FSQ0465RS

FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation December 2009 FSQ0465RS/RB Green-Mode Fairchild Power Switch (FPS™) for Quasi-Resonant Operation - Low EMI and High Efficiency Features ! Optimized for Quasi-Resonant Converters (QRC) ! Low EMI through Variable Frequency Control and AVS Description A Quasi-Resonant Converter (QRC) generally shows lower EMI and higher power conversion efficiency than a conventional hard-switched converter with a fixed switching frequency. The FSQ-series is an integrated Pulse-Width Modulation (PWM) controller and SenseFET specifically designed for quasi-resonant operation and Alternating Valley Switching (AVS). The PWM controller includes an integrated fixed-frequency oscillator, Under-Voltage Lockout (UVLO), LeadingEdge Blanking (LEB), optimized gate driver, internal softstart, temperature-compensated precise current sources for a loop compensation, and self-protection circuitry. Compared with a discrete MOSFET and PWM controller solution, the FSQ-series can reduce total cost, component count, size, and weight; while simultaneously increasing efficiency, productivity, and system reliability. This device provides a basic platform for cost-effective designs of quasi-resonant switching flyback converters. (Alternating Valley Switching) ! High-Efficiency through Minimum Voltage Switching ! Narrow Frequency Variation Range over Wide Load and Input Voltage Variation Power Consumption ! Advanced Burst-Mode Operation for Low Standby ! Simple Scheme for Sync Voltage Detection ! Pulse-by-Pulse Current Limit ! Various Protection Functions: Overload Protection ! ! ! ! (OLP), Over-Voltage Protection (OVP), Abnormal Over-Current Protection (AOCP), Internal Thermal Shutdown (TSD) with Hysteresis, Output Short Protection (OSP) Under-Voltage Lockout (UVLO) with Hysteresis Internal Startup Circuit Internal High-Voltage Sense FET (650V) Built-in Soft-Start (17.5ms) Applications ! Power Supply for LCD TV and Monitor, VCR, SVR, STB, and DVD & DVD Recorder ! Adapter Related Resources Visit: http://www.fairchildsemi.com/apnotes/ for: ! AN-4134: Design Guidelines for Offline Forward ! ! ! ! ! ! ! Converters Using Fairchild Power Switch (FPS™) AN-4137: Design Guidelines for Offline Flyback Converters Using Fairchild Power Switch (FPS™) AN-4140: Transformer Design Consideration for Offline Flyback Converters Using Fairchild Power Switch (FPS™) AN-4141: Troubleshooting and Design Tips for Fairchild Power Switch (FPS™) Flyback Applications AN-4145: Electromagnetic Compatibility for Power Converters AN-4147: Design Guidelines for RCD Snubber of Flyback Converters AN-4148: Audible Noise Reduction Techniques for Fairchild Power Switch (FPS™) Applications AN-4150: Design Guidelines for Flyback Converters Using FSQ-Series Fairchild Power Switch (FPS™) © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation Ordering Information Maximum Output Power(1) Product Number FSQ0465RSWDTU FSQ0465RBWDTU FSQ0465RSLDTU PKG.(5) Operating Current RDS(ON) Temp. Limit Max. 1.8A 3.0A 1.8A 2.6Ω 230VAC±15%(2) Adapter(3) 85-265VAC Open Open Adapter(3) Frame(4) Frame(4) Replaces Devices TO-220F TO220F(L- -25 to +85°C Forming) TO220F(LForming) FSCM0465R FSDM0465RE 60W 70W 33W 48W FSCM0465R FSDM0465RE FSQ0465RBLDTU 3.0A For Fairchild’s definition of Eco Status, please visit: http://www.fairchildsemi.com/company/green/rohs_green.html. Notes: 1. The junction temperature can limit the maximum output power. 2. 230VAC or 100/115VAC with doubler. 3. Typical continuous power in a non-ventilated enclosed adapter measured at 50°C ambient temperature. 4. Maximum practical continuous power in an open-frame design at 50°C ambient. 