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FSCQ - Green Mode Fairchild Power Switch (FPS™) - Fairchild Semiconductor

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FSCQ
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FAIRCHILD[FairchildSemiconductor]
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http://www.fairchildsemi.com/
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FSCQ - Green Mode Fairchild Power Switch (FPS™) - Fairchild Semiconductor
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FSCQ-Series Green Mode Fairchild Power Switch (FPS™) February 2006 FSCQ-Series FSCQ0565RT/FSCQ0765RT/FSCQ0965RT/FSCQ1265RT/ FSCQ1465RT/FSCQ1565RT/FSCQ1565RP Green Mode Fairchild Power Switch (FPS™) Features ■ Optimized for Quasi-Resonant Converter (QRC) ■ Advanced Burst-Mode Operation for under 1W Description A Quasi-Resonant Converter (QRC) typically shows lower EMI and higher power conversion efficiency compared to 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, and is specifically designed for quasiresonant 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 a 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 simultaneously increasing efficiency, productivity, and system reliability. These devices provide a basic platform that is well suited for cost-effective designs of quasi-resonant switching flyback converters. Standby Power Consumption ■ Pulse-by-Pulse Current Limit ■ Over Load Protection (OLP) – Auto Restart ■ Over Voltage Protection (OVP) – Auto Restart ■ Abnormal Over Current Protection (AOCP) – Latch ■ Internal Thermal Shutdown (TSD) – Latch ■ Under Voltage Lock Out (UVLO) with Hysteresis ■ Low Startup Current (typical: 25µA) ■ Internal High Voltage SenseFET ■ Built-in Soft Start (20ms) ■ Extended Quasi-Resonant Switching Applications ■ CTV ■ Audio Amplifier Related Application Notes ■ AN4146: Design Guidelines for Quasi-Resonant Converters Using FSCQ-Series Fairchild Power Switch. ■ AN4140: Transformer Design Consideration for Off-Line Flyback Converters Using Fairchild Power Switch. Ordering Information Product Number FSCQ0565RTYDTU FSCQ0765RTYDTU FSCQ0965RTYDTU FSCQ1265RTYDTU FSCQ1465RTYDTU FSCQ1565RTYDTU FSCQ1565RPVDTU YDTU: Forming Type VDTU: Forming Type Package TO-220F-5L (Forming) TO-220F-5L (Forming) TO-220F-5L (Forming) TO-220F-5L (Forming) TO-220F-5L( Forming) TO-220F-5L (Forming) TO-3PF-7L (Forming) Marking Code CQ0565RT CQ0765RT CQ0965RT CQ1265RT CQ1465RT CQ1565RT CQ1565RP BVdss 650V 650V 650V 650V 650V 650V 650V Rds(ON) Max. 2.2Ω 1.6Ω 1.2Ω 0.9Ω 0.8Ω 0.7Ω 0.7Ω ©2006 Fairchild Semiconductor Corporation 1 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) Typical Circuit VO AC IN Drain FSCQ-Series PWM Sync VFB GND VCC Figure 1. Typical Flyback Application Table 1. Maximum Output Power Output Power Table3 230 VAC ±15%2 Product FSCQ0565RT FSCQ0765RT FSCQ0965RT FSCQ1265RT FSCQ1465RT FSCQ1565RT FSCQ1565RP 85–265 VAC Open Frame1 60W 85W 110W 140W 160W 170W 210W Open Frame1 70W 100W 130W 170W 190W 210W 250W Notes: 1. Maximum practical continuous power in an open frame design at 50°C ambient. 2. 230 VAC or 100/115 VAC with doubler. 3. The junction temperature can limit the maximum output power. 