FAIRCHILD FAN7554 Versatile PWM Controller handbook
Contents
1. 10000 0 100 000 1000 0 7 10 000 N e 0 33n 9 x 100 0 1 1n p 2 2 amp 3 3n A 5K g 10 0 E 9 3 10K E 8 1000 si 10 1 100K 0 1 0 100 1 10 100 0 1 1 10 100 Rt Kohm Ct nF Figure 1 Rt vs Frequency Figure 2 Ct vs Dead Time 800 95 0 1 54 700 85 0 600 75 0 1k GER 2K 500 S 2 k S 5K 2 400 e Tr 2 55 0 A 10K 8 x 20K E 45 0 e 50K 300 in 100K geg 25 0 100 15 0 0 0 1 10 100 1 10 100 Ct nF Cload nF Figure 3 Ct vs Duty Figure 4 Cload vs Tr amp Tf FAN7554 Typical Performance Characteristics continued Start up Ist mA 25 0 25 50 75 100 Temperature Tj Figure 5 Temperature vs Start up Current 4 960 gt 8 D FS 8 8 a S Reference voltage Vref V o 25 50 75 100 Temperature Tj Figure 7 Temperature vs Reference Voltage o R 14 7 14 6 Start threshold2. Capacitor Ct is charged to almost 2 8V through resistor Rt from the 5V reference and discharged to 1 2 by an internal current source The oscillator generates the clock signal while the timing capacitor Ct is discharged The gate drive output becomes low during the clock time Rt and Ct selection determine the oscillator frequency and maximum duty cycle Charge and discharge times can be calculated through the equations below Charging time tc 0 55xRtxCt Discharging time td RtxCtxIn 0 0063xRt 2 8 0 0063xRt 3 8 where the oscillator frequency fosc tc td 10 When Rt gt 5kQ fosc 1 0 55xRxCt 1 8 RexCt Vhigh 2 8V rq Sawtooth waveform Vlow 1 2V 1 Rt 5kQ Gate priye Internal clock Sawtooth waveform Vlow 1 2V bs Rt lt 5kQ FAN7554 E i j 1 1 intemal cloak 2 Figure 14 Oscillator Circuit Figure 15 Sawtooth amp Clock Waveform FAN7554 Feedback As shown in figurel6 the internal oscillator clock turns on the MOSFET The feedback comparator operates to turn it off again when the MOSFET current reaches a set value proportional to Vfb The feedback capacitor Cfb is charged by the inter nal current sources mA and 50 and is discharged by the secondary side photo coupler to control the output voltage DRIN Vsense ML 3 FAN7554 Rs Figure 16 Feedback
3. 85 265 50 60Hz 14 7554 Part List FAN7554 Flyback Converter Demo Board Part Value Note Part Value Note FUSE CAPACITOR FUSE 250 2A C101 100nF 275V Box Capacitor NTC C102 100nF 275V Box Capacitor NTC 5D 11 C103 470nF 400WV Electrolytic RESISTOR C104 103 1kV Film Capacitor R101 330kQ 1W C105 104 Ceramic R102 C106 1uF 10V Electrolytic R103 R104 100kQ 1W C107 101 Ceramic R105 220 C108 122 Ceramic R106 4 7 109 22uF 50V Electrolytic R107 12kQ C201 330uF Electrolytic R108 100 C202 330uF Electrolytic R109 1 C203 104 Ceramic R110 0 50 2W C301 R201 1kQ C302 R202 1kQ R203 4 7kQ INDUCTOR R204 1 2 LF101 30mH R205 L201 6 4uH MOSFET DIODE Q101 FQP6N70 Fairchild D201 MBRF10100CT IC D101 UF4007 Fairchild IC101 FAN7554 Fairchild D102 1N4148 IC201 431 Fairchild D103 UF4004 Fairchild IC301 Opto coupler Fairchild BD G3SBA60 15 FAN7554 Transformer Specification Schematic Diagram Top view bottom top Winding Specification No Pin S gt F Wire Turns Winding Method Np 123 0 350 x 1 44 N12V 711 0 350 x 4 12 NP 123 0 350 x 1 44 NB 5 4 0 350 1 13 Electrical Characteristic Closure Pin Spec Remarks Inductance 1 3 400uH 10 100kHz 1V Leakagel 1 3 10uH MAX 2d All
4. Specification 13 14 e Ns 12 8 9 Ns 5 4turn 10 11 12 2 Np 32turn Ns 12 5turn Ns 5 4turn Np 32turn 2 Core Powder 27 16grade 5V 127 10x2 12V 27T 1 20 x1 No Pin S gt F Wire Turns NP 133 0 650 x 1 32 Ns 5 8o 11 0 650 x4 4 Ns 12 4 9 0 65 4 5 1 gt 3 0 650 x 1 32 736 0 650 x1 5 FAN7554 Mechanical Dimensions Package Dimensions in millimeters la e 6 5 8 HA ALA 1 PIN 2 IDICATOR Pla TT C pod _ d EATING ANE Symbol Min Nom Max A 1 75 A1 0 10 0 15 0 25 A2 1 25 1 45 1 50 B 0 35 0 37 0 51 C 0 19 0 20 0 25 D 4 80 4 90 5 00 E 3 80 3 90 4 00 e 1 27BSC H 5 79 5 99 6 20 h 0 25 0 50 L 0 50 0 70 0 90 GP 0 36 BSC q 0 8 aaa 0 25 bbb 0 10 20 7554 Mechanical Dimensions continued Package Dimensions in millimeters 8 DIP 6 40 0 20 T 0 252 0008 0 060 0004 0 362 10108 le NIS UGS 3 30 0 30 us 0 130 some 0 300 3 40 40 20 p 0 134 21 FAN7554 Ordering Information Product Number Package Operating Temperature FAN7554 8 DIP 25 C 85 C FAN7554D 8 SOP DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE C
