FSCQ1265RTYDTU

DATA SHEET www.onsemi.com Green Mode Fairchild Power Switch (FPSt) FSCQ Series FSCQ0765RT / FSCQ0965RT / FSCQ1265RT / FSCQ1565RT TO−220−5 CASE 340BH MARKING DIAGRAM Description A Quasi−Resonant Converter (QRC) typically shows lower EMI and higher power conversion efficiency compared to a conventional hard−switched converter with a fixed switching frequency. Therefore, a QRC is well suited for noise−sensitive applications, such as color TV and audio. Each product in the FSCQ series contains an integrated Pulse Width Modulation (PWM) controller and a SENSEFET®. This series is specifically designed for quasi−resonant off−line Switch Mode Power Supplies (SMPS) 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 a discrete MOSFET and PWM controller solution, the FSCQ series can reduce total cost, component count, size, and weight; while increasing efficiency, productivity, and system reliability. These devices provide a basic platform for cost−effective designs of quasi−resonant switching flyback converters. Features • Optimized for Quasi−Resonant Converter (QRC) • Advanced Burst−Mode Operation for under 1 W Standby Power • • • • • • • • • • • $Y&Z&3&K CQxx65RT $Y &Z &3 &K CQXX65RT XX = onsemi Logo = Assembly Plant Code = Date Code (Year & Week) = Lot Code = Specific Device Code = 07, 09, 12, 15 ORDERING INFORMATION See detailed ordering and shipping information on page 31 of this data sheet. Consumption Pulse−by−Pulse Current Limit Overload Protection (OLP) – Auto Restart Over−Voltage Protection (OVP) – Auto Restart Abnormal Over−Current Protection (AOCP) – Latch Internal Thermal Shutdown (TSD) – Latch Under−Voltage Lockout (UVLO) with Hysteresis Low Startup Current (Typical: 25 mA) Internal High Voltage SENSEFET Built−in Soft−Start (20 ms) Extended Quasi−Resonant Switching This is a Pb−Free and Halid−Free Device Applications • CTV • Audio Amplifier Related Resources • https://www.onsemi.com/pub/Collateral/AN−4146.pdf • https://www.onsemi.com/pub/Collateral/AN−4140.pdf © Semiconductor Components Industries, LLC, 2006 September, 2021 − Rev. 2 1 Publication Order Number: FSCQ1565RT/D FSCQ Series VO AC IN Drain FSCQ−Series PWM GND Sync VFB VCC Figure 1. Typical Flyback Application Table 1. MAXIMUM OUTPUT POWER (Note 1) 230 VAC +15% (Note 2) 85−265 VAC Product Open Frame (Note 3) Open Frame (Note 3) FSCQ0765RT 100 W 85 W FSCQ0965RT 130 W 110 W FSCQ1265RT 170 W 140 W FSCQ1565RT 210 W 170 W 1. The junction temperature can limit the maximum output power. 2. 230 VAC or 100/115 VAC with doubler. 3. Maximum practical continuous power in an open frame design at 50°C ambient. www.onsemi.com 2 FSCQ Series Internal Block Diagram Sync 5 Vcc 3 + Threshold Soft Start Normal Operation Auxiliary Vref Burst Switching Vref Vref IBFB IFB 9 V/15 V Vcc good Main Bias Normal Operation Vref Internal Bias IB PWM 4 2.5 R R S Q R Q Gate Driver LEB 600 ns VSD Sync Vovp − OSC Idelay VFB + fs 4.6 V/2.6 V: Normal QR 3.0 V/1.8 V: Extended QR Burst Mode Controller VBurst Vcc Quasi−Resonant (QR) Switching Controller − Drain 1 S Vcc good (Vcc = 9 V) R Q Q AOCP Q S Q R Figure 2. Functional Block Diagram www.onsemi.com 3 2 GND TSD Vocp Power Off Reset (Vcc = 6 V) FSCQ Series Pin Configuration 5 4 3 2 SYNC VFB VCC GND 1 DRAIN Figure 3. Pin Assignments (Top View) PIN DESCRIPTION ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ Pin No. Symbol Description 1 DRAIN 2 GND This pin is the control ground and the SENSEFET source. 3 VCC This pin is the positive supply input. This pin provides internal operating current for both startup and steady−state operation. 4 VFB 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 7.5 V, the overload protection triggers, which results in the FPS] shutting down. 5 SYNC This pin is the high−voltage power SENSEFET drain connection. 