2 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) Internal Block Diagram Sync 5 + Threshold Vcc 3 Quasi-Resonant (QR) Switching Controller fs + 9V/15V Drain 1 - Soft Start 4.6V/2.6V: Normal QR 3.0V/1.8V: Extended QR Burst Mode Controller VCC good Auxiliary Vref Normal Operation VBurst OSC Main Bias Normal Operation Vref I BFB VCC Idelay Vref I FB Burst Switching Vref IB PWM S Q Q Internal Bias VFB 4 2.5R R R Gate Driver LEB 600ns VSD Sync Vovp VCC good (VCC = 9V) S R Q Q Q Q S R AOCP 2 GND TSD Vocp Power Off Reset (VCC = 6V) Figure 2. Functional Block Diagram of FSCQ-Series 3 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) Pin Configuration TO-220F-5L 5. Sync 4. Vfb 3. Vcc 2. GND 1. Drain TO-3PF-7L 5. Sync 4. Vfb 3. Vcc 2. GND 1. Drain Figure 3. Pin Configuration (Top View) Pin Definitions Pin Number 1 2 3 4 Pin Name Drain GND Vcc Vfb Pin Function Description High voltage power SenseFET drain connection. This pin is the control ground and the SenseFET source. This pin is the positive supply input. This pin provides internal operating current for both start-up and steady-state operation. This pin is internally connected to the inverting input of the PWM comparator. The collector of an optocoupler 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 7.5V, the over load protection triggers, which results in the FPS shutting down. 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 4.6V/2.6V. Whereas, the sync threshold is changed to 3.0V/1.8V in an extended quasi-resonant operation. 5 Sync 4 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) Absolute Maximum Ratings (TA = 25°C, unless otherwise specified) Parameter Drain Pin Voltage Supply Voltage Analog Input Voltage Range Drain Current Pulsed4 IDM Symbol VDS VCC Vsync VFB FSCQ0565RT FSCQ0765RT FSCQ0965RT FSCQ1265RT FSCQ1465RT FSCQ1565RT FSCQ1565RP Value 650 20 -0.3 to 13V -0.3 to VCC 11.2 15.2 16.4 21.2 22 26.4 33.2 2.8 3.8 4.1 5.3 5.5 6.6 8.3 5 7 7.6 11 12 13.3 15 1.7 2.4 2.6 3.4 3.5 4.4 5.5 400 570 630 950 1000 1050 1050 Unit V V V V A Continuous Drain Current (Tc = 25°C) (Tc: Case Back Surface Temperature) ID FSCQ0565RT FSCQ0765RT FSCQ0965RT FSCQ1265RT FSCQ1465RT FSCQ1565RT FSCQ1565RP A(rms) Continuous Drain Current* (TDL = 25°C) (TDL:Drain Lead Temperature) ID* FSCQ0565RT FSCQ0765RT FSCQ0965RT FSCQ1265RT FSCQ1465RT FSCQ1565RT FSCQ1565RP A(rms) Continuous Drain Current (TC = 100°C) ID FSCQ0565RT FSCQ0765RT FSCQ0965RT FSCQ1265RT FSCQ1465RT FSCQ1565RT FSCQ1565RP A(rms) Single-Pulsed Avalanche Energy5 EAS FSCQ0565RT FSCQ0765RT FSCQ0965RT FSCQ1265RT FSCQ1465RT FSCQ1565RT FSCQ1565RP mJ 5 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) Absolute Maximum Ratings (Continued) (TA = 25°C, unless otherwise specified) Total Power Dissipation (Tc = 25°C with Infinite Heat Sink) PD FSCQ0565RT FSCQ0765RT FSCQ0965RT FSCQ1265RT FSCQ1465RT FSCQ1565RT FSCQ1565RP Operating Junction Temperature Operating Ambient Temperature Storage Temperature Range ESD Capability, HBM Model (All pins except Vfb) ESD Capability, Machine Model (All pins except Vfb) TJ TA TSTG – – 38 45 49 50 60 75 98 +150 -25 to +85 -55 to +150 2.0 (GND – Vfb = 1.7kV) 300 (GND – Vfb = 170V) °C °C °C kV V W Notes: 4. Repetitive rating: pulse width limited by maximum junction temperature. 5. L = 15mH, starting Tj = 25°C, These parameters, although guaranteed at the design, are not tested in mass production. Thermal Impedance (TA = 25°C unless otherwise specified) Parameter Junction to Case Thermal Impedance θJC Symbol FSCQ0565RT FSCQ0765RT FSCQ0965RT FSCQ1265RT FSCQ1465RT FSCQ1565RT FSCQ1565RP Value 3.29 2.60 2.55 2.50 2.10 2.00 1.28 Unit °C/W 6 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) Electrical Characteristics (SenseFET Part) (TA = 25°C unless otherwise specified) Parameter Drain-Source Breakdown Voltage BVDSS Zero Gate Voltage Drain Current Drain-Source ON-State Resistance IDSS RDS(ON) FSCQ0565RT FSCQ0765RT FSCQ0965RT FSCQ1265RT FSCQ1465RT FSCQ1565RT FSCQ1565RP Input Capacitance CISS FSCQ0565RT FSCQ0765RT FSCQ0965RT FSCQ1265RT FSCQ1465RT