FSQ0365RN

FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Green Mode Fairchild Power Switch (FPS™) for QRC November 2006 FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Green Mode Fairchild Power Switch (FPS™) for Quasi-Resonant Operation - Low EMI and High Efficiency Features Optimized for Quasi-Resonant Converter (QRC) Low EMI through Variable Frequency Control and Inherent Frequency Modulation High-Efficiency through Minimum Voltage Switching Narrow Frequency Variation Range over Wide Load and Input Voltage Variation Advanced Burst-Mode Operation for Low Standby Power Consumption Pulse-by-Pulse Current Limit Various Protection Functions: Overload Protection (OLP), Over-Voltage Protection (OVP), Abnormal Over-Current Protection (AOCP), Internal Thermal Shutdown (TSD) Under-Voltage Lockout (UVLO) with Hysteresis Internal Start-up Circuit Internal High-Voltage Sense FET (650V) Built-in Soft-Start (15ms) 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 with minimal external components. The PWM controller includes an integrated fixed-frequency oscillator, Under-Voltage Lockout, Leading Edge Blanking (LEB), optimized gate driver, internal soft-start, temperature-compensated precise current sources for loop compensation, and self-protection circuitry. Compared with 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 that is well suited for cost-effective designs of quasi-resonant switching flyback converters. Applications Power Supply for DVP Player and DVD Recorder Power supply for Set-Top Box Adapter Auxiliary Power Supply for PC, LCD TV, and PDP TV Ordering Information Maximum Output Power(1) Operating Current RDS(ON) Product PKG. Temp. Limit Max. Number(5) 230VAC±15%(2) Adapter(3) 7W 10W 14W 17.5W 85-265VAC Adapter(3) 6W 9W 11W 13W Open Frame(4) 10W 15W 20W 25W Open Frame(4) 8W 13W 16W 19W Replaces Devices FSDL321 FSDM311 FSDL0165RN FSDM0265RN FSDM0265RNB FSDM0365RN RSDM0365RNB FSQ311 FSQ0165RN FSQ0265RN FSQ0365RN 8-DIP -25 to +85°C 8-DIP -25 to +85°C 8-DIP -25 to +85°C 8-DIP -25 to +85°C 0.6A 0.9A 1.2A 1.5A 19Ω 10Ω 6Ω 4.5Ω Notes: 1. The junction temperature can limit the maximum output power. 2. 230VAC or 100/115VAC with doubler. The maximum power with CCM operation. 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. PB-free package per JEDEC J-STD-020B. FPSTM is a trademark of Fairchild Semiconductor Corporation. © 2006 Fairchild Semiconductor Corporation FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Rev. 1.0.0 www.fairchildsemi.com FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Green Mode Fairchild Power Switch (FPS™) for QRC Application Diagram VO AC IN Vstr PWM Sync FB VCC GND Drain FSQ0365RN Rev.00 Figure 1. Typical Flyback Application Internal Block Diagram Sync 4 + 0.7V/0.2V + VCC Vref Idelay IFB 3R R SoftStart PWM LEB 200ns S Q Gate driver 0.35/0.55 VBurst OSC + Vref VCC good 8V/12V Vstr 5 VCC 2 Drain 67 8 FB 3 RQ AOCP 6V VSD Sync Vovp 6V VCC good FSQ0365RN Rev.00 TSD 2.5μs time delay S 1 Q VOCP (1.1V) GND RQ Figure 2. Internal Block Diagram © 2006 Fairchild Semiconductor Corporation FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Rev. 1.0.0 2 www.fairchildsemi.com FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Green Mode Fairchild Power Switch (FPS™) for QRC Pin Configuration GND VCC 8-DIP FB Sync D D D Vstr FSQ0365RN Rev.00 Figure 3. Pin Configuration (Top View) Pin Definitions Pin # 1 2 Name GND VCC Description Ground. This pin is the control ground and the SenseFET source. Power Supply. This pin is the positive supply input. This pin provides internal operating current for both start-up 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 quasiresonant switching. In normal quasi-resonant operation, the threshold of the sync comparator is 0.7V/0.2V. Start-up. This pin is connected directly to the high-voltage DC link. At start-up, 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. SenseFET drain. High-voltage power SenseFET drain connection. SenseFET drain. High-voltage power SenseFET drain connection. SenseFET drain. High-voltage power SenseFET drain connection. 