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 4.6 V / 2.6 V. Whereas, the sync threshold is changed to 3.0 V / 1.8 V in an extended quasi−resonant operation. ABSOLUTE MAXIMUM RATINGS (TA = 25°C unless otherwise specified) Parameter Symbol Value Unit Drain Pin Voltage VDS 650 V Supply Voltage VCC 20 V Analog Input Voltage Range Vsync −0.3 to 13 V VFB −0.3 to VCC IDM 15.2 Drain Current Pulsed (Note 4) FSCQ0765RT Continuous Drain Current (TC = 25°C) (TC: Case Back Surface Temperature) FSCQ0965RT 16.4 FSCQ1265RT 21.2 FSCQ1565RT 26.4 FSCQ0765RT Continuous Drain Current* (TDL = 25°C) (TDL: Case Back Surface Temperature) ID FSCQ0965RT 4.1 FSCQ1265RT 5.3 FSCQ1565RT 6.6 FSCQ0765RT ID* 7.6 FSCQ1265RT 11.0 FSCQ0765RT A(rms) A(rms) 13.3 ID 2.4 FSCQ0965RT 2.6 FSCQ1265RT 3.4 FSCQ1565RT 4.4 www.onsemi.com 4 7.0 FSCQ0965RT FSCQ1565RT Continuous Drain Current (TC = 100°C) 3.8 A A(rms) FSCQ Series ABSOLUTE MAXIMUM RATINGS (TA = 25°C unless otherwise specified) (continued) Parameter Single−Pulsed Avalanche Energy (Note 5) FSCQ0765RT Total Power Dissipation (TC = 25°C with Infinite Heat Sink) Symbol Value Unit EAS 570 mJ FSCQ0965RT 630 FSCQ1265RT 950 FSCQ1565RT 1050 FSCQ0765RT PD 45 FSCQ0965RT 49 FSCQ1265RT 50 FSCQ1565RT 75 W Operating Junction Temperature TJ 150 °C Operating Ambient Temperature TA −25 to +85 °C TSTG −55 to +150 °C 2.0 kV 300 V Storage Temperature Range Human Body Model (All Pins Except VFB) (GND − VFB = 1.7 kV) Machine Model (All Pins Except VFB) (GND − VFB = 170 V) ESD Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality should not be assumed, damage may occur and reliability may be affected. 4. Repetitive rating: pulse width limited by maximum junction temperature. 5. L = 15 mH, starting TJ = 25°C. These parameters, although guaranteed by design, are not tested in production. THERMAL CHARACTERISTICS (TA = 25°C unless otherwise specified) Characteristic Junction−to Case Thermal Impedance Characteristic Symbol Value Unit FSCQ0765RT JC 2.60 °C/W FSCQ0965RT 2.55 FSCQ1265RT 2.50 FSCQ1565RT 2.00 www.onsemi.com 5 FSCQ Series ELECTRICAL CHARACTERISTICS (TA = 25°C unless otherwise specified) Symbol Parameter Test Condition Min Typ Max Unit Drain−Source Breakdown Voltage VGS = 0 V, ID = 250 mA 650 − − V Zero Gate Voltage Drain Current VDS = 650 V, VGS = 0 V − − 250 mA FSCQ0765RT VGS = 10 V, ID = 1 A − 1.40 1.60 W FSCQ0965RT VGS = 10 V, ID = 1 A − 1.00 1.20 FSCQ1265RT VGS = 10 V, ID = 1 A − 0.75 0.90 FSCQ1565RT VGS = 10 V, ID = 1 A − 0.53 0.70 FSCQ0765RT VGS = 0 V, VDS = 25 V, f = 1 MHz − 1415 − − 1750 − FSCQ1265RT − 2400 − FSCQ1565RT − 3050 − − 100 − − 130 − FSCQ1265RT − 175 − FSCQ1565RT − 220 − 18 20 22 SENSEFET PART BVDSS IDSS RDS(ON) CISS Drain−Source On−State Resistance Input Capacitance FSCQ0965RT COSS Output Capacitance FSCQ0765RT FSCQ0965RT VGS = 0 V, VDS = 25 V, f = 1 MHz pF pF CONTROL SECTION fOSC DfOSC IFB Switching Frequency VFB = 5 V, VCC = 18 V Switching Frequency Variation (Note 7) Feedback Source Current kHz −25°C ≤ TA ≤ 85°C 0 ±5 ±10 % VFB = 0.8 V, VCC = 18 V 0.50 0.65 0.80 mA DMAX Maximum Duty Cycle VFB = 5 V, VCC = 18 V 92 95 98 % DMIN Minimum Duty Cycle VFB = 0 V, VCC = 18 V − 0 − % VFB = 1 V 14 15 16 V 8 9 10 18 20 22 ms 0.25 0.40 0.55 V VFB = 0 V 60 100 140 mA VFB = 0.9 V, Duty = 50% 1.2 1.4 1.6 ms VFB = 0.9 V → 0 V 1.2 1.4 1.6 ms VCC = 18 V 7.0 7.5 8.0 V VSTART UVLO Threshold Voltage VSTOP tSS Soft−Start Time (Note 6) BURST MODE SECTION VBEN Burst Mode Enable Feedback Voltage IBFB Burst Mode Feedback Source Current tBS Burst Mode Switching Time tBH Burst Mode Hold Time PROTECTION SECTION VSD Shutdown Feedback Voltage IDELAY Shutdown Delay Current VFB = 5 V, VCC = 18 V 4 5 6 mA VOVP Over−Voltage Protection VFB = 3 V 11 12 13 V VOCL Over−Current Latch