FSCQ1565RT FSCQ1565RP Output Capacitance COSS FSCQ0565RT FSCQ0765RT FSCQ0965RT FSCQ1265RT FSCQ1465RT FSCQ1565RT FSCQ1565RP VGS = 0V, VDS = 25V, f = 1MHz Symbol Condition VGS = 0V, ID = 250µA VDS = 650V,VGS = 0V VGS = 10V, ID = 1A VGS = 10V, ID = 1A VGS = 10V, ID = 1A VGS = 10V, ID = 1A VGS = 10V, ID = 1A VGS = 10V, ID = 1A VGS = 10V, ID = 1A VGS = 0V, VDS = 25V, f = 1MHz Min. Typ. Max. 650 – – – – – – – – – – – – – – – – – – – – – – – – 1.76 1.4 1.0 0.75 0.7 0.53 0.53 1080 1415 1750 2400 2400 3050 3050 90 100 130 175 185 220 220 – 250 2.2 1.6 1.2 0.9 0.8 0.7 0.7 – – – – – – – – – – – – – – Unit V µA Ω pF pF 7 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) Electrical Characteristics (Continued) (TA = 25°C unless otherwise specified) Parameter Control Section Switching Frequency Switching Frequency Variation7 Feedback Source Current Maximum Duty Cycle Minimum Duty Cycle UVLO Threshold Voltage Soft Start Time6 FOSC ∆FOSC IFB DMAX DMIN VSTART VSTOP TSS VBEN IBFB TBS TBH VSD IDELAY VOVP VOCL TSD VFB = 0V VFB = 0.9V, Duty = 50% VFB = 0.9V → 0V VCC = 18V VFB = 5V, VCC = 18V VFB = 3V VCC = 18V Burst Mode Section Burst Mode Enable Feedback Voltage Burst Mode Feedback Source Current Burst Mode Switching Time Burst Mode Hold Time Protection Section Shutdown Feedback Voltage Shutdown Delay Current Over Voltage Protection Over Current Thermal Latch Voltage6 Shutdown Temp7 7.0 4 11 0.9 140 7.5 5 12 1.0 – 8.0 6 13 1.1 – V µA V V °C 0.25 60 1.2 1.2 0.40 100 1.4 1.4 0.55 140 1.6 1.6 V µA ms ms VFB = 5V, VCC = 18V -25°C ≤ TA ≤ 85°C VFB = 0.8V, VCC = 18V VFB = 5V, VCC = 18V VFB = 0V, VCC = 18V VFB = 1V 18 0 0.5 92 – 14 8 18 20 ±5 0.65 95 0 15 9 20 22 ±10 0.8 98 – 16 10 22 ms kHz % mA % % V Symbol Condition Min. Typ. Max. Unit Notes: 6. These parameters, although guaranteed, are tested only in EDS (wafer test) process. 7. These parameters, although guaranteed at the design, are not tested in mass production. 8 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) Electrical Characteristics (Continued) (TA = 25°C unless otherwise specified) Parameter Sync Section Sync Threshold in Normal QR (H) Sync Threshold in Normal QR (L) VSH1 VSL1 VCC = 18V, VFB = 5V 4.2 2.3 2.7 1.6 – – 4.6 2.6 3.0 1.8 90 45 5.0 2.9 3.3 2.0 – – V V V V kHz kHz Symbol Condition Min. Typ. Max. Unit Sync Threshold in Extended QR (H) VSH2 Sync Threshold in Extended QR (L) VSL2 Extended QR Enable Frequency Extended QR Disable Frequency Total Device Section Operating Supply Current9 - In Normal Operation IOP FSCQ0565RT VFB = 5V FSCQ0765RT FSCQ0965RT FSCQ1265RT FSCQ1465RT FSCQ1565RT FSCQ1565RP - In Burst Mode (Non-switching) Startup Current Sustain Latch Current11 Current Sense Section Maximum Current Limit10 ILIM FSCQ0565RT VCC = 18V, VFB = 5V FSCQ0765RT FSCQ0965RT FSCQ1265RT FSCQ1465RT FSCQ1565RT FSCQ1565RP Burst Peak Current IBUR(pk) FSCQ0565RT VCC = 18V, VFB = Pulse FSCQ0765RT FSCQ0965RT FSCQ1265RT FSCQ1465RT FSCQ1565RT FSCQ1565RP Notes: 9. This parameter is the current flowing in the control IC. 10. These parameters indicate inductor current. 11. These parameters, although guaranteed, are tested only in EDS (wafer test) process. FSYH FSYL – – – – – – – 4 4 6 6 7 7 7 0.25 25 50 3.5 5 6.0 7 8.0 8 0.65 0.9 0.9 1.2 0.9 1 1 6 6 8 8 9 9 9 0.50 50 100 3.92 5.6 6.72 7.84 8.96 8.96 0.85 1.15 1.2 1.6 1.2 – – mA IOB ISTART ISN VFB = GND VCC = VSTART – 0.1V VCC = VSTOP – 0.1V – – – 3.08 4.4 5.28 6.16 7.04 7.04 0.45 0.65 0.6 0.8 0.6 – – mA µA µA A 10.12 11.5 12.88 A 9 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) Electrical Characteristics Operating Supply Current 1.2 Normalized to 25°C Normalized to 25°C 