5. That is the FAN7554 needs the time to detect and decide whether it is an overload condition or not The protection circuit can be prevented from operating during transient states by ensuring that a certain amount of time passes before the protection circuit operates The above operations are executed as follows Since the FAN7554 adopts a current mode it is impossible for current to flow above a maximum level For a fixed input voltage this limits power Therefore if the power at the output exceeds this maximum Vo shown in figure21 becomes less than the set voltage and the KA43 Ipulls in only the given minimum current As a result the photo coupler s secondary side current becomes zero The same goes for the photo coupler s primary side current Consequently when the full current 1mA flows through the internal resistor QR Vfb becomes approximately and from that time the 50 current source begins to charge Cfb the photo coupler s secondary current is almost zero The FAN7554 shuts down when Vfb reaches 6V Shutdown UVLO out OSC FAN7554 KA431 FB ev Shutdown start point t 2 ti 4 Time Constant Cfb 4 2 t 5uA Cfb 3V t2 Figure 21 Delayed Shutdown 13 FAN7554 FAN7554 Flyback Converter Demo Circuit Fsw 100kHz pou 12V 3 5A O C301 C302 R205 C203 Input
6. amp PWM Circuit Delayed Shutdown During the normal operation the feedback voltage is between 0 3V If the output terminal overloads or an error happens to the feedback loop the delayed shutdown circuit operates When the feedback voltage is less than 3V the feedback capacitor is charged by current sources 1mA and SuA when the feedback voltage becomes greater than the capacitor is charged by the 5uA current source because diode D1 turns off When the feedback voltage is less than the charge slope becomes expo nential function and when it is greater than 3V the charge slope becomes linear When the feedback voltage reaches almost 6V the FAN7554 shuts down The shut down circuit is configured for auto restart so it automatically restarts when Vcc reaches the under voltage 9V DRIN Rs Over Current Comparator Shutdown 7554 UVLO out Figure 17 A Delayed Shutdown amp Feedback Circuit 10 7554 Vfb 6V Slope dv dt 5uA y Shutdown start point Figure 17 B Delayed Shutdown amp Feedback Waveform Gate Driver The gate drive circuit has the totem pole output configuration The output has 1A peak current and 200mA average current drive ability DRAIN Shutdown FAN7554 Figure 18 Gate Drive Circuit ON OFF Control The FAN7554 is able to use the feedback pin for ON OFF control by placing NPN tra
7. CTION gt Off mode sink current ISINK VFB lt VTH FB VS S 5V 4 mA Off threshold voltage VOFF VFB lt VTH FB 1 2 15 1 8 V lt SOFT START SECTION gt Soft start current 15 5 VFB 5V Vs s OV 1 1 mA Soft start limit voltage VLIM S S Vcc 16V S 5 2 V OUTPUT SECTION gt Low output voltage1 VOL1 VCC 18V lo 50mA 0 15 0 4 V High output voltage1 VOHI Vcc 18V lo 50mA 13 15 17 V Low output voltage2 VOL2 Voc 18V lo 200mA 1 5 2 5 V High output voltage2 VoH2 Vcc 18V lo 200mA 12 14 16 V Rising time Note1 tR Tj 25 C CL 1nF 80 ns Falling time Note1 tF Tj 25 CL 1nF 40 ns UVLO SECTION gt Start threshold voltage VTH ST 13 2 15 16 2 V Min operating voltage VOPR M 8 2 9 10 2 V 7554 Electrical Characteristics continued Ta 25 Vcc 16V Rt 10kQ Ct 3 3nF unless otherwise specified Parameter Symbol Conditions Min Typ Max Unit TOTAL STAND BY CURRENT SECTION Start up current IST 0 1 0 2 mA Operating supply current 7 10 Off State current loFF VFB lt VTH FB VS S lt VOFF 0 2 0 4 mA Note 1 These parameters although guaranteed are not 10096 tested in production FAN7554 Typical Perfomance Characteristics