5. Eco Status, RoHS. © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 2 www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation Application Diagram VO AC IN VSTR Drain PWM Sync VFB VCC GND FSQ0465 Rev. 00 Figure 1. Typical Flyback Application Internal Block Diagram Sync 5 Vstr 6 VCC 3 Drain 1 AVS 0.35/0.55 VBurst IFB 3R R tON < tOSP after SS SoftStart PWM OSC VCC Vref VCC good 8V/12V VCC Vref Idelay FB 4 SQ LEB 250ns RQ Gate driver VOSP LPF AOCP VSD VCC VOVP LPF TSD S Q 2 VOCP (1.1V) GND RQ VCC good FSQ0465 Rev.00 Figure 2. Internal Block Diagram © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 3 www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation Pin Configuration 6. VSTR 5. Sync 4. FB 3. VCC 2. GND 1. Drain FSQ0465 Rev.00 Figure 3. Pin Configuration (Top View) Pin Definitions Pin # 1 2 3 Name Drain GND VCC Description SenseFET Drain. High-voltage power SenseFET drain connection. Ground. This pin is the control ground and the SenseFET source. Power Supply. This pin is the positive supply input, providing internal operating current for both startup and steady-state operation. Feedback. This pin is internally connected to the inverting input of the PWM comparator. The collector of an opto-coupler is typically tied to this pin. For stable operation, a capacitor should be placed between this pin and GND. If the voltage of this pin reaches 6V, the overload protection triggers, which shuts down the FPS. Sync. This pin is internally connected to the sync-detect comparator for quasi-resonant switching. In normal quasi-resonant operation, the threshold of the sync comparator is 1.2V/1.0V. Startup. This pin is connected directly, or through a resistor, to the high-voltage DC link. At startup, the internal high-voltage current source supplies internal bias and charges the external capacitor connected to the VCC pin. Once VCC reaches 12V, the internal current source is disabled. It is not recommended to connect Vstr and Drain together. 4 FB 5 Sync 6 Vstr © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 4 www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation Absolute Maximum Ratings Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratings are stress ratings only. TA = 25°C, unless otherwise specified. Symbol Vstr VDS VCC VFB VSync IDM IDSW EAS PD TJ TA TSTG ESD Vstr Pin Voltage Drain Pin Voltage Supply Voltage Parameter Min. 500 650 Max. Unit V V 20 -0.3 -0.3 13.0 13.0 9.6 TC = 25°C 4.0 120 45 Internally limited -25 -55 2.0 2.0 +85 +150 V V V A A mJ W °C °C °C kV kV Feedback Voltage Range Sync Pin Voltage Drain Current Pulsed Continuous Drain Switching Current(6) Single Pulsed Avalanche Energy(7) Total Power Dissipation (TC=25°C) Operating Junction Temperature Operating Ambient Temperature Storage Temperature Human Body Model, JESD22-A114 Charged Device Model, JESD22-C101 Notes: 6. Repetitive peak switching current when inductor load is assumed: limited by maximum duty and maximum junction temperature. IDS DMAX fSW 7. 7. L=14mH, starting TJ=25°C. Thermal Impedance TA = 25°C unless otherwise specified. Symbol θJA θJC Parameter Junction-to-Ambient Thermal Junction-to-Case Thermal Resistance(8) Resistance(9) Package TO-220F-6L Value 50 2.8 Unit °C/W °C/W Notes: 8. Free-standing with no heat-sink under natural convection. 9. Infinite cooling condition - refer to the SEMI G30-88. © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 5 www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation Electrical Characteristics TA = 25°C unless otherwise specified. Symbol SENSEFET SECTION BVDSS IDSS RDS(ON) COSS td(on) tr td(off) tf tON.MAX tB tW fS ΔfS tAVS VAVS tSW IFB DMIN VSTART VSTOP tS/S VOVP VBURH VBURL Hysteresis Parameter Drain Source Breakdown Voltage Zero-Gate-Voltage Drain Current Drain-Source On-State Resistance Output Capacitance Turn-On Delay Time Rise Time Turn-Off Delay Time Fall Time Maximum On Time Blanking Time Detection Time Window Initial Switching Frequency Switching Frequency Variation(11) AVS Triggering Threshold(11) On Time Feedback Voltage Condition VCC = 0V, ID = 100µA VDS = 560V TJ = 25°C, ID = 0.5A VGS = 0V, VDS = 25V, f = 1MHz VDD = 350V, ID = 25mA VDD = 350V, ID = 25mA VDD = 350V, ID = 25mA VDD = 350V, ID = 25mA TJ = 25°C TJ = 25°C, Vsync = 5V TJ = 25°C, Vsync = 0V