0 50 Temp (°C) 100 150 Burst-mode Supply Current (Non-Switching) 1.4 1.2 1.0 0.8 0.6 -50 1.0 0.8 -50 0 50 Temp (°C) 100 150 Start-Up Current 1.4 Normalized to 25°C Normalized to 25°C 1.2 1.0 0.8 0.6 -50 1.10 1.05 1.00 0.95 0.90 -50 Start Threshold Voltage 0 50 Temp (°C) 100 150 0 50 Temp (°C) 100 150 Stop Threshold Voltage 1.10 Normalized to 25°C Normalized to 25°C 1.05 1.00 0.95 0.90 -50 1.10 1.05 1.00 0.95 0.90 -50 Initial Frequency 0 50 Temp (°C) 100 150 0 50 Temp (°C) 100 150 10 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) Electrical Characteristics (Continued) Maximum Duty Cycle 1.10 Normalized to 25°C 1.05 1.00 0.95 0.90 -50 Normalized to 25°C 1.10 1.05 1.00 0.95 0.90 -50 Over Voltage Protection 0 50 Temp (°C) 100 150 0 50 Temp (°C) 100 150 Shutdown Delay Current 1.2 Normalized to 25°C 1.1 1.0 0.9 0.8 -50 Normalized to 25°C 1.10 1.05 1.00 0.95 0.90 -50 Shutdown Feedback Voltage 0 50 Temp (°C) 100 150 0 50 Temp (°C) 100 150 Feedback Source Current 1.2 Normalized to 25°C Normalized to 25°C 1.1 1.0 0.9 0.8 -50 1.2 1.1 1.0 0.9 Burst Mode Feedback Source Current 0 50 Temp (°C) 100 150 0.8 -50 0 50 Temp (°C) 100 150 11 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) Electrical Characteristics (Continued) Feedback Offset Voltage 1.4 Normalized to 25°C 1.2 1.0 0.8 0.6 -50 Normalized to 25°C 1.4 1.2 1.0 0.8 0.6 -50 Burst Mode Enable Feedback Voltage 0 50 Temp (°C) 100 150 0 50 Temp (°C) 100 150 Sync. Threshold in Normal QR(H) 1.10 Normalized to 25°C 1.05 1.00 0.95 0.90 -50 Normalized to 25°C 1.10 1.05 1.00 0.95 0.90 -50 Sync. Threshold in Normal QR(L) 0 50 Temp (°C) 100 150 0 50 Temp (°C) 100 150 Sync. Threshold in Extended QR(H) 1.10 Normalized to 25°C 1.05 1.00 0.95 0.90 -50 Normalized to 25°C 1.10 1.05 1.00 0.95 0.90 -50 Sync. Threshold in Extended QR(L) 0 50 Temp (°C) 100 150 0 50 Temp (°C) 100 150 12 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) Electrical Characteristics (Continued) Extended QR Enable Frequency 1.10 Normalized to 25°C 1.05 1.00 0.95 0.90 -50 Normalized to 25°C 1.10 1.05 1.00 0.95 0.90 -50 Extended QR Disable Frequency 0 50 Temp (°C) 100 150 0 50 Temp (°C) 100 150 Pulse-by-pulse Current Limit 1.10 Normalized to 25°C 1.05 1.00 0.95 0.90 -50 0 50 Temp (°C) 100 150 13 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) Functional Description 1. Startup: Figure 4 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 25µA). 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 15V (VSTART), the FSCQSeries begins switching, and its current consumption increases to IOP. Then, the FSCQ-Series continues its normal switching operation and the power required for the FSCQ-Series is supplied from the transformer auxiliary winding, unless VCC drops below the stop voltage of 9V (VSTOP). To guarantee the stable operation of the control IC, VCC has under voltage lockout (UVLO) with 6V hysteresis. Figure 5 shows the relationship between the operating supply current of the FSCQ-Series and the supply voltage (VCC). The minimum average of the current supplied from the AC is given by: avg I sup V start  2 ⋅ V ac 1 =  ---------------------------- – -------------  • --------π 2  R str  min where Vacmin is the minimum input voltage, Vstart is the FSCQ-Series start voltage (15V), and Rstr is the startup resistor. The startup resistor should be chosen so that Isupavg is larger than the maximum startup current (50µA). Once the resistor value is determined, the maximum loss in the startup resistor is obtained as: max ( Vacmax ) 2 + Vstart2 2 2 • Vstart • Vac 1 Loss = --------- •  ---------------------------------------------- – ----------------------------------------------------   R str  2 π where Vacmax is the maximum input voltage. The startup resistor should have properly-rated dissipation wattage. 