FAN7621S PFM Controller for Half-Bridge Resonant Converters Features Description Variable Frequency Control with 50% Duty Cycle for Half-bridge Resonant Converter Topology High Efficiency through Zero Voltage Switching (ZVS) Fixed Dead Time: 350ns Up to 300kHz Operating Frequency Auto-Restart Operation for All Protections with an External LVCC Protection Functions: Over-Voltage Protection (OVP), Over-Current Protection (OCP), Abnormal Over-Current Protection (AOCP), Internal Thermal Shutdown (TSD) Applications PDP and LCD TVs Desktop PCs and Servers Adapters Telecom Power Supplies Video Game Consoles The FAN7621S is a pulse frequency modulation controller for high-efficiency half-bridge resonant converters. Offering everything necessary to build a reliable and robust resonant converter, the FAN7621S simplifies designs and improves productivity, while improving performance. The FAN7621S includes a highside gate-drive circuit, an accurate current-controlled oscillator, frequency-limit circuit, soft-start, and built-in protection functions. The high-side gate-drive circuit has a common-mode noise cancellation capability, which guarantees stable operation with excellent noise immunity. Using the zero-voltage-switching (ZVS) technique dramatically reduces the switching losses and significantly improves efficiency. The ZVS also reduces the switching noise noticeably, which allows a smallsized Electromagnetic Interference (EMI) filter. The FAN7621S can be applied to various resonant converter topologies; such as series resonant, parallel resonant, and LLC resonant converters. Related Resources AN4151 — Half-Bridge LLC Resonant Converter Design TM Using FSFR-Series Fairchild Power Switch (FPS ) Ordering Information Part Number Operating Junction Temperature FAN7621SSJ FAN7621SSJX © 2009 Fairchild Semiconductor Corporation FAN7621S • Rev. 1.0.1 -40°C to +130°C Package 16-Lead, Small Outline Package (SOP) Packaging Method Tube Tape & Reel www.fairchildsemi.com FAN7621S — PFM Controller for Half-Bridge Resonant Converters July 2010 Cr V IN VCC VO LVCC Rmin RT Rmax Rss Css AR FAN7621S HVCC HO CTR LO CS SG PG Figure 1. Typical Application Circuit (LLC Resonant Half-Bridge Converter) Block Diagram LVCC 12 Vre f Vre f 1 IR T IR T 2IR T LV 3V S 1V R CC g o od HVcc In tern al B ias Vr e f Q L U V+ / L U V- H UV+ / H UV- 2V RT Level S hifter T ime D elay 8 H ig h S id e Gate D river 350ns 3 2 HO CTR D ivider AR 6 5k B alan cin g D elay T ime D elay VC s s H/ VC s s L L ow S id e Gate D river 14 LO 350ns S LV CC R g o od Sh utd own with o ut d elay Q TS D L VC C VO V P VA O C P D elay 50n s 16 PG 10 SG VO C P D elay 1.5µs -1 9 CS Figure 2. Internal Block Diagram © 2009 Fairchild Semiconductor Corporation FAN7621S • Rev. 1.0.1 www.fairchildsemi.com 2 FAN7621S — PFM Controller for Half-Bridge Resonant Converters Application Circuit Diagram FAN7621S — PFM Controller for Half-Bridge Resonant Converters Pin Configuration (1) H V CC P G (16 ) (2) C T R N C (15 ) (3) H O L O (14 ) (4) N C FAN7 6 21S N C (13 ) (5) N C L V C C (12 ) (6) A R N C (11 ) (7) N C S G (10 ) (8) R T CS (9) Figure 3. Package Diagram Pin Definitions Pin # Name Description 1 HVCC This is the supply voltage of the high-side gate-drive circuit IC. 2 CTR This is the drain of the low-side MOSFET. Typically, a transformer is connected to this pin. 3 HO This is the high-side gate driving signal. 4 NC No connection 5 NC No connection 6 AR This pin is for discharging the external soft-start capacitor when any protection is triggered. When the voltage of this pin drops to 0.2V, all protections are reset and the controller starts to operate again. 