3 FB 4 Sync 5 6 7 8 Vstr Drain Drain Drain © 2006 Fairchild Semiconductor Corporation FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Rev. 1.0.0 3 www.fairchildsemi.com FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Green Mode Fairchild Power Switch (FPS™) for QRC Absolute Maximum Ratings The “Absolute Maximum Ratings” are those values beyond which the safety of the device cannot be guaranteed. The device should not be operated at these limits. The parametric values defined in the Electrical Characteristics tables are not guaranteed at the absolute maximum ratings. TA = 25°C, unless otherwise specified. Symbol Vstr VDS VCC VFB VSync Vstr Pin Voltage Drain Pin Voltage Supply Voltage Parameter Min. 500 650 Max. Unit V V 20 -0.3 -0.3 FSQ0365RN FSQ0265RN FSQ0165RN FSQ311 FSQ0365RN FSQ0265RN FSQ0165RN FSQ311 9.0 9.0 12 8 4 1.5 230 140 50 10 1.5 Internally limited -25 -55 (8) (8) V V V Feedback Voltage Range Sync Pin Voltage IDM Drain Current Pulsed(6) A EAS Single Pulsed Avalanche Energy(7) mJ PD TJ TA TSTG Total Power Dissipation Operating Junction Temperature Operating Ambient Temperature Storage Temperature ESD Capability, HBM Model ESD Capability, Machine Model W °C °C °C 85 150 CLASS1 C CLASS B Notes: 6. Repetitive rating: Pulse width limited by maximum junction temperature. 7. L=14mH, starting TJ=25°C. 8. Meets JEDEC Standards JESD 22-A114 and 22-A115. Thermal Impedance(9) Symbol 8-DIP θJA(10) θJC(11) θJT(12) Junction-to-Ambient Thermal Resistance Junction-to-Case Thermal Resistance Junction-to-Top Thermal Resistance 80 20 35 °C/W Parameter Value Unit Notes: 9. All items are tested with the standards JESD 51-2 and 51-10 (DIP). 10. Free-standing, with no heat-sink, under natural convection. 11. Infinite cooling condition - refer to the SEMI G30-88. 12. Measured on the PKG top surface. © 2006 Fairchild Semiconductor Corporation FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Rev. 1.0.0 4 www.fairchildsemi.com FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Green Mode Fairchild Power Switch (FPS™) for QRC Electrical Characteristics TA = 25°C unless otherwise specified. Symbol SENSEFET SECTION BVDSS IDSS Parameter Drain Source Breakdown Voltage Zero-Gate-Voltage Drain Current FSQ0365RN Drain-Source onState Resistance FSQ0265RN FSQ0165RN FSQ311 FSQ0365RN FSQ0265RN FSQ0165RN FSQ311 FSQ0365RN FSQ0265RN FSQ0165RN FSQ311 FSQ0365RN Reverse Transfer Capacitance FSQ0265RN FSQ0165RN FSQ311 FSQ0365RN FSQ0265RN FSQ0165RN FSQ311 FSQ0365RN FSQ0265RN FSQ0165RN FSQ311 FSQ0365RN FSQ0265RN FSQ0165RN FSQ311 FSQ0365RN FSQ0265RN FSQ0165RN FSQ311 Condition VCC = 0V, ID = 100µA VDS = 560V Min. Typ. Max. Unit 650 100 3.5 4.5 6.0 10.0 19.0 Ω 5.0 8.0 14.0 315 550 250 162 47 38 25 18 9.0 17.0 10.0 3.8 11.2 20.0 12.0 9.5 34 15 4 19 28.3 55.0 30.0 33.0 32 25 10 42 V µA RDS(ON) TJ = 25°C, ID = 0.5A CSS Input Capacitance VGS = 0V, VDS = 25V, f = 1MHz pF COSS Output Capacitance VGS = 0V, VDS = 25V, f = 1MHz pF CRSS VGS = 0V, VDS = 25V, f = 1MHz pF td(on) Turn-On Delay Time VDD = 350V, ID = 25mA ns tr Rise Time VDD = 350V, ID = 25mA ns td(off) Turn-Off Delay Time VDD = 350V, ID = 25mA ns tf Fall Time VDD = 350V, ID = 25mA ns © 2006 Fairchild Semiconductor Corporation FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Rev. 1.0.0 5 www.fairchildsemi.com FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Green Mode Fairchild Power Switch (FPS™) for QRC Electrical Characteristics (Continued) TA = 25°C unless otherwise specified. Symbol CONTROL SECTION tON.MAX tB tW fS ΔfS IFB DMIN VSTART VSTOP tS/S VBURH VBURL Hysteresis PROTECTION SECTION Parameter Maximum ON Time Blanking Time Detection Time Window Initial Switching Frequency Switching Frequency Minimum Duty Cycle UVLO Threshold Voltage Internal Soft-Start Time Variation(13) Condition TJ = 25°C TJ = 25°C, Vsync = 0V Min. Typ. Max. Unit 10.5 13.2 50.5 12.0 15.0 3.0 55.6 ±5 700 11 