Min. Typ. Max. Unit 650 250 2.2 60 12 20 30 16 8.8 13.5 59.6 10.0 15.0 6.0 66.7 ±5 4.0 1.2 13.5 700 11 900 12 8 17.5 18 0.45 19 0.55 0.35 200 20 0.65 0.45 20.5 1100 0 13 9 7 75.8 ±10 11.2 16.5 2.6 V µA Ω pF ns ns ns ns µs µs µs kHz % µs V µs µA % V V ms V V V mV CONTROL SECTION -25°C < TJ < 85°C at VIN = 240VDC, Lm = 360μH (AVS triggered when VAVS > spec. and tAVS < spec.) Sync = 500kHz sine input VFB = 1.2V, tON = 4.0µs VFB = 0V VFB = 0V After turn-on With free-running frequency Switching Time Variance by AVS(11) Feedback Source Current Minimum Duty Cycle UVLO Threshold Voltage Internal Soft-Start Time Over-Voltage Protection BURST-MODE SECTION Burst-Mode Voltages TJ = 25°C, tPD = 200ns (10) 0.25 Continued on the following page... © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 6 www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation Electrical Characteristics (Continued) TA = 25°C unless otherwise specified. Symbol PROTECTION SECTION ILIMIT ILIMIT VSD IDELAY tLEB tOSP VOSP tOSP_FB TSD Hys VSH1 VSL1 tsync VSH2 VSL2 VCLAMP Parameter Peak Current Limit of FSQ0465RS Peak Current Limit of FSQ0465RB Shutdown Feedback Voltage Shutdown Delay Current Leading-Edge Blanking Time(11) Threshold Time Condition TJ = 25°C, di/dt = 480mA/µs TJ = 25°C, di/dt = 370mA/µs VCC = 15V VFB = 5V Min. Typ. Max. Unit 1.6 2.64 5.5 4 1.8 3.00 6.0 5 250 1.2 1.8 2.0 2.0 2.5 +60 1.0 0.8 4.3 4.0 0.0 1.2 1.0 230 4.7 4.4 0.4 1.4 1.2 5.1 4.8 0.8 3.0 1.4 2.0 3.36 6.5 6 A A V µA ns µs V µs °C Output Short Threshold Feedback Protection(11) Voltage Thermal Shutdown(11) Hysteresis TJ = 25°C OSP triggered when tON < tOSP, VFB > VOSP and lasts longer than Feedback Blanking Time tOSP_FB Shutdown Temperature +125 +140 +155 SYNC SECTION Sync Threshold Voltage 1 Sync Delay Time(11)(12) Sync Threshold Voltage 2 Low Clamp Voltage VCC = 15V, VFB = 2V ISYNC_MAX = 800µA, ISYNC_MIN = 50µA VCC = 13V VCC = 10V (before VCC reaches VSTART) VCC = 0V, VSTR = minimum 50V VCC = 15V, VFB = 2V V ns V V TOTAL DEVICE SECTION IOP ISTART ICH VSTR Operating Supply Current Start Current Startup Charging Current Minimum VSTR Supply Voltage 1 350 0.65 3 450 0.85 26 5 550 1.00 mA µA mA V Notes: 10. Propagation delay in the control IC. 11. Guaranteed by design; not tested in production. 12. Includes gate turn-on time. © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 7 www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation Comparison Between FSDM0x65RNB and FSQ-Series Function Operation Method FSDM0x65RE Constant Frequency PWM Frequency Modulation FSQ-Series Quasi-Resonant Operation Reduced EMI Noise FSQ-Series Advantages ! Improved efficiency by valley switching ! Reduced EMI noise ! Reduced components to detect valley point ! Valley Switching ! Inherent Frequency Modulation ! Alternate Valley Switching EMI Reduction Hybrid Control Burst-Mode Operation Strong Protections TSD Burst-Mode Operation OLP, OVP 145°C without Hysteresis CCM or AVS Based on Load ! Improves efficiency by introducing hybrid control and Input Condition Advanced Burst-Mode Operation OLP, OVP, AOCP, OSP 140°C with 60°C Hysteresis ! Improved standby power by advanced burst-mode ! Improved reliability through precise AOCP ! Improved reliability through precise OSP ! Stable and reliable TSD operation ! Converter temperature range © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 8 www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation Typical Performance Characteristics These characteristic graphs are normalized at TA= 25°C. Normalized 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Normalized 1.2 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Figure 4. Operating Supply Current (IOP) vs. TA Temperature [°C] Figure 5. UVLO Start Threshold Voltage (VSTART) vs. TA Normalized 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Normalized 1.2 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Figure 6. UVLO Stop Threshold Voltage (VSTOP) vs. TA Temperature [°C] Figure 7. Startup