7 NC No connection 8 RT This pin programs the switching frequency. Typically, an opto-coupler is connected to control the switching frequency for the output voltage regulation. 9 CS This pin senses the current flowing through the low-side MOSFET. Typically, negative voltage is applied on this pin. 10 SG This pin is the control ground. 11 NC No connection 12 LVCC 13 NC No connection 14 LO This is the low-side gate driving signal. 15 NC No connection 16 PG This pin is the power ground. This pin is connected to the source of the low-side MOSFET. This pin is the supply voltage of the control IC. © 2009 Fairchild Semiconductor Corporation FAN7621S • Rev. 1.0.1 www.fairchildsemi.com 3 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 Parameter Min. Max. Unit VHO High-Side Gate Driving Voltage VCTR-0.3 HVCC VLO Low-Side Gate Driving Voltage -0.3 LVCC Low-Side Supply Voltage -0.3 25.0 V -0.3 25.0 V -0.3 600.0 V LVCC HVCC to VCTR High-Side VCC Pin to Center Voltage V VCTR Center Voltage VAR Auto-Restart Pin Input Voltage -0.3 LVCC V VCS Current Sense (CS) Pin Input Voltage -5.0 1.0 V VRT RT Pin Input Voltage -0.3 5.0 V 50 V/ns 1.13 W dVCTR/dt PD TJ TSTG Allowable Center Voltage Slew Rate Total Power Dissipation Maximum Junction Temperature (1) +150 (1) Recommended Operating Junction Temperature -40 +130 Storage Temperature Range -55 +150 °C °C Note: 1. The maximum value of the recommended operating junction temperature is limited by thermal shutdown. Thermal Impedance Symbol θJA Parameter Junction-to-Ambient Thermal Impedance © 2009 Fairchild Semiconductor Corporation FAN7621S • Rev. 1.0.1 Value Unit 110 ºC/W www.fairchildsemi.com 4 FAN7621S — PFM Controller for Half-Bridge Resonant Converters Absolute Maximum Ratings TA=25°C and LVCC=17V unless otherwise specified. Symbol Parameter Test Conditions Min. Typ. Max. Unit 50 μA Supply Section ILK Offset Supply Leakage Current HVCC=VCTR IQHVCC Quiescent HVCC Supply Current (HVCCUV+) - 0.1V 50 120 μA IQLVCC Quiescent LVCC Supply Current (LVCCUV+) - 0.1V 100 200 μA IOHVCC Operating HVCC Supply Current (RMS Value) fOSC=100kHz, CLoad=1nF 5 8 mA 100 200 μA IOLVCC Operating LVCC Supply Current (RMS Value) fOSC=100kHz, CLoad=1nF 6 9 mA No Switching 2 4 mA No Switching UVLO Section LVCCUV+ LVCC Supply Under-Voltage Positive-Going Threshold (LVCC Start) 11.2 12.5 13.8 V LVCCUV- LVCC Supply Under-Voltage Negative-Going Threshold (LVCC Stop) 8.9 10.0 11.1 V LVCCUVH LVCC Supply Under-Voltage Hysteresis HVCCUV+ HVCC Supply Under-Voltage Positive-Going Threshold (HVCC Start) 8.2 9.2 10.2 V HVCCUV- HVCC Supply Under-Voltage Negative-Going Threshold (HVCC Stop) 7.8 8.7 9.6 V HVCCUVH HVCC Supply Under-Voltage Hysteresis 2.5 V 0.5 V Oscillator & Feedback Section VRT V-I Converter Threshold Voltage fOSC Output Oscillation Frequency DC Output Duty Cycle fSS Internal Soft-Start Initial Frequency tSS Internal Soft-Start Time RT=5.2kΩ 1.5 2.0 2.5 V 94 100 106 kHz 48 50 52 % 140 fSS=fOSC+40kHz, RT=5.2kΩ 2 3 kHz 4 ms Output Section Isource Isink Peak Sourcing Current HVCC=17V 250 360 mA Peak Sinking Current HVCC=17V 460 600 mA 65 ns 35 ns tr Rising Time tf Falling Time VHOH High Level of High-Side Gate Driving Signal (VHVCC-VHO) VHOL Low Level of High-Side Gate Driving Signal VLOH High Level of High-Side Gate Driving Signal (VLVCC-VLO) VLOL Low Level of High-Side Gate Driving Signal © 2009 Fairchild Semiconductor Corporation FAN7621S • Rev. 1.0.1 CLoad=1nF, HVCC=17V 1.0 V 0.6 V 1.0 V 0.6 V IO=20mA www.fairchildsemi.com 5 FAN7621S — PFM Controller for Half-Bridge Resonant Converters Electrical Characteristics TA=25°C and LVCC=17V unless otherwise specified. Symbol