8. D Ground 6 OUT Output of gate driver 7 Vcc Power supply 8 Vref Output of 5V reference FAN7554 Electrical Characteristics Ta 25 C Vcc 16V Rt 10kQ Ct 3 3nF unless otherwise specified Parameter Symbol Conditions Min Typ Max Unit lt REFERENCE SECTION gt Reference output voltage VREF Tj 25 C Iref 1mA 4 90 5 00 5 10 V Line regulation AVREF1 Vcc 12V 25V 6 20 mV Load regulation AVREF2 Iref 1mA 20mA 6 25 mV Short circuit output current ISC Tj 25 C 0 1 0 18 A lt OSCILLATOR SECTION gt Oscillation frequency FOSC Tj 25 C 45 50 55 kHz Frequency change with Vcc AFOSC1 Vcc 12V 25V 0 05 1 0 Ramp high voltage VRH 2 8 V Ramp low voltage VRL 1 2 V Discharge current Idisch VRT CT 3 3V 6 1 9 4 mA lt PWM SECTION gt Sense threshold voltage VTH IS VFB DN 0 8 1 0 1 2 V Feedback threshold voltage VTH FB VIS OV 0 2 0 3 0 4 V Feedback source current IFB VFB OV Vg s 5V 1 0 mA Max duty cycle D MAX 2 92 95 98 96 Min duty cycle D MIN 5 x 0 lt PROTECTION SECTION gt Shutdown delay current ISD 4V lt VFB lt VSD 3 5 5 6 5 uA Shutdown feedback voltage VSD VFB gt 5V 5 4 6 6 6 V Over current protection Voc Vis gt 1 5V ton gt 500nS 1 6 2 2 4 V Over voltage protection VOVP 30 34 38 V lt ON OFF CONTROL SE
9. FAIRCHILD SEMICONDUCTOR www fairchildsemi com FAN 7554 Versatile PWM Controller Features e Current mode control Pulse by pulse current limiting Low external components Under voltage lockout UVLO 9V 15V Stand by current typ 100uA Power saving mode current typ 200uA Operating current typ 7mA Soft start On off control Over load protection OLP Over voltage protection OVP Overcurrent protection OCP Over current limit OCL e Operating frequency up to S00kHz 1A totem pole output current Applications Off Line amp DC DC converter Description The FAN7554 is a fixed frequency current mode PWM controller It is specially designed for off line and DC to DC converter applications with minimal external components These integrated circuits feature a trimmed oscillator for precise duty cycle control a temperature compensated reference an ON OFF control a high gain error amplifier a current sensing comparator and a high current totem pole output The FAN7554 has various protection functions such as an over load protection an over current protection and the over voltage protection which include built in auto restart circuit The FAN7554 is available in the 8 DIP package as well as the 8 SOP package 8 DIP Rev 1 0 3 2003 Fairchild Semiconductor Corporation FAN7554 Internal Block Diagram Offset 0 1V Absolute M
10. HANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY FUNCTION OR DESIGN FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS NOR THE RIGHTS OF OTHERS LIFE SUPPORT POLICY FAIRCHILD S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION As used herein 1 Life support devices or systems are devices or systems which a are intended for surgical implant into the body or b support or sustain life and c whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in a significant injury of the user www fairchildsemi com 2 A critical component in any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness 10 2 03 0 0m 001 Stock DSxxxxxxxx 2003 Fairchild Semiconductor Corporation
11. ating during transient states by ensuring that a certain amount of the time passes before the protection circuit operates The shutdown circuit is configured for an auto restart so the FAN7554 automatically restarts when Vcc drops to 9V stop voltage Start Up The start up circuit is made up of an under voltage lock out UVLO the protection for low voltage conditions and the 5V reference Vref which supplies bias voltage to the control circuit after start up The start voltage of the UVLO is 15 and the stop voltage after turn on is 9V It has a 6V hysteresis The minimum operating current for start up threshold is typically 100uA and this can reduce the power dissipation on the start up resistor The Vref is composed of the band gap reference circuit with its superior temperature characteristics and supplies power to all the FAN7554 circuits and R Ct with the exceptions of the ULVO circuit and ON OFF control circuit UVLO 5V Internal bias Vref Good logic 15V 9V i 9 15 Figure 11 Low Current Start Up amp Bandgap Reference Circuit Figure 12 Start Up amp Circuit Characteristics Soft Start The SMPS output load usually contains capacitive load component During initial start up the output voltage increases at fixed time constant because of this component If the feedback loop which controls the output voltage was to start without the soft start circuit the feedback loop would appear to