2. Synchronization: The FSCQ-Series employs a quasiresonant 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 6. The basic waveforms of the quasiresonant converter are shown in Figure 7. 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 7. CDC 1N4007 AC line (Vacmin – Vacmax) Rstr VCC FSCQ-Series Ca1 Ca2 Da Isup + CDC Np Ns Lm Drain Vo VDC – Figure 4. Startup circuit Sync ICC IOP Value FSCQ0565RT : 4mA (Typ.) FSCQ0765RT : 4mA (Typ.) FSCQ0965RT : 6mA (Typ.) FSCQ1265RT : 6mA (Typ.) FSCQ1465RT : 7mA (Typ.) FSCQ1565RT : 7mA (Typ.) FSCQ1565RP : 7mA (Typ.) Cr + Ids Vds – GND VCC Ca1 VCO RCC Ca2 Da Na DSY IOP RSY1 Power Down Power Up CSY ISTART Vstop = 9V Vstart = 15V Vz VCC RSY2 Figure 5. Relationship Between Operating Supply Current and Vcc Voltage Figure 6. Synchronization Circuit 14 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) MOSFET Off Vgs MOSFET On Vds 2VRO VRO Vds VRO VDC Vsync TQ Vsypk Vrh (4.6V) Vrf (2.6V) Ids Ipk MOSFET Gate TR Figure 7. Quasi-Resonant Operation Waveforms The minimum drain voltage is indirectly detected by monitoring the Vcc winding voltage as shown in Figure 6 and 8. Choose voltage dividers, RSY1 and RSY2, so that the peak voltage of the sync signal (Vsypk) is lower than the OVP voltage (12V) to avoid triggering OVP in normal operation. It is typical to set Vsypk to be lower than OVP voltage by 3–4V. 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 8. The TR and TQ are given as, respectively: R SY2 V co T R = R SY2 • C SY • In  -------- • ---------------------------------   2.6 R SY1 + R SY2 T Q = π ⋅ L m • C eo N a • ( V o + V FO ) V co = ----------------------------------------- – V Fa Ns where Lm is the primary side inductance of the transformer, and Ns and Na are the number of turns for the output winding and VCC winding, respectively, VFo and VFa are the diode forward voltage drops of the output winding and Vcc winding, respectively, and Ceo is the sum of the output capacitance of the MOSFET and the external capacitor, Cr. ON ON Figure 8. Normal Quasi-Resonant Operation Waveforms Switching frequency Extended QR operation 90kHz Normal QR operation 45kHz Output power Figure 9. Extended Quasi-Resonant Operation 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 quasiresonant switching operation. Figure 9 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 90kHz as the load reduces. To reduce the switching frequency, the MOSFET is turned on when the drain voltage 15 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) reaches the second minimum level, as shown in Figure 10. 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 4.6V and 2.6V to 3V and 1.8V, 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 45kHz as the load increases. Vds 2VRO of D2 is clamped at this voltage, thus clamping Vfb*. Therefore, the peak value of the current through the SenseFET is limited. 3.2 Leading Edge Blanking (LEB): At the instant the internal Sense FET is turned on, there is usually a high current spike through the Sense FET, 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. Vcc Vref Idelay Vo Vfb H11A817A IFB OSC SenseFET Vsync 4 CB + Vfb* R - D1 D2 2.5R Gate Driver 4.6V 3V 2.6V 1.8V KA431 VSD MOSFET Gate OLP Rsense ON ON Figure 11. Pulse Width Modulation (PWM) Circuit 4. Protection Circuits: The FSCQ-Series has several self-protective functions such as over load protection (OLP), abnormal over current protection (AOCP), over voltage 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 9V, the protection is reset and the FSCQ-Series consumes only startup current (25µA). 