Parameter Test Conditions Min. Typ. Max. Unit Protection Section VCssH Beginning Voltage to Discharge CSS 0.9 1.0 1.1 V VCssL Beginning Voltage to Charge CSS and Reset Protections 0.16 0.20 0.24 V VOVP LVCC Over-Voltage Protection LVCC > 21V 21 23 25 V VAOCP AOCP Threshold Voltage ΔV/Δt=-0.1V/µs -1.0 -0.9 -0.8 V tBAO AOCP Blanking Time VCS < VAOCP; ΔV/Δt=-0.1V/µs VOCP OCP Threshold Voltage ΔV/Δt=-1V/µs -0.64 -0.58 -0.52 V 1.0 1.5 2.0 μs 250 400 ns 130 150 °C (2) tBO OCP Blanking Time VCS < VOCP; ΔV/Δt=-1V/µs tDA Delay Time (Low-Side) Detecting from (2) VAOCP to Switch Off ΔV/Δt=-1V/µs TSD Thermal Shutdown Temperature (2) (2) 50 110 ns Dead-Time Control Section DT (3) Dead Time 350 ns Notes: 2. These parameters, although guaranteed, are not tested in production. 3. These parameters, although guaranteed, are tested only in EDS (wafer test) process. © 2009 Fairchild Semiconductor Corporation FAN7621S • Rev. 1.0.1 www.fairchildsemi.com 6 FAN7621S — PFM Controller for Half-Bridge Resonant Converters Electrical Characteristics (Continued) 1.1 1.1 1.05 1.05 Normalized at 25OC Normalized at 25OC These characteristic graphs are normalized at TA=25ºC. 1 0.95 1 0.95 0.9 0.9 -50 -25 0 25 50 75 -50 100 -25 0 Temp (OC) 25 50 75 100 Temp (OC) Figure 4. Low-Side MOSFET Duty Cycle Figure 5. Switching Frequency vs. Temperature 1.1 1.1 1.05 1.05 Normalized at 25OC Normalized at 25OC vs. Temperature 1 0.95 0.9 1 0.95 0.9 -50 -25 0 25 50 75 100 -50 -25 0 Temp (OC) Figure 6. High-Side VCC (HVCC) Start vs. Temperature 50 75 100 Figure 7. High-Side VCC (HVCC) Stop vs. Temperature 1.1 1.1 1.05 1.05 Normalized at 25OC Normalized at 25OC 25 Temp (OC) 1 0.95 1 0.95 0.9 0.9 -50 -25 0 25 50 75 -50 100 -25 0 25 50 75 100 Temp (OC) Temp (OC) Figure 8. Low-Side VCC (LVCC) Start vs. Temperature Figure 9. Low-Side VCC (LVCC) Stop vs. Temperature © 2009 Fairchild Semiconductor Corporation FAN7621S • Rev. 1.0.1 www.fairchildsemi.com 7 FAN7621S — PFM Controller for Half-Bridge Resonant Converters Typical Performance Characteristics 1.1 1.1 1.05 1.05 Normalized at 25OC Normalized at 25OC These characteristic graphs are normalized at TA=25ºC. 1 0.95 0.9 1 0.95 0.9 -50 -25 0 25 50 75 100 -50 -25 0 Temp (OC) Figure 10. LVCC OVP Voltage vs. Temperature 50 75 100 Figure 11. RT Voltage vs. Temperature 1.1 1.05 1.05 Normalized at 25 1.1 Normalized at 25 25 Temp (OC) 1 0.95 1 0.95 0.9 0.9 -50 -25 0 25 50 75 100 -50 Temp( ) -25 0 25 50 75 100 Temp( ) Figure 12. VCssL vs. Temperature Figure 13. VCssH vs. Temperature 1.1 Normalized at 25OC 1.05 1 0.95 0.9 -50 -25 0 25 50 75 100 Temp (OC) Figure 14. OCP Voltage vs. Temperature © 2009 Fairchild Semiconductor Corporation FAN7621S • Rev. 1.0.1 www.fairchildsemi.com 8 FAN7621S — PFM Controller for Half-Bridge Resonant Converters Typical Performance Characteristics (Continued) 1. Basic Operation: FAN7621S is designed to drive high-side and low-side MOSFETs complementarily with 50% duty cycle. A fixed dead time of 350ns is introduced between consecutive transitions, as shown in Figure 15. Figure 15. MOSFETs Gate Drive Signal 2. Internal Oscillator: FAN7621S employs a currentcontrolled oscillator, as shown in Figure 16. Internally, the voltage of RT pin is regulated at 2V and the charging / discharging current for the oscillator capacitor, CT, is obtained by copying the current flowing out of RT pin (ICTC) using a current mirror. Therefore, the switching frequency increases as ICTC increases. + 3V I CTC 2I CTC FAN7621S I CTC V REF Figure 17. Resonant Converter Typical Gain Curve 1V CT S Q R -Q + F /F - + - RT 2V 8 C oun ter (1/4) G ate drive Figure 18. Frequency Control Circuit Figure 