Voltage (Note 6) VCC = 18 V 0.9 1.0 1.1 V TSD Thermal Shutdown Temperature (Note 7) 140 − − °C 4.2 4.6 5.0 V SYNC SECTION VCC = 18 V, VFB = 5 V VSH1 Sync Threshold in Normal QR (H) VSL1 Sync Threshold in Normal QR (L) 2.3 2.6 2.9 V VSH2 Sync Threshold in Extended QR (H) 2.7 3.0 3.3 V VSL2 Sync Threshold in Extended QR (L) 1.6 1.8 2.0 V fSYH Extended QR Enable Frequency − 90 − kHz fSYL Extended QR Disable Frequency − 45 − kHz www.onsemi.com 6 FSCQ Series ELECTRICAL CHARACTERISTICS (TA = 25°C unless otherwise specified) (continued) Symbol Parameter Test Condition Min Typ Max Unit VFB = 5 V − 4 6 mA FSCQ0965RT − 6 8 FSCQ1265RT − 6 8 FSCQ1565RT − 7 9 − 0.25 0.50 mA TOTAL DEVICE SECTION IOP IOB ISTART ISN Operating Supply Current in Normal Operation (Note 8) FSCQ0765RT Operating Supply Current in Burst Mode (Non−Switching) (Note 8) VFB = GND Startup Current VCC = VSTART − 0.1 V − 25 50 mA Sustain Latch Current (Note 6) VCC = VSTOP − 0.1 V − 50 100 mA VCC = 18 V, VFB = 5 V 4.40 5.00 5.60 A FSCQ0965RT 5.28 6.00 6.72 FSCQ1265RT 6.16 7.00 7.84 FSCQ1565RT 7.04 8.00 8.96 CURRENT SENSE SECTION ILIM IBUR(pk) Maximum Current Limit (Note 9) Burst Peak Current FSCQ0765RT FSCQ0765RT VCC = 18 V, VFB = Pulse 0.65 0.90 1.15 FSCQ0965RT 0.60 0.90 1.20 FSCQ1265RT 0.80 1.20 1.60 FSCQ1565RT − 1.00 − A Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product performance may not be indicated by the Electrical Characteristics if operated under different conditions. 6. These parameters, although guaranteed, are tested only in wafer test process. 7. These parameters, although guaranteed by design, are not tested in production. 8. This parameter is the current flowing in the control IC. 9. These parameters indicate inductor current. 10. These parameters, although guaranteed, are tested only in wafer test process. www.onsemi.com 7 FSCQ Series TYPICAL PERFORMANCE CHARACTERISTICS Figure 4. Operating Supply Current Figure 5. Burst Mode Supply Current (Non−Switching) Figure 7. Start Threshold Voltage Figure 6. Startup Current Figure 8. Stop Threshold Voltage Figure 9. Initial Frequency www.onsemi.com 8 FSCQ Series TYPICAL PERFORMANCE CHARACTERISTICS (continued) Figure 10. Maximum Duty Cycle Figure 11. Over−Voltage Protection Figure 13. Shutdown Feedback Voltage Figure 12. Shutdown Delay Current Figure 14. Feedback Source Current Figure 15. Burst Mode Feedback Source Current www.onsemi.com 9 FSCQ Series TYPICAL PERFORMANCE CHARACTERISTICS (continued) Figure 16. Feedback Offset Voltage Figure 17. Burst Mode Enable Feedback Voltage Figure 18. Sync. Threshold in Normal QR(H) Figure 19. Sync. Threshold in Normal QR(L) Figure 20. Sync. Threshold in Extended QR(H) Figure 21. Sync. Threshold in Extended QR(L) www.onsemi.com 10 FSCQ Series TYPICAL PERFORMANCE CHARACTERISTICS (continued) Figure 23. Extended QR Disable Frequency Figure 22. Extended QR Enable Frequency Figure 24. Pulse−by−Pulse Current Limit www.onsemi.com 11 FSCQ Series Functional Description The minimum average of the current supplied from the AC is given by: Startup Figure 25 shows the typical startup circuit and the transformer auxiliary winding for the FSCQ series. Before the FSCQ series begins switching, it consumes only startup current (typically 25 mA). The current supplied from the AC line charges the external capacitor (Ca1) that is connected to the VCC pin. When VCC reaches the start voltage of 15 V (VSTART), the FSCQ series begins switching and its current consumption increases to IOP. Then, the FSCQ series continues normal switching operation and the power required is supplied from the transformer auxiliary winding, unless VCC drops below the stop voltage of 9 V (VSTOP). To guarantee stable operation of the control IC, VCC has under−voltage lockout (UVLO) with 6 V