Charging Current (ICH) vs. TA Normalized 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Normalized 1.2 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Figure 8. Initial Switching Frequency (fS) vs. TA Temperature [°C] Figure 9. Maximum On Time (tON.MAX) vs. TA © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 9 www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation Typical Performance Characteristics (Continued) These characteristic graphs are normalized at TA= 25°C. Normalized 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Normalized 1.2 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Figure 10. Blanking Time (tB) vs. TA Temperature [°C] Figure 11. Feedback Source Current (IFB) vs. TA Normalized 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Normalized 1.2 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Figure 12. Shutdown Delay Current (IDELAY) vs. TA Temperature [°C] Figure 13. Burst-Mode High Threshold Voltage (Vburh) vs. TA Normalized 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Normalized 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Figure 14. Burst-Mode Low Threshold Voltage (Vburl) vs. TA | Temperature [°C] Figure 15. Peak Current Limit (ILIM) vs. TA © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 10 www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation Typical Performance Characteristics (Continued) These characteristic graphs are normalized at TA= 25°C. Normalized 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Normalized 1.2 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Figure 16. Sync High Threshold Voltage 1 (VSH1) vs. TA Temperature [°C] Figure 17. Sync Low Threshold Voltage 1 (VSL1) vs. TA Normalized 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Normalized 1.2 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Figure 18. Shutdown Feedback Voltage (VSD) vs. TA Temperature [°C] Figure 19. Over-Voltage Protection (VOV) vs. TA Normalized 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Normalized 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Figure 20. Sync High Threshold Voltage 2 (VSH2) vs. TA Temperature [°C] Figure 21. Sync Low Threshold Voltage 2 (VSL2) vs. TA © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 11 www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation Functional Description 1. Startup: At startup, an internal high-voltage current source supplies the internal bias and charges the external capacitor (Ca) connected to the VCC pin, as illustrated in Figure 22. When VCC reaches 12V, the FPS™ begins switching and the internal high-voltage current source is disabled. The FPS continues its normal switching operation and the power is supplied from the auxiliary transformer winding unless VCC goes below the stop voltage of 8V. VDC CVCC 2.1 Pulse-by-Pulse Current Limit: Because currentmode control is employed, the peak current through the SenseFET is limited by the inverting input of PWM comparator (VFB*), as shown in Figure 23. Assuming that the 0.9mA current source flows only through the internal resistor (3R + R = 2.8k), the cathode voltage of diode D2 is about 2.5V. Since D1 is blocked when the feedback voltage (VFB) exceeds 2.5V, the maximum voltage of the cathode of D2 is clamped at this voltage, clamping VFB*. Therefore, the peak value of the current through the SenseFET is limited. 2.2 Leading-Edge Blanking (LEB): At the instant the internal SenseFET is turned on, a high-current spike usually occurs through the SenseFET, caused by primary-side capacitance and secondary-side rectifier reverse recovery. Excessive voltage across the Rsense resistor would lead to incorrect feedback operation in the current-mode PWM control. To counter this effect, the FPS employs a leading-edge blanking (LEB) circuit. This circuit inhibits the PWM comparator for a short time (tLEB) after the SenseFET is turned on Pulse-WidthModulation (PWM) Circuit 3. Synchronization: The FSQ-series employs a quasiresonant