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 15V, 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 12). Figure 10. Extended Quasi-Resonant Operation Waveforms 3. Feedback Control: The FSCQ-Series employs current mode control, as shown in Figure 11. An optocoupler (such as Fairchild’s H11A817A) and shunt regulator (such as Fairchild’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 KA431 exceeds the internal reference voltage of 2.5V, the H11A817A LED current increases, 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. 3.1 Pulse-by-Pulse Current Limit: Because current mode control is employed, the peak current through the SenseFET is limited by the inverting input of the PWM comparator (Vfb*) as shown in Figure 11. The feedback current (IFB) and internal resistors are designed so that the maximum cathode voltage of diode D2 is about 2.8V, which occurs when all IFB flows through the internal resistors. Since D1 is blocked when the feedback voltage (Vfb) exceeds 2.8V, the maximum voltage of the cathode 16 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) – Latch mode protection: Once this protection is triggered, switching is terminated and the Sense FET remains off until the AC power line is unplugged. Then, VCC continues charging and discharging between 9V and 15V. The latch is reset only when VCC is discharged to 6V by unplugging the AC power line. Fault occurs VFB 7.5V Over load protection Vds Power on Fault removed 2.8V T12 = CB * (7.5 – 2.8) / Idelay T1 VCC 15V 9V T2 t Figure 13. Over Load 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 FSCQ-Series has OLP (Over Load 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 14. 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. ICC IOP ISTART t Normal operation Fault situation Normal operation Figure 12. Auto Restart Mode Protection 4.1 Over Load 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 over load 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 optocoupler LED, which also reduces the optocoupler 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 7.5V, then the switching operation is terminated as shown in Figure 13. The delay time for shutdown is the time required to charge CB from 2.8V to 7.5V with 5µA. In general, a 20~50ms delay time is typical for most applications. OLP is implemented in auto restart mode. 2.5R OSC PWM SQ RQ R AOCP – Vaocp Figure 14. AOCP Block 4.3 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 optocoupler 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 17 FSCQ-Series Rev. 1.1.2 + + LEB Rsense 2 GND www.fairchildsemi.com – Gate Driver FSCQ-Series Green Mode Fairchild Power Switch (FPS™) output, the output voltage may exceed the rated voltage before the over load 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 12V, 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 12V. This protection is implemented in the auto restart mode. 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 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. 5. 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 20ms. 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. 