hysteresis. Figure 26 shows the relationship between the operating supply current of the FSCQ series and the supply voltage (VCC). I SUP AVG + ǒ Ǹ2 @ VAC MIN p − V START 2 Ǔ @ 1 R STR (eq. 1) where Vacmin is the minimum input voltage, VSTART is the FSCQ series’ start voltage (15 V), and Rstr is the startup resistor. The startup resistor should be chosen so that Isupavg is larger than the maximum startup current (50 mA). Once the resistor value is determined, the maximum loss in the startup resistor is obtained as: Loss + 1 R STR ȡǒV @ȧ Ȣ AC Ǔ MAX 2 ) V START 2 2 * 2 Ǹ2 @ V START @ V AC p ȣ ȧ Ȥ MAX (eq. 2) where Vacmax is the maximum input voltage. The startup resistor should have properly rated dissipation wattage. CDC Synchronization The FSCQ series employs a quasi−resonant switching technique to minimize the switching noise and loss. In this technique, a capacitor (Cr) is added between the MOSFET drain and the source, as shown in Figure 27. The basic waveforms of the quasi−resonant converter are shown in Figure 28. The external capacitor lowers the rising slope of the drain voltage to reduce the EMI caused when the MOSFET turns off. 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 28. 1N4007 AC line (Vacmin − Vacmax) Isup Rstr Da VCC FSCQ−Series Ca2 Ca1 CDC Figure 25. Startup Circuit + VDC − Np Ns Lm Drain ICC IOP Value FSCQ0565RT: 4 mA (Typ.) FSCQ0765RT: 4 mA (Typ.) FSCQ0965RT: 6 mA (Typ.) FSCQ1265RT: 6 mA (Typ.) FSCQ1565RT: 7 mA (Typ.) Cr Ids Sync + Vds − GND Vco Vcc Da Rcc IOP Ca1 Power Down Power Up VCC VSTART = 15 V Na DSY RSY1 ISTART VSTOP = 9 V Ca2 CSY VZ Figure 26. Relationship between Operating Supply Current and VCC Voltage RSY2 Figure 27. Synchronization Circuit www.onsemi.com 12 Vo FSCQ Series Vds MOSFET On MOSFET Off Vgs 2VRO tQ VRO VRO Vds Vsync VDC V Vrh (4.6 V) Ids tR Ipk Vrf (2.6 V) MOSFET Gate Figure 28. Quasi−Resonant Operation Waveforms ON The minimum drain voltage is indirectly detected by monitoring the VCC winding voltage, as shown in Figure 27 and Figure 29. Choose voltage dividers, RSY1 and RSY2, so that the peak voltage of the sync signal (Vsypk) is lower than the OVP voltage (12 V) to avoid triggering OVP in normal operation. It is typical to set Vsypk to be lower than OVP voltage by 3–4 V. To detect the optimum time to turn on MOSFET, the sync capacitor (CSY) should be determined so that tR is the same with tQ, as shown in Figure 29. The tR and tQ are given as: t R + R SY2 @ C SY @ In ǒ V CO 2.6 @ R SY2 R SY1 ) R SY2 t Q + p @ ǸL m @ C eo V CO + where: Lm Ns Na VFo VFa Ceo N a @ ǒV O ) V FOǓ Ns * V Fa Ǔ ON Figure 29. Normal QR Operation Waveforms Switching Frequency Extended QR Operation 90 kHz Normal QR Operation (eq. 3) (eq. 4) (eq. 5) Output Power Figure 30. Extended Quasi−Resonant Operation is the primary side inductance of the transformer, is the number of turns for the output winding, is the number of turns for the VCC winding, is the diode forward−voltage drop of the output winding, is the diode forward−voltage drop of the VCC winding; and is the sum of the output capacitance of the MOSFET and the external capacitor, Cr. In general, the QRC has a limitation in a wide load range application, since the switching frequency increases as the output load decreases, resulting in a severe switching loss in the light load condition. To overcome this limitation, the FSCQ series employs an extended quasi−resonant switching operation. Figure 30 shows the mode change between normal and extended quasi−resonant operations. In the normal quasi−resonant operation, the FSCQ series enters into the extended quasi−resonant operation when the switching frequency exceeds 90 kHz as the load reduces. To reduce the switching frequency, the MOSFET is turned on when the drain voltage reaches the