900 12 8 15 0.45 0.25 0.55 0.35 200 0.65 0.45 61.7 ±10 1100 0 13 9 7 13.5 16.8 µsec µsec µsec kHz % µA % V V ms V V mV 1.68 1.34 1.0 0.67 6.5 6 6.5 4 155 0.85 0.26 V µA ns V µsec °C V V ns A -25°C < TJ < 85°C VFB = 0V VFB = 0V After turn-on With free-running frequency TJ = 25°C, tPD = 200ns(14) Feedback Source Current BURST-MODE SECTION Burst-Mode Voltages FSQ0365RN ILIMIT Peak Current Limit FSQ0265RN FSQ0165RN FSQ311 VSD IDELAY tLEB VOVP tOVP TSD VSH VSL tsync IOP ISTART ICH VSTR Shutdown Feedback Voltage Shutdown Delay Current Leading-Edge Blanking Time(13) Over-Voltage Protection Over-Voltage Protection Blanking Time Thermal Shutdown Temperature(13) TJ = 25°C, di/dt = 240mA/µsec TJ = 25°C, di/dt = 200mA/µsec TJ = 25°C, di/dt = 150mA/µsec TJ = 25°C, di/dt = 100mA/µsec VCC = 15V VFB = 5V VCC = 15V, VFB = 2V 1.32 1.06 0.8 0.53 5.5 4 5.5 2 125 0.55 0.14 1.50 1.20 0.9 0.60 6.0 5 200 6.0 3 140 0.70 0.20 300 SYNC SECTION Sync Threshold Voltage Sync Delay Time(13)(15) TOTAL DEVICE SECTION Operating Supply Current (Control Part Only) Start Current Start-up Charging Current Minimum VSTR Supply Voltage VCC = 15V VCC = VSTART - 0.1V (before VCC reaches VSTART) VCC = 0V, VSTR = min. 40V 1 270 0.65 3 360 0.85 26 5 450 1.00 mA µA mA V Notes: 13. Though guaranteed, it is not tested in the mass production. 14. Propagation delay in the control IC. 15. Include gate turn-on time. © 2006 Fairchild Semiconductor Corporation FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Rev. 1.0.0 6 www.fairchildsemi.com FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Green Mode Fairchild Power Switch (FPS™) for QRC Comparison Between FSDM0x65RNB and FSQ-Series Function Operation method EMI reduction FSDM0x65RNB Constant frequency PWM Frequency modulation FSQ-Series Quasi-resonant operation Valley switching & inherent frequency modulation FSQ-Series Advantages Improved efficiency by valley switching Reduced EMI noise Reduce EMI noise by two ways Burst-mode operation Fixed burst peak Advanced burst-mode Improved standby power by valley switching also in burst-mode Because the current peak during burst operation is dependent on VFB, it is easier to solve audible noise Improved reliability through precise abnormal over-current protection Protection AOCP © 2006 Fairchild Semiconductor Corporation FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Rev. 1.0.0 7 www.fairchildsemi.com FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Green Mode Fairchild Power Switch (FPS™) for QRC Typical Performance Characteristics These characteristic graphs are normalized at TA= 25°C. 1.2 1.0 1.2 1.0 Normalized 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Normalized 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Temperature [°C] Figure 4. Operating Supply Current (IOP) vs. TA Figure 5. UVLO Start Threshold Voltage (VSTART) vs. TA 1.2 1.0 1.2 1.0 Normalized 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Normalized 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Temperature [°C] Figure 6. UVLO Stop Threshold Voltage (VSTOP) vs. TA Figure 7. Start-up Charging Current (ICH) vs. TA 1.2 1.0 1.2 1.0 Normalized 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Normalized 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Temperature [°C] Figure 8. Initial Switching Frequency (fS) vs. TA © 2006 Fairchild Semiconductor Corporation FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Rev. 1.0.0 8 Figure 9. Maximum On Time (tON.MAX) vs. TA www.fairchildsemi.com FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Green Mode Fairchild Power Switch (FPS™) for QRC Typical Performance Characteristics (Continued) These characteristic graphs are normalized at TA= 25°C. 1.2 1.0 1.2 1.0 Normalized 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Normalized 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Temperature [°C] Figure 10. Blanking Time (tB) vs. TA Figure 11. Feedback Source Current (IFB) vs. TA 1.2 1.0 1.2 1.0 Normalized Normalized 