16. Current Controlled Oscillator To prevent excessive inrush current and overshoot of output voltage during startup, increase the voltage gain of the resonant converter progressively. Since the voltage gain of the resonant converter is inversely proportional to the switching frequency, the soft-start is implemented by sweeping down the switching frequency ISS from an initial high frequency (f ) until the output voltage is established. The soft-start circuit is made by connecting R-C series network on the RT pin, as shown in Figure 18. FAN7621S also has an internal soft-start of 3ms to reduce the current overshoot during the initial cycles, which adds 40kHz to the initial frequency of the external soft-start circuit, as shown in Figure 19. The initial frequency of the soft-start is given as: 3. Frequency Setting: Figure 17 shows the typical voltage gain curve of a resonant converter, where the gain is inversely proportional to the switching frequency in the ZVS region. The output voltage can be regulated by modulating the switching frequency. Figure 18 shows the typical circuit configuration for RT pin, where the optocoupler transistor is connected to the RT pin to modulate the switching frequency. The minimum switching frequency is determined as: f min = 5.2k Ω × 100 (kHz ) Rmin (1) f ISS = ( Assuming the saturation voltage of the opto-coupler transistor is 0.2V, the maximum switching frequency is determined as: f max = ( 5.2k Ω 4.68k Ω + ) × 100( kHz ) Rmin Rmax © 2009 Fairchild Semiconductor Corporation FAN7621S • Rev. 1.0.1 5.2k Ω 5.2k Ω + ) × 100 + 40 (kHz ) Rmin RSS (3) It is typical to set the initial (soft-start) frequency two ~ three times the resonant frequency (fO) of the resonant network. (2) www.fairchildsemi.com 9 FAN7621S — PFM Controller for Half-Bridge Resonant Converters Functional Description t SS = RSS • CSS (a ) (b ) ( a) (b ) (a ) (b ) L V CC (4) V AR V C ssH V C ssL fs f ISS ICr 40kHz Control loop take over t stop tS /S (a ) P r o te ction s a r e tr igge r e d, ( b ) F S F R- U S r e sta r ts Figure 21. Self Auto-Restart Operation time 5. Protection Circuits: The FAN7621S has several selfprotective functions, such as Over-Current Protection (OCP), Abnormal Over-Current Protection (AOCP), OverVoltage Protection (OVP), and Thermal Shutdown (TSD). These protections are auto-restart mode protections, as shown in Figure 21. Figure 19. Frequency Sweeping of Soft-Start 4. Self Auto-restart: The FAN7621S can restart automatically even if a built-in protection is triggered with external supply voltage. As shown in Figure 20 and Figure 21; once any protections are triggered, M1 switch turns on and V-I converter is disabled. CSS starts to be discharged until the VCss across CSS drops to VCssL. Then all protections are reset, M1 turns off, and V-I converter resumes. The FAN7621S starts switching again with softstart. If the protections occur while VCss is under VCssL and VCssH level, the switching is terminated immediately, VCss continues to increase until reaching VCssH, then CSS is discharged by M1. Once a fault condition is detected, switching is terminated and the MOSFETs remain off. When LVCC falls to the LVCC stop voltage of 10V or the AR signal is HIGH, the protection is reset. FAN7621S resumes normal operation when LVCC reaches the start voltage of 12.5V. Figure 22. Protection Blocks 5.1 Over-Current Protection (OCP): When the sensing pin voltage drops below -0.58V, OCP is triggered and the MOSFETs remain off. This protection has a shutdown time delay of 1.5µs to prevent premature shutdown during startup. Figure 20. Internal Block of AR Pin 5.2 Abnormal Over-Current