Application Note, V1.0, 24 March 2011 A p p l i ca t i o n N o t e AN- EVAL-2QR4780Z-12W 12W5V Evaluation Board with QuasiResonant CoolSET® ICE2QR4780Z Power Management & Supply 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 © 2007 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. For information on the types in question, please contact the nearest Infineon Technologies Office. Infineon Technologies components may be used in life-support devices or systems only with the express written approval of Infineon Technologies, if a failure of such components can reasonably be expected to cause the failure of that life-support device or system or to affect the safety or effectiveness of that device or system. Life support devices or systems are intended to be implanted in the human body or to support and/or maintain and sustain and/or protect human life. If they fail, it is reasonable to assume that the health of the user or other persons may be endangered. Title Revision History: 24 March 2011 Previous Version: none Page V1.0 Subjects (major changes since last revision) ® 12W5V Evaluation Board with Quasi-Resonant CooLSET ICE2QR4780Z License to Infineon Technologies Asia Pacific Pte Ltd Wong Siew Teng Winson [email protected] Eric Kok [email protected] Jeoh Meng kiat [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] AN-PS0039 EVAL-2QR4780Z-12W Table of Contents 1 Content ............................................................................................................... 5 2 Evaluation Board ............................................................................................... 5 3 List of Features .................................................................................................. 5 4 Technical Specifications ................................................................................... 6 5 Circuit Description............................................................................................. 6 5.1 Mains Input and Rectification ...................................................................................................... 6 5.2 Integrated MOSFET and PWM Control........................................................................................ 6 5.3 Output Stage .................................................................................................................................. 6 5.4 Feedback Loop .............................................................................................................................. 6 6 Circuit Operation ............................................................................................... 6 6.1 Startup Operation.......................................................................................................................... 6 6.2 Normal Mode Operation ............................................................................................................... 6 6.3 Primary side peak current control............................................................................................... 7 6.4 Digital Frequency Reduction ....................................................................................................... 7 6.5 Burst Mode Operation .................................................................................................................. 7 7 Protection Features ........................................................................................... 7 7.1 Vcc under voltage and over voltage protection ......................................................................... 7 7.2 Foldback point protection ............................................................................................................ 7 7.3 Open loop/over load protection ................................................................................................... 8 7.4 Adjustable output overvoltage protection.................................................................................. 8 7.5 Short winding protection.............................................................................................................. 8 7.6 Auto restart for over temperature protection ............................................................................. 8 8 Circuit diagram .................................................................................................. 9 8.1 PCB Top overlayer ...................................................................................................................... 