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Temperature [°C] Figure 12. Shutdown Delay Current (IDELAY) vs. TA Figure 13. Burst-Mode High Threshold Voltage (Vburh) vs. TA 1.2 1.0 1.2 1.0 Normalized Normalized 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Temperature [°C] Figure 14. Burst-Mode Low Threshold Voltage (Vburl) vs. TA Figure 15. Peak Current Limit (ILIM) vs. TA © 2006 Fairchild Semiconductor Corporation FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Rev. 1.0.0 9 www.fairchildsemi.com FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Green Mode Fairchild Power Switch (FPS™) for QRC Typical Performance Characteristics (Continued) These characteristic graphs are normalized at TA= 25°C. 1.2 1.0 1.2 1.0 Normalized 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Normalized 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Temperature [°C] Figure 16. Sync High Threshold Voltage (VSH) vs. TA Figure 17. Sync Low Threshold Voltage (VSL) vs. TA 1.2 1.0 1.2 1.0 Normalized 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Normalized 0.8 0.6 0.4 0.2 0.0 -25 0 25 50 75 100 125 Temperature [°C] Temperature [°C] Figure 18. Shutdown Feedback Voltage (VSD) vs. TA Figure 19. Over-Voltage Protection (VOV) vs. TA © 2006 Fairchild Semiconductor Corporation FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Rev. 1.0.0 10 www.fairchildsemi.com FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Green Mode Fairchild Power Switch (FPS™) for QRC 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 20. 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. 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. VCC Idelay Vref IFB OSC VDC VO FOD817A VFB CB 3 D1 D2 3R + VFB* R SenseFET Ca KA431 Gate driver - VCC 2 ICH Vref 8V/12V VCC good Internal Bias 5 Vstr VSD FSQ0365RN Rev. 00 OLP Rsense Figure 21. Pulse-Width-Modulation (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 22. To minimize the MOSFET's switching loss, the MOSFET should be turned on when the drain voltage reaches its minimum value, as shown in Figure 22. The minimum drain voltage is indirectly detected by monitoring the VCC winding voltage, as shown in Figure 22. Vds FSQ0365RN Rev.00 Figure 20. Start-up Circuit 2. Feedback Control: FPS employs current mode control, as shown in Figure 21. 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, thus pulling down the feedback voltage and reducing the duty cycle. This event typically happens when the input voltage is increased or the output load is decreased. 2.1 Pulse-by-Pulse Current Limit: Because current mode control is employed, the peak current through the SenseFET is limited by the inverting input of PWM comparator (VFB*), as shown in Figure 21. 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, thus clamping VFB*. Therefore, the peak value of the current through the SenseFET is limited. VRO VRO VDC Vsync tF Vovp (6V) 0.7V 0.2V 300ns Delay MOSFET Gate ON ON FSQ0365RN Rev.00 Figure 22. Quasi-Resonant Switching Waveforms www.fairchildsemi.com 11 © 2006 Fairchild Semiconductor Corporation FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Rev. 1.0.0 FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Green Mode Fairchild Power Switch (FPS™) for QRC 4. Protection Circuits: The FSQ-series has several self-protective functions, such as Overload Protection (OLP), Abnormal Over-Current protection (AOCP), OverVoltage 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 start-up circuit charges VCC capacitor. When the VCC reaches the start voltage of 12V, the FSQ-series resumes normal operation. 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, the reliability is improved without increasing cost. Fault occurs 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 2.8V, 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 24. The delay time for shutdown is the time required to charge CB from 2.8V to 6V with 5µA. A 20 ~ 50ms delay time is typical for most applications. VFB 6.0V FSQ0365RN Rev.00 Overload protection 2.8V Power on Fault removed VDS t12= CFB*(6.0-2.8)/Idelay t1 t2 t Figure 24. 