Protection (AOCP): If the secondary rectifier diodes are shorted, large current with extremely high di/dt can flow through the MOSFET before OCP is triggered. AOCP is triggered without shutdown delay when the sensing pin voltage drops below -0.9V. After protections trigger, FAN7621S is disabled during the stop-time, tstop, where VCss decreases and reaches to VCssL. The stop-time of FAN7621S can be estimated as: tstop =Css · Rss +Rmin || 5kΩ (5) 5.3 Over-Voltage Protection (OVP): When the LVCC reaches 23V, OVP is triggered. This protection is used when auxiliary winding of the transformer to supply VCC to the controller is utilized. For the soft-start time, ts/s it can be set as Equation (4). 5.4 Thermal Shutdown (TSD): If the temperature of the junction exceeds approximately 130°C, the thermal shutdown triggers. © 2009 Fairchild Semiconductor Corporation FAN7621S • Rev. 1.0.1 www.fairchildsemi.com 10 FAN7621S — PFM Controller for Half-Bridge Resonant Converters The soft-start time is three to four times the RC time constant. The RC time constant is as follows: 7. PCB Layout Guidelines: Duty imbalance problems may occur due to the radiated noise from the main transformer, the inequality of the secondary-side leakage inductances of main transformer, and so on. It is one of the dominant reasons that the control components in the vicinity of RT pin are enclosed by the primary current flow pattern on PCB layout. The direction of the magnetic field on the components caused by the primary current flow is changed when the high- and low-side MOSFET turns on by turns. The magnetic fields with opposite direction from each other induce a current through, into, or out of the RT pin, which makes the turn-on duration of each MOSFET different. It is strongly recommended to separate the control components in the vicinity of RT pin from the primary current flow pattern on PCB layout. Error! Reference source not found. shows an example for the duty-balanced case. The yellow and blue lines show the primary current flows when the lower-side and higherside MOSFETs turn on, respectively. The primary current does not enclose any component of controller. Figure 23. Half-Wave Sensing Figure 24. Full-Wave Sensing Figure 25. Example for Duty Balancing © 2009 Fairchild Semiconductor Corporation FAN7621S • Rev. 1.0.1 www.fairchildsemi.com 11 FAN7621S — PFM Controller for Half-Bridge Resonant Converters 6. Current Sensing Using Resistor: FAN7621S senses drain current as a negative voltage, as shown in Figure 23 and Figure 24. Half-wave sensing allows low power dissipation in the sensing resistor, while full-wave sensing has less switching noise in the sensing signal. FAN7621S — PFM Controller for Half-Bridge Resonant Converters Physical Dimensions Figure 26. 16-Lead Small Outline Package (SOP) Package drawings are provided as a service to customers considering Fairchild components. Drawings may change in any manner without notice. Please note the revision and/or date on the drawing and contact a Fairchild Semiconductor representative to verify or obtain the most recent revision. Package specifications do not expand the terms of Fairchild’s worldwide terms and conditions, specifically the warranty therein, which covers Fairchild products. Always visit Fairchild Semiconductor’s online packaging area for the most recent package drawings: http://www.fairchildsemi.com/packaging/. © 2009 Fairchild Semiconductor Corporation FAN7621S • Rev. 1.0.1 www.fairchildsemi.com 12 FAN7621S — PFM Controller for Half-Bridge Resonant Converters © 2009 Fairchild Semiconductor Corporation FAN7621S • Rev. 1.0.1 www.fairchildsemi.com 13