10 8.2 PCB Bottom Layer ...................................................................................................................... 11 9 Component List ............................................................................................... 12 10 Transformer Construction .............................................................................. 12 11 Test Results ..................................................................................................... 14 11.1 Efficiency and standby performance ........................................................................................ 14 12 Waveforms and Scope Plots........................................................................... 17 12.1 Startup at Full Load .................................................................................................................... 17 12.2 Zero Crossing Point During Normal Operation ....................................................................... 17 12.3 Load Transient Response .......................................................................................................... 18 12.4 Burst Mode Operation ................................................................................................................ 18 12.5 Protection Mode .......................................................................................................................... 19 13 References ....................................................................................................... 19 Application Note 4 24 March 2011 EVAL-2QR4780Z-12W 1 Content This application note is a description of 12W switching mode power supply evaluation board designed in a ® quasi resonant flyback converter topology using ICE2QR4780Z Quasi-resonant CoolSET .The target application of ICE2QR4780Z 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 ICE2QR4780Z 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-12W-ICE2QR4780Z 3 List of Features ® 800V 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 5 24 March 2011 EVAL-2QR4780Z-12W 4 Technical Specifications Input voltage Input frequency Output voltage and current Output power Efficiency Standby power Minimum switching frequency at full load, minimum input voltage 5 85Vac~282Vac 50Hz, 60Hz 5V 2.4A 12W >80% 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 overcurrent 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 ICE2QR4780Z 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. ICE2QR4780Z 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 ICE2QR4780Z, 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 ICE2QR4780Z is a digital time-based function. The preset soft-start time is 12ms with 4 steps. If not limited by other functions, the peak voltageon 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. 6.2 Normal Mode Operation Application Note 6 24 March 2011 EVAL-2QR4780Z-12W 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 ICE2QR4780Z 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 ICE2QR4780Z 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 nth. 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 (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 mistriggering 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 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 busrt mode, maximum current can now be provided to stabilize VO. 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 autorestart mode. 7.2 Foldback point protection Application Note 7 24 March 2011 EVAL-2QR4780Z-12W 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 autorestart. This can protect power MOSFET from overheated. Application Note 8 24 March 2011 EVAL-2QR4780Z-12W 8 Circuit diagram Figure 2 – Schematics Application Note 9 24 March 2011 EVAL-2QR4780Z-12W 8.1 PCB Top overlayer Figure 3 –Component Legend – View from topside Application Note 10 24 March 2011 EVAL-2QR4780Z-12W 8.2 PCB Bottom Layer Figure 4 Solder side copper – View from bottom side Application Note 11 24 March 2011 EVAL-2QR4780Z-12W 9 Component List Items 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 Designator BR1 F1 L21 R11 R13 R15 R16 R110 R111 R21 R22 R23 R24 R26 C11 C13 C14 C15 C16 C17 C18 C19 C21 C22 C23 C26 C27 L11 EMI TR1 IC12 IC21 D11 D12 ZD11 D21 IC11 Table 1– Component List 36 37 10 Part Type Part No. Bridge 800V 1.5A 1.0A/250Vac 1.5uH 330K, 2W 20R, SMD 0806 1.5R, 0.5W 20R, SMD 0806 8.2k, SMD 0806 33K 0.5W 68R, SMD 0806 1.1k, SMD 0806 1.0k, SMD 0806 10k 10k 0.22uF/305V 47uF/500V 2.2nF/400V 2.2nF/250V, Y1 33uF 0.1uF 47pF 1nF 1000uF/35V 1000uF/35V 220uF/25V 680nF 820pF,SMD 0806 