Application Note, V1.0, 6 September 2011 Application Note AN- EVAL-ICE2QR1765Z 20W5V Evaluation Board with QuasiResonant CoolSET® ICE2QR1765Z 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 © 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. 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. EVAL-ICE2QR1765Z-20W Title Revision History: Previous Version: Page 6 September 20111 none Subjects (major changes since last revision) 20W5V Evaluation Board with Quasi-Resonant CooLSET® ICE2QR1765Z License to Infineon Technologies Asia Pacific Pte Ltd V1.0 AN-PS0067 Winson Wong [email protected] Eric Kok [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 6 September 2011 EVAL-ICE2QR1765Z-20W Table of Contents 1 Content ............................................................................................................... 6 2 Evaluation Board ............................................................................................... 6 3 List of Features .................................................................................................. 6 4 Technical Specifications ................................................................................... 7 5 Circuit Description............................................................................................. 7 5.1 Mains Input and Rectification ...................................................................................................... 7 5.2 Integrated MOSFET and PWM Control........................................................................................ 7 5.3 Snubber Network .......................................................................................................................... 7 5.4 Output Stage .................................................................................................................................. 7 5.5 Feedback Loop .............................................................................................................................. 7 6 Circuit Operation ............................................................................................... 7 6.1 Startup Operation.......................................................................................................................... 7 6.2 Normal Mode Operation ............................................................................................................... 8 6.3 Primary side peak current control............................................................................................... 8 6.4 Digital Frequency Reduction ....................................................................................................... 8 6.5 Burst Mode Operation .................................................................................................................. 8 7 Protection Features ........................................................................................... 8 7.1 Vcc under voltage and over voltage protection......................................................................... 8 7.2 Foldback point protection ............................................................................................................ 9 7.3 Open loop/over load protection................................................................................................... 9 7.4 Adjustable output overvoltage protection.................................................................................. 9 7.5 Short winding protection.............................................................................................................. 9 7.6 Auto restart for over temperature protection ............................................................................. 9 8 Circuit diagram ................................................................................................ 10 8.1 PCB Top overlayer ...................................................................................................................... 11 8.2 PCB Bottom Layer ...................................................................................................................... 12 9 Component List ............................................................................................... 13 10 Transformer Construction .............................................................................. 14 11 Test Results ..................................................................................................... 15 11.1 Efficiency and standby performance ........................................................................................ 15 12 Waveform and scope plots ............................................................................. 16 12.1 Startup @85Vac and 12W load .................................................................................................. 16 12.2 Working at different zero crossing point .................................................................................. 17 12.3 Load transient response ............................................................................................................ 18 12.4 Burst mode operation ................................................................................................................. 18 13 References ....................................................................................................... 19 Application Note 5 6 September 2011 EVAL-ICE2QR1765Z-20W 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 ICE2QR1765Z Quasi-resonant CoolSET®.The target application of ICE2QR1765Z 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 ICE2QR1765Z 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 EVAL-ICE2QR1765Z-20W 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 6 September 2011 EVAL-ICE2QR1765Z-20W 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~265Vac 50Hz, 60Hz 5V 4.0A 20W >77% at full load <60mW@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 ICE2QR1765Z 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. ICE2QR1765Z also performs all necessary protection functions in flyback converters. Details about the information mentioned above are illustrated in the product datasheet. 5.3 Snubber Network A snubber network R1, C3 and D1 dissipate the energy of the leakage inductance and suppress ringing on the SMPS transformer. 5.4 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 capacitors 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. 