second minimum level, www.onsemi.com 13 FSCQ Series as shown in Figure 31. Once the FSCQ series enters into the extended quasi−resonant operation, the first sync signal is ignored. After the first sync signal is applied, the sync threshold levels are changed from 4.6 V and 2.6 V to 3 V and 1.8 V, respectively, and the MOSFET turn−on time is synchronized to the second sync signal. The FSCQ series returns to its normal quasi−resonant operation when the switching frequency reaches 45 kHz as the load increases. Leading Edge Blanking (LEB) At the instant the internal SENSEFET is turned on, there is usually a high current spike through the SENSEFET, caused by the external resonant capacitor across the MOSFET and secondary−side rectifier reverse recovery. Excessive voltage across the Rsense resistor can lead to incorrect feedback operation in the current mode PWM control. To counter this effect, the FSCQ series employs a leading edge blanking (LEB) circuit. This circuit inhibits the PWM comparator for a short time (tLEB) after the Sense FET is turned on. Vds 2VRO VCC Vref Idelay Vfb VO Vsyn c 4 H11A817A D1 CB D2 + Vfb * 4.6 V 3V 2.6 V KA431 OSC 2.5R Gate Driver R − 1.8 V VSD MOSFET Gate ON IFB OLP Rsense Figure 32. Pulse Width Modulation (PWM) Circuit ON Protection Circuits Figure 31. Extended QR Operation Waveforms The FSCQ series has several self−protective functions such as overload protection (OLP), abnormal over−current protection (AOCP), overvoltage protection (OVP), and thermal shutdown (TSD). OLP and OVP are auto−restart mode protections, while TSD and AOCP are latch mode protections. Because these protection circuits are fully integrated into the IC without external components, the reliability can be improved without increasing cost. − Auto− Restart Mode Protection: Once the fault condition is detected, switching is terminated and the SENSEFET remains off. This causes VCC to fall. When VCC falls to the under voltage lockout (UVLO) stop voltage of 9 V, the protection is reset and the FSCQ series consumes only startup current (25 mA). Then, the VCC capacitor is charged up, since the current supplied through the startup resistor is larger than the current that the FPS consumes. When VCC reaches the start voltage of 15 V, the FSCQ series resumes its 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 (see Figure 33). − Latch Mode Protection: Once this protection is triggered, switching is terminated and the SENSEFET remains off until the AC power line is unplugged. Then, VCC continues charging and discharging between 9 V and 15 V. The latch is reset only when VCC is discharged to 6 V by unplugging the AC power line. Feedback Control The FSCQ series employs current mode control, as shown in Figure 32. An optocoupler (such as onsemi’s H11A817A) and shunt regulator (such as onsemi’s KA431) are typically used to implement the feedback network. Comparing the feedback voltage with the voltage across the Rsense resistor, plus an offset voltage, makes it possible to control the switching duty cycle. When the reference pin voltage of the shunt regulator exceeds the internal reference voltage of 2.5 V, the opto−coupler LED current increases, pulling down the feedback voltage and reducing the duty cycle. This typically occurs when input voltage is increased or output load is decreased. Pulse−by−Pulse Current Limit Because current mode control is employed, the peak current through the SENSEFET is limited by the inverting input of the PWM comparator (Vfb*) as shown in Figure 32. The feedback current (IFB) and internal resistors are designed so that the maximum cathode voltage of diode D2 is about 2.8 V, which occurs when all IFB flows through the internal resistors. Since D1 is blocked when the feedback voltage (Vfb) exceeds 2.8 V, 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. www.onsemi.com 14 FSCQ Series Fault occurs Power on Vds 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 FSCQ series has OLP (Overload Protection), it is not enough to protect the FSCQ series in that abnormal case, since severe current stress will be imposed on the SENSEFET until the OLP triggers. The FSCQ series has an internal AOCP (Abnormal Over−Current Protection) circuit as shown in Figure 35. 