12. aximum Ratings Ta 25 C unless otherwise specified Parameter Symbol Value Unit Supply voltage Vcc 30 V Output current lo 1 Input voltage to FB VFB 0 3 to VSD V Input voltage to IS pin VIS 0 3 to Voc V Power dissipation at TA lt 25 8 DIP PD 0 85 8 SOP 0 42 Operating temperature 25 10 85 C Storage temperature TSTG 55 to 150 Thermal resistance junction to air Note1 8 DIP R6ja 147 8 C W 8 SOP 291 4 Note 1 Junction to air thermal resistance test environments JESD51 2 Integrated circuits thermal test method environmental conditions natural convection still air JESD51 3 Low effective thermal conductivity test board for leaded surface mount packages JESD51 10 Test boards for through hole perimeter leaded package thermal measurements 7554 Temperature Characteristics 25 C lt lt 85 C Parameter Symbol Value Unit Vref temperature stability AVREF3 40 5 Fosc temperature stability AFOSC2 5 PIN Array Vref OUT GND PIN Definitions Y WW C FAN7554 FB S S IS Rt Ct Pin Number Pin Name Pin Function Description 1 FB Inverting input of pwm comparator on off control amp OLP sensing terminal 2 S S Soft start 3 IS Non inverting input of PWM comparator OCL sensing terminal 4 Rt Ct Oscillator time constant Rt Ct 5 GN
13. be open during initial start up so at start up the feedback voltage applied to the PWM comparator s inverting input reaches its maximum value 1 V During this time the peak value of the drain current would stay at the maximum value and the maximum power would be delivered to the secondary load side from the start When the maximum power is delivered to the secondary side for this initial fixed time the entire circuit is seriously stressed The use of a soft start can avoid such stresses At start up the soft start capacitor Cs is charged by 1mA and 100uA current sources The voltage of the inverting terminal of the PWM comparator increases to 1 3 of the Cs voltage at a fixed time constant Subsequently the drain peak current is limited by the gradual increase in the Cs voltage and this causes the output voltage to increase smoothly When the Cs voltage becomes greater than 3V the diode Ds turns off consequently the feedback capacitor Cfb is charged by 1mA and 50 current sources This charge voltage determines the comparator s inverting voltage Then Cs voltage charges to 5V by 100uA current source The soft start capacitor Cs is discharged when the UVLO good logic starts so the soft start is repeated at re start 7554 Output drive FAN7554 Figure 13 Soft Start Circuit amp Circuit Flow Oscillator As shown in figurel4 the oscillator frequency is programmed by values selected for timing components Rt and Ct
14. nsistor between the cathode of the KA431 and ground as shown in figure 19 When the transistor turns on the current flows through the photo diode and saturates the photo transistor As a result the feedback voltage is dropped to zero When the feedback voltage is below 0 3V the soft start voltage starts to discharge by connecting the internal resistor 1kQ in parallel with the external capacitor Cs When the soft start voltage becomes less than 1 5V all the blocks in the FAN7554 are turned off with the exceptions of the UVLO block and ON OFF control block The operation current is about 200uA So the stand by power is reduced and SMPS efficiency is improved When the feedback voltage exceeds 0 3V the FAN7554 normally operates by turning on Vref block 11 FAN7554 Good logic Internal bias Remote control Figure 19 ON OFF Control Circuit Vref 5V Vsis Slope dv dt 100uA 5V Slope dv dt 1kO Cs i Slope dv dt 1 100uA Cs 1 5V MERI sd Slope dv dt IMA 5A Cfb 0 3V E eerte ht EE m Normal State e OFF State e Normal State gt Figure 20 ON OFF Control Circuit Waveforms 12 7554 Protection Circuits The FAN7554 has many built in protection circuits that do not need additional components providing reliability without cost increase These protection circuits have the auto restart configurati