switching technique to minimize the switching noise and loss. The basic waveforms of the quasiresonant converter are shown in Figure 25. To minimize the MOSFET's switching loss, the MOSFET should be turned on when the drain voltage reaches its minimum value, which is indirectly detected by monitoring the VCC winding voltage, as shown in Figure 24. Vds VCC 3 6 VSTR Istart VREF 8V/12V Vcc good Internal Bias FSQ0465 Rev.00 Figure 22. Startup Circuit 2. Feedback Control: FPS employs current-mode control, as shown in Figure 23. An opto-coupler (such as the FOD817A) and shunt regulator (such as the KA431) are typically used to implement the feedback network. Comparing the feedback voltage with the voltage across the Rsense resistor makes it possible to control the switching duty cycle. When the reference pin voltage of the shunt regulator exceeds the internal reference voltage of 2.5V, the opto-coupler LED current increases, pulling down the feedback voltage and reducing the duty cycle. This typically happens when the input voltage is increased or the output load is decreased. VCC Idelay VREF IFB OSC V RO VRO V DC Vsync TF V ovp (8V) VO H11A817A VFB CB 4 D1 D2 + VFB* 3R SenseFET 1.2V 1.0V 230ns Delay MOSFET Gate R Gate driver KA431 - VSD FSQ0465 Rev.00 OLP Rsense ON ON FSQ0465 Rev.00 Figure 23. Pulse-Width-Modulation (PWM) Circuit Figure 24. Quasi-Resonant Switching Waveforms © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 12 www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation The switching frequency is the combination of blank time (tB) and detection time window (tW). In case of a heavy load, the sync voltage remains flat after tB and waits for valley detection during tW. This leads to a low switching frequency not suitable for heavy loads. To correct this drawback, additional timing is used. The timing conditions are described in Figures 25, 26, and 27. When the Vsync remains flat higher than 4.4V at the end of tB which is instant tX, the next switching cycle starts after internal delay time from tX. In the second case, the next switching occurs on the valley when the Vsync goes below 4.4V within tB. Once Vsync detects the first valley in tB, the other switching cycle follows classical QRC operation. t B =15µs tX t B =15µs tX ID S I DS V DS ingnore 4.4V V sync 1.2V 1.0V FS Q 0465 R ev.00 internal delay I DS I DS Figure 27. After Vsync Finds First Valley 4. Protection Circuits: The FSQ-series has several self-protective functions, such as Overload Protection (OLP), Abnormal Over-Current Protection (AOCP), Over-Voltage Protection (OVP), and Thermal Shutdown (TSD). All the protections are implemented as autorestart mode. Once the fault condition is detected, switching is terminated and the SenseFET remains off. This causes VCC to fall. When VCC falls down to the Under-Voltage Lockout (UVLO) stop voltage of 8V, the protection is reset and the startup circuit charges the VCC capacitor. When the VCC reaches the start voltage of 12V, normal operation resumes. If the fault condition is not removed, the SenseFET remains off and VCC drops to stop voltage again. In this manner, the auto-restart can alternately enable and disable the switching of the power SenseFET until the fault condition is eliminated. Because these protection circuits are fully integrated into the IC without external components, reliability is improved without increasing cost. V DS Power on Fault occurs Fault rem oved V DS 4.4V V sync 1.2V 1.0V FSQ 0465 Rev.00 internal delay Figure 25. Vsync > 4.4V at tX tB=15µs tX IDS IDS VDS 4.4V V CC Vsync 1.2V 1.0V FSQ0465 Rev.00 12V 8V internal delay t FSQ0465 Rev.00 Figure 26. Vsync < 4.4V at tX Norm al operation Fault situation Norm al operation Figure 28. Auto Restart Protection Waveforms © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 13 www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation AOCP FSQ0465 Rev.00 Figure 30. Abnormal Over-Current Protection 4.3 Output-Short Protection (OSP): If