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 OLP (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 (Abnormal Over-Current Protection) circuit as shown in Figure 25. 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. 3R VCC 12V 8V t FSQ0365RN Rev. 00 Normal operation Fault situation Normal operation Figure 23. Auto Restart Protection Waveforms 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 Sense FET is limited, and therefore the maximum input power is restricted with a given input OSC PWM LEB 200ns S R Q Q Gate driver R Rsense 1 GND VOCP AOCP FSQ0365RN Rev.00 - Figure 25. Abnormal Over-Current Protection © 2006 Fairchild Semiconductor Corporation FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Rev. 1.0.0 12 www.fairchildsemi.com + FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Green Mode Fairchild Power Switch (FPS™) for QRC 4.3 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 the overload protection triggers. Because more energy than required is provided to the output, the output voltage may exceed the rated voltage before the overload protection triggers, resulting in the breakdown of the devices in the secondary side. To prevent this situation, an OVP circuit is employed. In general, the peak voltage of the sync signal is proportional to the output voltage and the FSQ-series uses a sync signal instead of directly monitoring the output voltage. If the sync signal exceeds 6V, an OVP is triggered, shutting down the SMPS. To avoid undesired triggering of OVP during normal operation, the peak voltage of the sync signal should be designed below 6V. 4.4 Thermal Shutdown (TSD): The SenseFET and the control IC are built in one package. This makes it easy for the control IC to detect the abnormal over temperature of the SenseFET. If the temperature exceeds ~150°C, the thermal shutdown triggers. 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 15ms, 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 26, 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 time FSQ0365RN Rev.00 t1 Switching disabled t2 t3 Switching disabled t4 Figure 26. Waveforms of Burst Operation 7. Switching Frequency Limit: To minimize switching loss and EMI (Electromagnetic Interference), 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, 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. Because of these problems, the quasi-resonant converter topology has limitations in a wide range of applications. To overcome this problem, FSQ-series employs a frequency-limit function, as shown in Figures 27 and 28. 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 27 and 28 (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, our devices have a minimum switching frequency of 55kHz and a maximum switching frequency of 67kHz, as shown in Figure 28. © 2006 Fairchild Semiconductor Corporation FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Rev. 1.0.0 13 www.fairchildsemi.com FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Green Mode Fairchild Power Switch (FPS™) for QRC tsmax=18μs IDS IDS When the resonant period is 2μs 67kHz A B 59kHz 55kHz C Constant frequency A tB=15μs ts D Burst mode IDS IDS B tB=15μs ts FSQ0365RN Rev. 00 PO Figure 28. Switching Frequency Range IDS IDS C tB=15μs ts IDS IDS tB=15μs D tW=3μs tsmax=18μs FSQ0365RN Rev. 00 Figure 27. QRC Operation with Limited Frequency © 2006 Fairchild Semiconductor Corporation FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Rev. 1.0.0 14 www.fairchildsemi.com FSQ0365RN, FSQ0265RN, FSQ0165RN, FSQ311 Green Mode Fairchild Power Switch (FPS™) for QRC Application Information Application DVD Player Power Supply FPS Device Input Voltage Range 85-265VAC Rated Output Power Output Voltage (Max. Current) 5.1V (1.0A) 3.4V (1.0A) 12V (0.4A) 16V (0.3A) FSQ0365RN 19W Features High efficiency ( >77% at universal input) Low standby mode power consumption (