15. on In this configuration the protection circuits reset when is below UVLO stop threshold 9V and restarts when is above UVLO start threshold voltage 15V Over Voltage Protection Abnormalities may occur in the SMPS secondary side feedback circuit First when the feedback pin is short to the ground the feedback voltage is zero and the FAN7554 is unable to start switching Second when the feedback circuit is open the secondary voltage generally becomes much greater than the rated voltage as the primary side continues to switch at the maximum current level This may cause the blowing off the fuse or in serious cases fires It is possible that the devices directly connected to the secondary output without a regulator could be destroyed Even in these cases the over voltage protection circuit operates Since Vcc is proportional to the output in an over voltage situation it also will increase In the FAN7554 the protection circuit operates when Vcc exceeds 34V Therefore mm normal operation must be set below 34 Over Load Protection An overload is the state in which the load is operating normally but in excess of the preset load The overload protection circuit can force the FAN7554 to stop its operation The protection can also operate in transient states such as initial SMPS operation Because the transient state returns to the normal state after a fixed time the protection circuit need not to operate during this time
16. short 16 7554 FAN7554 forward converter demo circuit fsw 100kHz T101 12 2 L 5V 3A L 7 ef Vcc FAN7554 F B S S IS RUCt Input 85 265Vac 50 60Hz 17 FAN7554 Part List For FAN7554 Forward Converter Demo Board Part Value Note Part Value Note FUSE CAPACITOR FUSE 250 2A C101 470nF 275V Box Capacitor NTC C102 C103 470nF 400WV Electrolytic RT101 DSC 100 11 C104 223 630V Film RESISTOR C105 33uF 35V Film Capacitor R101 330kQ 1W C106 104 Ceramic R102 C107 1uF 35V Electrolytic R103 R104 56kQ 1W C108 101 Ceramic R105 R106 220kQ 1W C109 122 Ceramic R107 100 C110 272 Film R108 200 C111 333 Film R109 4 7 201 202 1000uF 35V Electrolytic R110 1 2kQ C203 330uF 16V Electrolytic R111 0 50 0 50 0 50 2W C204 2200uF 16V Electrolytic R112 1 205 104 Ceramic R113 12kQ C301 C302 332 1kV Ceramic R201 R202 10kQ INDUCTOR R203 1kQ LF101 30mH R204 3300 L201 MOSFET DIODE Q101 SSH8N80 Fairchild D101 1N4004 IC D102 FR157 IC101 FAN7554 Fairchild D103 UF4007 IC201 431 Fairchild D201 MBRF10100CT IC301 Opto Coupler Fairchild D202 MBR3045PT BD PBS406GU 18 7554 Transformer specification Schematic Diagram Top view e Np 32turn 3 6 5turn 7 Winding
17. voltage Vth st V 25 0 25 50 75 100 Temperature Tj Figure 9 Temperature vs Start Threshold Voltage 24 o o I Operating supply current lop mA o o o o a S o 25 50 75 100 Temperature Tj C Figure 6 Temperature vs Operating Supply Current 540 534 Oscillation frequency Fosc KHz 25 0 25 50 75 100 Temperature Tj CC Figure 8 Temperature vs Oscillation frequency 932 929 Se 9 28 927 Min operating voltage Vopr min V 25 0 25 50 15 100 Temperature Tj Figure 10 Temperature vs Min Operating Voltage FAN7554 Operation Description The FAN7554 has all the basic features of the current mode SMPS control IC Its basic configuration includes the UVLO with 6V hysteresis a band gap reference the oscillator that can oscillate up to 500kHz according to Rt Ct connected externally PWM logic circuit a gate driver and the feedback circuit that has the current source and soft start function The FAN7554 has various functions such as an over load protection an over current protection and an over voltage protection The over load protection forces the FAN7554 to stop its operation if the load current is higher than the preset value The protection circuit can also be prevented from oper
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FAIRCHILD FAN7554 Versatile PWM Controller handbook