the output is shorted, steep current with extremely high di/dt can flow through the SenseFET during the LEB time. Such a steep current brings high voltage stress on the drain of SenseFET when turned off. To protect the device from such an abnormal condition, OSP is included in the FSQseries. It is comprised of detecting VFB and SenseFET turn-on time. When the VFB is higher than 2V and the SenseFET turn-on time is lower than 1.2µs, the FPS recognizes this condition as an abnormal error and shuts down PWM switching until VCC reaches Vstart again. An abnormal condition output short is shown in Figure 31. MOSFET Drain Current Rectifier Diode Current Turn-off delay V FB F S Q 0 4 6 5 R e v .0 0 O ve rlo a d p ro te c tio n 6 .0 V VFB 0 Minimum turn-on time D 1.2µs 2 .5 V Vo t 1 2 = C fb *(6 .0 -2 .5 )/I d e la y 0 T1 T2 t Io FSQ0465 Rev. 00 0 Figure 29. Overload Protection 4.2 Abnormal Over-Current Protection (AOCP): When the secondary rectifier diodes or the transformer pins are shorted, a steep current with extremely high di/dt can flow through the SenseFET during the LEB time. Even though the FSQ-series has overload protection, it is not enough to protect the FSQ-series in that abnormal case, since severe current stress is imposed on the SenseFET until OLP triggers. The FSQ-series has an internal AOCP circuit shown in Figure 30. When the gate turn-on signal is applied to the power SenseFET, the AOCP block is enabled and monitors the current through the sensing resistor. The voltage across the resistor is compared with a preset AOCP level. If the sensing resistor voltage is greater than the AOCP level, the set signal is applied to the latch, resulting in the shutdown of the SMPS. Figure 31. Output Short Waveforms 4.4 Over-Voltage Protection (OVP): If the secondary side feedback circuit malfunctions or a solder defect causes an opening in the feedback path, the current through the opto-coupler transistor becomes almost zero. Then, Vfb climbs up in a similar manner to the overload situation, forcing the preset maximum current to be supplied to the SMPS until overload protection is activated. Because more energy than required is provided to the output, the output voltage may exceed the rated voltage before overload protection is activated, resulting in the breakdown of the devices in the secondary side. To prevent this situation, an over-voltage protection (OVP) circuit is employed. In general, VCC is proportional to the output voltage and the FSQ-series uses VCC instead of directly monitoring the output voltage. If VCC exceeds 19V, an OVP circuit is activated, © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 14 + output short occurs - 4.1 Overload Protection (OLP): Overload is defined as the load current exceeding its normal level due to an unexpected abnormal event. In this situation, the protection circuit should trigger to protect the SMPS. However, even when the SMPS is in the normal operation, the overload protection circuit can be triggered during the load transition. To avoid this undesired operation, the overload protection circuit is designed to trigger only after a specified time to determine whether it is a transient situation or a true overload situation. Because of the pulse-by-pulse current limit capability, the maximum peak current through the SenseFET is limited, and therefore the maximum input power is restricted with a given input voltage. If the output consumes more than this maximum power, the output voltage (VO) decreases below the set voltage. This reduces the current through the optocoupler LED, which also reduces the opto-coupler transistor current, thus increasing the feedback voltage (VFB). If VFB exceeds 2.5V, D1 is blocked and the 5µA current source starts to charge CB slowly up to VCC. In this condition, VFB continues increasing until it reaches 6V, when the switching operation is terminated, as shown in Figure 29. The delay time for shutdown is the time required to charge CFB from 2.5V to 6V with 5µA. A 20 ~ 50ms delay time is typical for most applications. 