the IC is latched off. 7.5 Short winding protection The source current of the MOSFET is sensed via two shunt resistors R4 and R4A in parallel. If the voltage at the current sensing pin is higher than the preset threshold VCSSW of 1.68V during the on-time of the power switch, the IC is latched off. This constitutes a short winding protection. To avoid an accidental latch off, a spike blanking time of 190ns is integrated in the output of internal comparator. 7.6 Auto restart for over temperature protection The IC has a built-in over temperature protection function. When the controller’s temperature reaches 140 °C, the IC will shut down switch and enters into auto restart. This can protect power MOSFET from overheated. Application Note 9 12 November 2011 EVAL-2QR0665Z-40W 8 Circuit diagram 40W 20V SMPS Demoboard with ICE2QR0665Z Figure 2 – Schematics Application Note 10 12 November 2011 EVAL-2QR0665Z-40W 8.1 PCB Top overlayer Figure 3 –Component Legend – View from topside 8.2 PCB Bottom Layer Figure 4 Solder side copper – View from bottom side Application Note 11 12 November 2011 EVAL-2QR0665Z-40W 9 Component List Items Designator 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 BR1 NTC C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C14 C15 C16 D1 D2 D3 F1 FB1 IC1 IC2 IC3 J1~J7 L1 L2 R1 R3 R5 R5A R6 R7 R8 R10 R11 R12 R14 R15 TR1 ZD1 Part Type 1.5A/800V 2.5Ω S236 0.22μF/275Vac X2 0.1μF/275Vac X2 68μF/400V 2.2nF/400V 2.2nF/250V, Y1 33μF/35V 0.1μF 100pF 1nF 47pF/1000V 1000μF/25V 470μF/25V 100pF(0805) 100nF(0805) 1000μF/25V UF4005 1N4148 20A/150V 1.6A Fuse Ferrite Bead ICE2QR0665 SFH617A-3 TL431 Jumper 2X39mH,1.4A 1.5μH 150kΩ/2W 0Ω, (SMD 0805) 0.82Ω(0.5W, 1%) 0.82Ω(0.5W, 1%) 680Ω(SMD 0805) 1.2kΩ(SMD 0805) 22kΩ(SMD 0805) 43kΩ,0.1% (1206) 27kΩ,1%(1206) 10kΩ( 1%)(1206) 47kΩ 8.2kΩ 534μH 22V Part no. Manufacturer DF08M B57236S0259M000 B32922C3224K000 B32922C3104K000 B43501A9686M000 B32529C8222K000 DE1E3KX222MA4BL01 B41851A7336M000 RPER71H104K2K1A03B Vishay Epcos Epcos Epcos Epcos Epcos Murata Epcos Murata RPER71H102K2K1A03B Murata UF4005 Vishay MBR20H150CT Vishay Infineon B82734R2142B030 Epcos PC40EER28-Z TDK Table 1– Component List Application Note 12 12 November 2011 EVAL-2QR0665Z-40W 10 Transformer Construction Core and material: PC40EER28-Z Bobbin: Horizontal Version,BEER-28-1110CP Primary Inductance, Lp=534μH, measured between pin 5 and pin 4 (Gapped to Inductance) Air Gap in center leg Figure 5 – Transformer structure Figure 6 – Transformer complete – top view Table 2 wire gauge used of the transformer windings Application Note 13 12 November 2011 EVAL-2QR0665Z-40W 11 Test Results 11.1 Efficiency and standby performance Input Voltage (Vac) 90 90 90 90 100 100 100 100 230 230 230 230 Input Power (W) 11.32 22.61 34.35 46.12 11.28 22.48 34.07 45.62 11.44 22.24 33.37 44.26 Vo (V) 19.83 19.83 19.82 19.82 19.83 19.83 19.82 19.82 19.83 19.83 19.82 19.82 Io (A) 0.5081 1.0012 1.5093 2.0025 0.5081 1.0012 1.5093 2.0025 0.5081 1.0012 1.5093 2.0025 Po (W) 10.07562 19.8538 29.91433 39.68955 10.07562 19.8538 29.91433 39.68955 10.07562 19.8538 29.91433 39.68955 Efficiency (%) 89.01 87.81 87.09 86.06 89.32 88.32 87.80 87.00 88.07 89.27 89.64 89.67 Table 3 – Efficiency vs. Load Figure 7 – Efficiency vs. Output Load Application Note 14 12 November 2011 EVAL-2QR0665Z-40W Figure 8 Efficiency vs AC line voltage Figure 9 Standby input power vs AC line voltage 12 [1] [2] [3] [4] [5] References ICE2QR0665Z datasheet, Infineon Technologies AG, 2011 ICE2QS03G Design Guide Infineon Technologies AG,2010 Design Tips for flyback converters using the Quasi-Resonant (ANPS0005), Infineon Technologies AG, 2006 Converter Design Using the Quasi-Resonant PWM Controller ICE2QS01 (ANPS0003), Infineon Technologies AG, 2006 Determine the Switching Frequency of Quasi-Resonant Flyback Converters Designed with ICE2QS01 (ANPS0004), Infineon Technologies AG, 2006 Application Note 15 12 November 2011