2 x 27mH, 0.9A 1000uH (80:5:14) SFH617A-3 TL431 UF4006 1N485B 22V zener diode DF08M STPS30L45CT ICE2QR4780Z Manufacturer NEC B32922X2MKP/2H B43501A6476M000 MKPS5 2n2M630 DE1E3KX222MA4BL01 B41851A7336M Epcos Epcos Murata Epcos KZE KZE KZE B82732R2901B30 Epcos UF4006 Vishay ICE2QR4780Z Infineon Transformer Construction Core and material :EPCOS(N87), E20/10/6 Bobbin: Horizontal Version Primary Inductance, Lp=1000µH(±3%), measured between pin 4 and pin 5 (Gapped to Inductance) Air Gap in center leg Application Note 12 24 March 2011 EVAL-2QR4780Z-12W Figure 5 – Transformer structure Figure 6 – Transformer complete – top view Start 2 Stop 1 No. of turns 14 Wire size 1XAWG#30 Layer Auxiliary 3 7 4 6 40 5 1XAWG#30 3XAWG#27 /2 Primary Secondary 5 3 40 1XAWG#30 1 1 /2 Primary Table 2 wire gauge used of the transformer windings Application Note 13 24 March 2011 EVAL-2QR4780Z-12W 11 Test Results 11.1 Efficiency and standby performance Table 3 – Efficiency vs. Load Application Note 14 24 March 2011 EVAL-2QR4780Z-12W Efficiency vs Output Load 90.0000 88.0000 86.0000 Efficiency (%) 84.0000 82.7220 82.7368 82.4441 83.0153 82.0000 82.1556 80.0000 80.9329 82.5677 85Vac 282Vac 79.0534 78.0000 76.0000 74.0000 72.0000 70.0000 25 50 75 100 Load (%) Efficiency vs Output Load 90.0000 88.0000 86.0000 Efficiency (%) 84.0000 83.3742 84.1352 83.7612 83.8315 83.1309 82.0000 81.0244 83.2312 83.4911 115Vac 80.0000 230Vac 78.0000 76.0000 74.0000 72.0000 70.0000 25 50 75 100 Load (%) Figure 7a & 7b – Efficiency vs. Output Load Application Note 15 24 March 2011 EVAL-2QR4780Z-12W Efficiency vs AC Line Input Voltage 85.0000 84.2456 84.0084 84.0000 83.7636 83.6004 83.8315 Efficiency (%) 83.7247 83.0000 82.8945 83.1476 83.0153 82.2090 82.0000 Average Efficiency Full Load Efficiency 81.6980 81.0000 80.9329 80.0000 79.0000 85 115 150 180 230 282 AC Input Voltage (V) Figure 8 Efficiency vs AC line voltage Standby Power at No Load versus Input Voltage (AC) 1600 Output Power (mW) 1400 1200 1286 1297 1308 1340 1370 1284 1016 1014 1026 1041 1058 1085 657 658 666 671 681 705 290 292 298 310 322 17.8 18.32 19.08 19.95 23.35 85 115 150 180 230 1000 800 600 400 300 200 0 33.83 282 AC Input Voltage 0W 0.2W 0.5W 0.8w 1W Figure 9 Standby input power vs AC line voltage Application Note 16 24 March 2011 EVAL-2QR4780Z-12W 12 Waveforms and Scope Plots 12.1 Startup at Full Load Figure 10: Constant Charging VCC at Startup Figure 11: 4 Steps Softstart CH1 Supply Voltage, VCC CH1 Supply Voltage, VCC CH2 Zero Crossing Voltage, VZC CH2 Zero Crossing Voltage, VZC CH3 Current Sense Voltage, VCS CH3 Current Sense Voltage, VCS CH4 Feedback Voltage, VFB CH4 Feedback Voltage, VFB 12.2 Zero Crossing Point During Normal Operation st th Figure 12: Working at 1 ZC Figure 13: Working at 7 ZC CH1 Supply Voltage, VCC CH1 Supply Voltage, VCC CH2 Zero Crossing Voltage, VZC CH2 Zero Crossing Voltage, VZC CH3 Current Sense Voltage, VCS CH3 Current Sense Voltage, VCS CH4 Feedback Voltage, VFB CH4 Feedback Voltage, VFB Application Note 17 24 March 2011 EVAL-2QR4780Z-12W 12.3 Load Transient Response Figure 14: AC Output Ripple undershoot Figure 15: AC Output Ripple Overshoot CH1 Output Current, Io CH1 Output Current, Io CH4 Output Voltage, Vo CH4 Output Voltage, Vo 12.4 Burst Mode Operation Figure 16: Entering Burst Mode Figure 17: Leaving Burst Mode CH1 Feedback Voltage, VFB CH1 Feedback Voltage, VFB CH2 Zero Crossing Voltage, VZC CH2 Zero Crossing Voltage, VZC CH3 Current Sense Voltage, VCS CH3 Current Sense Voltage, VCS CH4 Output Voltage, Vo CH4 Output Voltage, Vo Condition: ZC=7, FB<1.2V, Blanking time =30ms Application Note 18 Condition: VFB>4.5V 24 March 2011 EVAL-2QR4780Z-12W 12.5 Protection Mode Figure 16: Over ZC Latch Figure 17: Over Load/ Open Loop Protection CH1 Feedback Voltage, VFB CH1 Feedback Voltage, VFB CH2 Zero Crossing Voltage, VZC CH2 Zero Crossing Voltage, VZC CH3 Current Sense Voltage, VCS CH3 Current Sense Voltage, VCS CH4 Supply Voltage, VCC CH4 Supply Voltage, VCC Condition: VZC > 3.7V 13 Condition: VFB > 4.5V for 30ms References [1] ICE2QR4780Z datasheet, Infineon Technologies AG, 2010 [2] Converter Design Using the Quasi-Resonant PWM Controller ICE2QS01, Infineon Technologies AG, 2006. [ANPS0003] [3] Design tips for flyback converters using the Quasi-Resonant PWM controller ICE2QS01, Infineon Technologies, 2006. [ANPS0005] [4] Determine the switching frequency of Quasi-Resonant flybacl converters designed with ICE2QS01, Infineon Technologies, 2006. [ANPS0004] [5] ICE2QRXX65/80X Quasi Resonance Coolset Design Guide. [ANPS0053] Application Note 19 24 March 2011