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 then 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 SMPS. This protection is implemented in the latch mode. Fault removed Vcc 15 V 9V ICC IOP ISTART Normal Fault operation situation t Normal operation Figure 33. Auto Restart Mode Protection 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 over load protection circuit can be triggered during the load transition. To avoid this undesired operation, the overload protection circuit is designed to trigger after a specified time to determine whether it is a transient situation or an 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 opto−coupler LED, which also reduces the opto−coupler transistor current, thus increasing the feedback voltage (Vfb). If Vfb exceeds 2.8 V, D1 is blocked, and the 5 mA current source starts to charge CB slowly up to VCC. In this condition, Vfb continues increasing until it reaches 7.5 V, then the switching operation is terminated as shown in Figure 34. The delay for shutdown is the time required to charge CB from 2.8 V to 7.5 V with 5 mA. In general, a 20~50 ms delay is typical for most applications. OLP is implemented in auto restart mode. PWM R Q R Q Gate Driver LEB 2 AOCP GND VAOCP − Figure 35. AOCP Block Over−Voltage Protection (OVP) If the secondary side feedback circuit malfunctions or a solder defect causes an open in the feedback path, the current through the opto−coupler transistor becomes almost zero. Then, Vfb climbs up in a similar manner to the over load situation, forcing the preset maximum current to be supplied to the SMPS until the over load 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. In order to prevent this situation, an over voltage protection (OVP) circuit is employed. In general, the peak voltage of the sync signal is proportional to the output voltage and the FSCQ series uses a sync signal instead of directly monitoring the output voltage. If the sync signal exceeds 12 V, an OVP is triggered resulting in a shutdown of SMPS. In order to avoid undesired triggering of OVP during normal operation, the peak voltage of the sync signal should be designed to be below 12 V. This protection is implemented in the auto restart mode. 2.8 V t12 = CB*(7.5 − 2.8)/Idelay t S R Overload Protection t1 OSC + VFB 7.5 V 2.5R t Figure 34. Overload Protection www.onsemi.com 15 FSCQ Series Figure 38 shows the burst mode operation waveforms. When the picture ON signal is disabled, Q1 is turned off and R3 and Dz are connected to the reference pin of KA431 through D1. Before Vo2 drops to Vo2stby, the voltage on the reference pin of KA431 is higher than 2.5 V, which increases the current through the opto LED. This pulls down the feedback voltage (VFB) of FSCQ series and forces FSCQ series to stop switching. If the switching is disabled longer than 1.4 ms, FSCQ series enters into burst operation and the operating current is reduced from IOP to 0.25 mA (IOB). Since there is no switching, Vo2 decreases until it reaches Vo2stby. As Vo2 reaches Vo2stby, the current through the opto LED decreases allowing the feedback voltage to rise. When the feedback voltage reaches 0.4 V, FSCQ series resumes switching with a predetermined peak drain current of 0.9 A. After burst switching for 1.4 ms, FSCQ series stops