3R OSC PWM LEB 200ns S R Q Q Gate driver R Rsense VOCP 2 GND ILIM www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation resulting in the termination of the switching operation. To avoid undesired activation of OVP during normal operation, VCC should be designed below 19V. 4.5 Thermal Shutdown with Hysteresis (TSD): The SenseFET and the control IC are built in one package. This enables the control IC to detect the abnormally high temperature of the SenseFET. If the temperature exceeds approximately 140°C, the thermal shutdown triggers IC shutdown. The IC recovers its operation when the junction temperature decreases 60°C from TSD temperature and VCC reaches startup voltage (Vstart). 5. Soft-Start: The FPS has an internal soft-start circuit that increases PWM comparator inverting input voltage with the SenseFET current slowly after it starts up. The typical soft-start time is 17.5ms. The pulse width to the power switching device is progressively increased to establish the correct working conditions for transformers, inductors, and capacitors. The voltage on the output capacitors is progressively increased with the intention of smoothly establishing the required output voltage. This mode helps prevent transformer saturation and reduces stress on the secondary diode during startup. 6. Burst Operation: To minimize power dissipation in standby mode, the FPS enters burst-mode operation. As the load decreases, the feedback voltage decreases. As shown in Figure 32, the device automatically enters burst-mode when the feedback voltage drops below VBURL (350mV). At this point, switching stops and the output voltages start to drop at a rate dependent on standby current load. This causes the feedback voltage to rise. Once it passes VBURH (550mV), switching resumes. The feedback voltage then falls and the process repeats. Burst-mode operation alternately enables and disables switching of the power SenseFET, thereby reducing switching loss in standby mode. VO Voset VFB 0.55V 0.35V IDS VDS FSQ0465 Rev. 00 time t1 Switching disabled t2 t3 Switching disabled t4 Figure 32. Waveforms of Burst Operation 7. Switching Frequency Limit: To minimize switching loss and Electromagnetic Interference (EMI), the MOSFET turns on when the drain voltage reaches its minimum value in quasi-resonant operation. However, this causes switching frequency to increases at light load conditions. As the load decreases or input voltage increases, the peak drain current diminishes and the switching frequency increases. This results in severe switching losses at light-load condition, as well as intermittent switching and audible noise. These problems create limitations for the quasi-resonant converter topology in a wide range of applications. To overcome these problems, FSQ-series employs a frequency-limit function, as shown in Figures 33 and Figure 34. Once the SenseFET is turned on, the next turn-on is prohibited during the blanking time (tB). After the blanking time, the controller finds the valley within the detection time window (tW) and turns on the MOSFET, as shown in Figures 33 and Figure 34 (Cases A, B, and C). If no valley is found during tW, the internal SenseFET is forced to turn on at the end of tW (Case D). Therefore, the devices have a minimum switching frequency of 48kHz and a maximum switching frequency of 67kHz. © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 15 www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation tsmax=21μs IDS IDS A tB=15μs ts IDS VDS 8. AVS (Alternating Valley Switching): Due to the quasi-resonant operation with limited frequency, the switching frequency varies depending on input voltage, load transition, and so on. At high input voltage, the switching on time is relatively small compared to low input voltage. The input voltage variance is small and the switching frequency modulation width becomes small. To improve the EMI performance, AVS