6. Burst Operation: In order to minimize the power consumption in the standby mode, the FSCQ-Series employs burst operation. Once FSCQ-Series enters into the burst mode, FSCQ-Series allows all output voltages and effective switching frequency to be reduced. Figure 15 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: R1 + R2 V o1norm = 2.5 •  -------------------   R2  In the 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 0.7V, Vo2 in standby mode is approximately given by: V o2stby = V Z + 0.7 + 2.5 VO2 Linear Regulator VO1 (B +) RD Rbias R1 CF C KA431 A R R2 RF D1 Q1 Picture ON R3 DZ Micom Figure 15. Typical Feedback Circuit to Drop Output Voltage in Standby Mode Figure 17 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 2.5V, 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 1.4ms, FSCQ-Series enters into burst operation and the operating current is reduced from IOP to 0.25mA (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 0.4V, FSCQ-Series resumes switching with a predetermined peak drain current of 0.9A. After burst switching for 1.4ms, FSCQ-Series stops switching and checks the feedback voltage. If the feedback voltage is below 0.4V, FSCQ-Series stops switching until the feedback voltage increases to 0.4V. If the feedback voltage is above 0.4V, FSCQ-Series goes back to the normal operation. The output voltage drop circuit can be implemented alternatively as shown in Figure 16. In the circuit of Figure 16, 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 1V, the approximate value of Vo2 in standby mode is given by: V o2stby = V Z + 1 18 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) VO2 Linear Regulator RD Rbias VO1 (B+) R1 Micom CF C KA431 A DZ RF R R2 Q1 Picture OFF Figure 16. Feedback Circuit to Drop Output Voltage in Standby Mode 19 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) (a) Vo2norm (b) (c) Vo2stby VFB 0.4V IOP IOP IOB Vds Picture On Picture Off Burst Mode Picture On VFB 0.4V 0.3V 0.4V 0.4V Vds 1.4ms Ids 0.9A 0.9A 1.4ms 1.4ms (a) Mode Change to Burst Operation (b) Burst Operation (c) Mode Change to Normal Operation Figure 17. Burst Operation Waveforms 20 www.fairchildsemi.com FSCQ-Series Rev. 1.1.2 FSCQ-Series Green Mode Fairchild Power Switch (FPS™) FSCQ0565RT Typical Application Circuit Application C-TV Output Power 59W Input Voltage Universal Input (90–270 Vac) Output Voltage (Max Current) 12V (0.5A) 18V (0.3A) 125V (0.3A) 24V (0.4A) Features ■ High Efficiency (>83% at 90 Vac Input) ■ Wider Load Range through the Extended ■ ■ ■ ■ Key Design Notes ■ 24V output is designed to drop to around 8V in standby mode Quasi-Resonant Operation Low Standby Mode Power Consumption (83% at 90 Vac Input) ■ Wider Load Range through the Extended ■ ■ ■ ■ Key Design Notes ■ 24V output is designed to drop to around 8V in standby mode Quasi-Resonant Operation Low Standby Mode Power Consumption (83% at 90 Vac Input) ■ Wider Load Range through the Extended ■ ■ ■ ■ Key Design Notes ■ 24V output is designed to drop to around 8V in standby mode Quasi-Resonant Operation Low Standby Mode Power Consumption (83% at 90 Vac Input) ■ Wider Load Range through the Extended ■ ■ ■ ■ Key Design Notes ■ 24V output is designed to drop to around 8V in standby mode Quasi-Resonant Operation Low Standby Mode Power Consumption (83% at 90Vac Input) ■ Wider Load Range through the Extended ■ ■ ■ ■ Key Design Notes ■ 24V output is designed to drop to around 8V in standby mode Quasi-Resonant Operation Low Standby Mode Power Consumption (83% at 90 Vac Input) ■ Wider Load Range through the Extended ■ ■ ■ ■ Key Design Notes ■ 24V output is designed to drop to around 8V in standby mode Quasi-Resonant Operation Low Standby Mode Power Consumption (83% at 90 Vac Input) ■ Wider Load Range through the Extended ■ ■ ■ ■ Key Design Notes ■ 24V output is designed to drop to around 8V in standby mode Quasi-Resonant Operation Low Standby Mode Power Consumption (

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