switching and checks the feedback voltage. If the feedback voltage is below 0.4 V, FSCQ series stops switching until the feedback voltage increases to 0.4 V. If the feedback voltage is above 0.4 V, FSCQ series goes back to the normal operation. The output voltage drop circuit can be implemented alternatively, as shown in Figure 37. In the circuit, the FSCQ series goes into burst mode, when picture off signal is applied to Q1. Then, Vo2 is determined by the Zener diode breakdown voltage. Assuming that the forward voltage drop of opto LED is 1 V, the approximate value of Vo2 in standby mode is given by: Thermal Shutdown (TSD) The SENSEFET and the control IC are built in one package. This makes it easy for the control IC to detect abnormal over temperature of the SENSEFET. When the temperature exceeds approximately 150°C, the thermal shutdown triggers. This protection is implemented in the latch mode. Soft Start The FSCQ series has an internal soft−start circuit that increases PWM comparator’s inverting input voltage together with the SENSEFET current slowly after it starts up. The typical soft start time is 20 ms. The pulse width to the power switching device is progressively increased to establish the correct working conditions for transformers, inductors, and capacitors. Increasing the pulse width to the power switching device also helps prevent transformer saturation and reduces the stress on the secondary diode during startup. For a fast build up of the output voltage, an offset is introduced in the soft−start reference current. Burst Operation To minimize the power consumption in the standby mode, the FSCQ series employs burst operation. Once FSCQ series enters burst mode, FSCQ series allows all output voltages and effective switching frequency to be reduced. Figure 36 shows the typical feedback circuit for C−TV applications. In normal operation, the picture on signal is applied and the transistor Q1 is turned on, which decouples R3, DZ and D1 from the feedback network. Therefore, only VO1 is regulated by the feedback circuit in normal operation and determined by R1 and R2 as: V O1 NORM + 2.5 @ ǒ R1 ) R2 R2 Ǔ V O2 STBY + V Z ) 0.7 ) 2.5 Linear Regulator (eq. 6) RD CF C KA431 A (eq. 7) RD RF R1 R R2 Linear Regulator R1 CF Micom Q1 Picture OFF Dz Rbias A Micom Dz VO1 (B+) KA431 (eq. 8) VO1 (B+) Rbias VO2 C + VZ ) 1 VO2 In standby mode, the picture ON signal is disabled and the transistor Q1 is turned off, which couples R3, DZ, and D1 to the reference pin of KA431. Then, VO2 is determined by the Zener diode breakdown voltage. Assuming that the forward voltage drop of D1 is 0.7 V, VO2 in standby mode is approximately given by: V O2 STBY RF D1 R3 Figure 37. Feedback Circuit to Drop Output Voltage in Standby Mode Q1 Picture ON R R2 Figure 36. Typical Feedback Circuit to Drop Output Voltage in Standby Mode www.onsemi.com 16 FSCQ Series (a) (b) (c) norm Vo2 Vo2 stby VFB 0.4 V Iop IOP IOB Vds Picture On Picture On Picture Off Burst Mode 0.4 V 0.3 V VFB 0.4 V 0.4 V Vds 1.4 ms Ids 1.4 ms 0.9 A 0.9 A (a) Mode Change to Burst Operation (b) Burst Operation (c) Mode Change to Normal Operation Figure 38. Burst Operation Waveforms www.onsemi.com 17 FSCQ Series FSCQ0765RT Typical Application Circuit FSCQ0765RT TYPICAL APPLICATION CIRCUIT Application Output Power Input Voltage Output Voltage (Max. Current) C−TV 83 W Universal Input (90−270 Vac) 12 V (1 A) 18 V (0.5 A) 125 V (0.4 A) 24 V (0.5 A) • Enhanced System Reliability Through Various Features • High Efficiency (>83% at 90 Vac Input) • Wider Load Range through the Extended • • • Quasi−Resonant Operation Low Standby Mode Power Consumption (83% at 90 Vac Input) • Wider Load Range through the Extended • • • Quasi−Resonant Operation Low Standby Mode Power Consumption (