is enabled when input voltage is high and the switching on time is small. Internally, quasi-resonant operation is divided into two categories; one is first-valley switching and the other is second-valley switching after blanking time. In AVS, two successive occurrences of first-valley switching and the other two successive occurrences of second-valley switching is alternatively selected to maximize frequency modulation. As depicted in Figure 34, the switching frequency hops when the input voltage is high. The internal timing diagram of AVS is described in Figure 35. fs Assume the resonant period is 2 μ s 1 15μs 1 17 μs 1 19 μs 1 21μs IDS B tB=15μs ts VDS IDS VDS tB=15μs ts IDS C 67kHz 59kHz 53kHz 48kHz AVS trigger point Constant frequency Variable frequency within limited range DCM AVS region IDS VDS tB=15μs IDS CCM tW=6μs D D C B A VIN FSQ0465 Rev.00 tsmax=21μs FSQ0465 Rev. 00 Figure 33. QRC Operation with Limited Frequency Figure 34. Switching Frequency Range Vgate Synchronize Synchronize Vgate continued 2 pulses 1st valley switching fixed Vgate continued another 2 pulses 2 nd valley switching fixed fixed fixed Vgate continued 2 pulses 1st valley switching fixed GateX2 One-shot AVS fixed triggering 1st or 2nd is depend on GateX2 de-triggering triggering 1st or 2nd is dependent on GateX2 VDS tB tB tB tB tB tB GateX2: Counting Vgate every 2 pulses independent on other signals . FSQ0465 Rev. 00 1st valley- 2nd valley frequency modulation. Modulation frequency is approximately 17kHz. Figure 35. Alternating Valley Switching (AVS) © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 16 www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation PCB Layout Guide Due to the combined scheme, FPS shows better noise immunity than conventional PWM controller and MOSFET discrete solutions. Furthermore, internal drain current sense eliminates noise generation caused by a sensing resistor. There are some recommendations for PCB layout to enhance noise immunity and suppress the noise inevitable in power-handling components. There are typically two grounds in the conventional SMPS: power ground and signal ground. The power ground is the ground for primary input voltage and power, while the signal ground is ground for PWM controller. In FPS, those two grounds share the same pin, GND. Normally the separate grounds do not share the same trace and meet only at one point, the GND pin. More, wider patterns for both grounds are good for large currents by decreasing resistance. Capacitors at the VCC and FB pins should be as close as possible to the corresponding pins to avoid noise from the switching device. Sometimes Mylar® or ceramic capacitors with electrolytic for VCC is better for smooth operation. The ground of these capacitors needs to connect to the signal ground (not power ground). The cathode of the snubber diode should be close to the Drain pin to minimize stray inductance. The Y-capacitor between primary and secondary should be directly connected to the power ground of DC link to maximize surge immunity. Because the voltage range of feedback and sync line is small, it is affected by the noise of the drain pin. Those traces should not draw across or close to the drain line. When the heat sink is connected to the ground, it should be connected to the power ground. If possible, avoid using jumper wires for power ground and drain. Figure 36. Recommended PCB Layout Mylar® is a registered trademark of DuPont Teijin Films. © 2008 Fairchild Semiconductor Corporation FSQ0465RS/RB Rev. 1.0.1 17 www.fairchildsemi.com FSQ0465RS/RB — Green-Mode Farichild Power Switch (FPS™) for Quasi-Resonant Operation Typical Application Circuit Application LCD Monitor Power Supply FPS™ Device FSQ0465RS Input Voltage Range 85-265VAC Rated Output Power 40W Output Voltage (Maximum Current) 5.0V (2.0A) 13V (2.3A) Features ! Average efficiency of 25%, 50%, 75%, and 100% load conditions is higher than 80% at universal input ! Low standby mode power consumption (