5.5 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 ICE2QR1765Z, there is no need for external start up resistor, which can improve standby performance significantly. Application Note 7 6 September 2011 EVAL-ICE2QR1765Z-20W When VCC reaches the turn on voltage threshold 18V, the IC begins with a soft start. The soft-start implemented in ICE2QR1765Z 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 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 ICE2QR1765Z 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 ICE2QR1765Z 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: .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; .the up/down counter is 7; .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 Application Note 8 6 September 2011 EVAL-ICE2QR1765Z-20W 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 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 R5 and R5A 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 9 6 September 2011 EVAL-ICE2QR1765Z-20W 8 Circuit diagram 20W5V SMPS Demo board with ICE2QR1765Z V1.0 Figure 2 – Schematics Application Note 10 6 September 2011 EVAL-ICE2QR1765Z-20W 8.1 PCB Top overlayer Figure 3 –Component Legend – View from topside Application Note 11 6 September 2011 EVAL-ICE2QR1765Z-20W 8.2 PCB Bottom Layer Figure 4 Solder side copper – View from bottom side Application Note 12 6 September 2011 EVAL-ICE2QR1765Z-20W 9 Component List Items 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 Designator BR1 C7 C9 C8 C15 C14 C17 C10 C4 C5 C1 C6 C12 C11 C18 C3 D3 D2 D1 L3 L1 EMI F1 IC1 L2 IC2 R12 R10 R8 R3 R14 R15 R7 R6 R13 R5A R5 R5P R1 IC3 TR1 ZD1 Part Type 2KBB80R 0.1uF 1nF 100pF 1uF 1nF 0.1uF/50V 47pF/1kV 2.2nF/400V 2.2nF/250V,Y1 0.22u/275V 33uF/35V 220uF/25V 2200uF/25V 2200uF/25V 68uF/400V STP30L45 1N4148 UF4005 Choke 2x39mH, 0.9A 1.6A ICE2QR1765Z 1.5uH SFH617A‐3 22k 22k 6k8 200R 39k 6k82 1.2k 470R open 20R 1.5R 1.5R 150K/2W TL431 Transformer 22V Zener Diode Part No. Manufacturer Vishay Epcos Epcos Table 1– Component List Application Note 13 6 September 2011 EVAL-ICE2QR1765Z-20W 10 Transformer Construction Core and material: EF25/13/7, EPCOS N87 Bobbin: Vertical Version Primary Inductance, Lp=718μH, measured between pin 3 and pin 5 (Gapped to Inductance) Figure 5 – Transformer structure Figure 6 – Transformer complete – top view Start 3 Stop 4 No. of turns 26 Wire size 1XAWG#30 1 Layer /2 Primary 6 4 9 5 4 26 4XAWG#25 1XAWG#30 Secondary 1 /2 Primary 1 2 14 1XAWG#26 Auxiliary Table 2 wire gauge used of the transformer windings Application Note 14 6 September 2011 EVAL-ICE2QR1765Z-20W 11 11.1 Test Results Efficiency and standby performance Voltage (Vac) 85 85 85 85 115 115 115 115 150 150 150 150 180 180 180 180 230 230 230 230 265 265 265 265 Input Power (W) 6.113 12.517 19.09 25.873 6.052 12.256 18.275 24.851 6.04 12.126 18.14 24.376 5.97 12.021 18.041 24.149 6.149 12.01 17.97 23.95 6.285 12.203 17.81 23.69 Output Voltage (V) 5.002 4.996 4.99 4.984 5.002 4.996 4.99 4.984 5.002 4.996 4.99 4.984 5.002 4.996 4.99 4.984 5.002 4.996 4.99 4.984 5.002 4.996 4.99 4.984 Output Current (A) 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 Output Power (W) 5.002 9.992 14.97 19.936 5.002 9.992 14.97 19.936 5.002 9.992 14.97 19.936 5.002 9.992 14.97 19.936 5.002 9.992 14.97 19.936 5.002 9.992 14.97 19.936 Efficiency (%) 81.83 79.83 78.42 77.05 82.65 81.53 81.92 80.22 82.81 82.40 82.52 81.79 83.79 83.12 82.98 82.55 81.35 83.20 83.31 83.24 79.59 81.88 84.05 84.15 Table 3 – Efficiency vs. Load Application Note 15 6 September 2011 EVAL-ICE2QR1765Z-20W Figure 7 – Efficiency vs. Load Figure 8 Efficiency vs AC line voltage Figure 9 Standby Power at no load vs. AC line voltage 12 Waveform and scope plots All waveform and scope were recorded with LeCroy 44Xi oscilloscope. 12.1 Startup @85Vac and 12W load Application Note 16 6 September 2011 EVAL-ICE2QR1765Z-20W Figure 10 Constant charging VCC during startup Figure 11 Softstart of current in 4 steps Ch1 Drain source voltage Ch1 Drain source voltage Ch2 VCC supply voltage Ch2 VCC supply voltage Ch3 Zero crossing voltage Ch3 Zero crossing voltage Ch4 Current sense voltage Ch4 Current sense voltage Test condition: input 85Vac output 4A load Test condition: input 85Vac output 4A load 12.2 Working at different zero crossing point Figure 12 Working at first ZC point Figure 13 Working at 7th ZC point Ch1 Drain source voltage Ch1 Drain source voltage Ch2 VCC supply voltage Ch2 VCC supply voltage Ch3 Zero crossing voltage Ch3 Zero crossing voltage Ch4 Current sense voltage Ch4 Current sense voltage Test condition:5V/4A @85Vac Test condition:5V/0.5A @85Vac Application Note 17 6 September 2011 EVAL-ICE2QR1765Z-20W 12.3 Load transient response Figure 14 AC output ripple undershoot Figure 15 AC output ripple overshoot Ch1 Output ripple voltage div 100mv Ch1 Output ripple voltage div 110mv Ch4 Output current Ch4 Output current Measured with decouple capacitor 0.1uF+10uF, scope bandwidth 20MHz Measured with decouple capacitor 0.1uF+10uF, scope bandwidth 20MHz Test condition:0A to 4A Test condition:4A to 0A 12.4 Burst mode operation Figure 16 Entering burst mode Figure 17 Leaving burst mode Ch1 Drain source voltage Ch1 Drain source voltage Ch2 Supply voltage VCC Ch2 Supply voltage VCC Ch3 Feedback voltage Vfb Ch3 Feedback voltage Vfb Ch4 Current sense voltage Ch4 Current sense voltage Test condition: load jump from 4A to 0.2A at 85Vac line Test condition: load jump from 0.2A to 4A at 85Vac line Application Note 18 6 September 2011 EVAL-ICE2QR1765Z-20W Figure 18 AC output ripple during 85Vac Figure 21 AC output ripple during 265V Ch2 AC output ripple div 50mv Ch2 AC output ripple div 50mv Ch3 Feed back voltage Vfb Ch3 Feed back voltage Vfb Ch4 Current sense voltage Ch4 Current sense voltage Measured with decouple capacitor 0.1uF+10uF, scope bandwidth 20MHz Measured with decouple capacitor 0.1uF+10uF, scope bandwidth 20MHz Test condition : 85V ac line, 5V/0.1A Test condition : 264V ac line, 5V/0.1A 13 References [1] ICE2QR1765Z datasheet, Infineon Technologies AG, 2011 [2] ICE2QS03G Design Guide Infineon Technologies AG,2010 [3] Design Tips for flyback converters using the Quasi-Resonant (ANPS0005), Infineon Technologies AG, 2006 [4] Converter Design Using the Quasi-Resonant PWM Controller ICE2QS01 (ANPS0003), Infineon Technologies AG, 2006 [5] Determine the Switching Frequency of Quasi-Resonant Flyback Converters Designed with ICE2QS01 (ANPS0004), Infineon Technologies AG, 2006 Application Note 19 6 September 2011