FA3641P_00 FUJI | Alldatasheet
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- 3 SUSETRIG
FUJI Power Supply Control IC PWM Control IC with Light Load Power Saving Function FA3641P/N FA3647P/N Application Note oo
1 SLEETRIE
1.This Data Book contains the product specifications, characteristics, data, materials, and structures as of July 2000. The contents are subject to change without notice for specification changes or other reasons. When using a product listed in this Data Book, be sure to obtain the latest specifications. 2. All applications described in this Data Book exemplify the use of Fuji's products for your reference only. No right or license, either express or implied, under any patent, copyright, trade secret or other intellectual property right owned by Fuji Electric Co., Ltd. is (or shall be deemed) granted. Fuji makes no representation or warranty, whether express or implied, relating to the infringement or alleged infringement of other's intellectual property rights which may arise from the use of the applications described herein. 3. Although Fuji Electric is enhancing product quality and reliability, a small percentage of semiconductor products may become faulty. When using Fuji Electric semiconductor products in your equipment, you are requested to take adequate safety measures to prevent the equipment from causing a physical injury, fire, or other problem if any of the products become faulty. It is recommended to make your design failsafe, flame retardant, and free of malfunction. 4.The products introduced in this Data Book are intended for use in the following electronic and electrical equipment which has normal reliability requirements. *Computers +*OA equipment + Communications equipment (terminal devices) * Measurement equipment + Machine tools + Audiovisual equipment Electrical home appliances +Personalequipment — « Industrial robots etc. 5.If you need to use a product in this Data Book for equipment requiring higher reliability than normal, such as for the equipment listed below, it is imperative to contact Fuji Electric to obtain prior approval. When using these products for such equipment, take adequate measures such as a backup system to prevent the equipment from malfunctioning even if a Fuji's product incorporated in the equipment becomes faulty. + Transportation equipment (mounted on cars and ships) + Trunk communications equipment * Traffic-signal control equipment * Gas leakage detectors with an auto-shut-off feature + Emergency equipment for responding to disasters and anti-burglary devices + Safety devices 6. Do not use products in this Data Book for the equipment requiring strict reliability such as (without limitation) * Space equipment + Aeronautic equipment * Atomic contro! equipment + Submarine repeater equipment * Medical equipment 7. Copyright © 1995 by Fuji Electric Co., Ltd. All rights reserved. No part of this Data Book may be reproduced in any form or by any means without the express permission of Fuji Electric. 8. If you have any question about any portion in this Data Book, ask Fuji Electric or its sales agents before using the product. Neither Fuji nor its agents shall be liable for any injury caused by any use of the products not in accordance with instructions set forth herein. -—— MmvrEUUI Cl
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- Description The FA3641 and FA3647 are the PWM type switching power supply control ICs that can directly drive power MOSFET. These ICs use a CMOS device with high dielectric strength (30V) to implement low power consumption. They feature a number of functions that are equivalent to those of the FA531x series consisting of bipolar devices. _ In addition, they have a function that reduces the oscillation frequency to suppress loss in light load mode and support an overvoltage protection function detecting Vcc voltage. These ICs are most suitable for high-performance, energy-saving power supplies that require low input power in standby or no-load mode. 2. Features - Uses a newly developed CMOS process with high dielectric strength (30V) for implementing low power consumption - Standby current of 21A or less (at Vec = 14V), and operating current of 1.9mA (typ) - Automatically reduces the oscillation frequency to suppress loss in light load mode - Overvoltage protection function that detecting the Vcc voltage - Adfive circuit for connecting a power MOSFET directly - Output peak current: Source current -500mA, sink current +1A. - Pulse-by-pulse overcurrent restriction function - Overload protection function (latch or nor-latch mode selectable) - Output ON-OFF function by extemal signal - Latch-mode overvoltage shutdown function - Undervoltage lockout function (16.5V ON/9V OFF) - Reference voltage output (5V) - &pin package (DIP/SOP) 3. Outline SOP-8 (suffix : N) DIP-8 (suffix : P) 8 s 2. 18 £0.08 8 . 5 hHeagqa nda dad! GA « ; & : ° # LPN Tl bd 8 1 sss03 4 HHHSeE + Beas r o=e neth 1se 3 ia WA Ape = i TAIT 8 Yororiot aes fos 201 +O 95a yo
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- Block diagram rage cee = Ss } iB | tet! ca reek ;* iB [aap 5. Pin assignment [ pin [symbot] function | osctpfon [1 [RT| Oscttortmingresistor | Setingosalotonirequeny id | 2 [FB |Feedback | Inputcof PWMoomparator [3 [1s | Overourentsetecion | Input overcurentiniingiindion =| [4 [ono [oon iG SCSC*d [5 [our [out ——=—SSSS~=*dC Opto cinving power MOSFET [6 [vec |Powersivey —SSS~d Powers SCS $$ CUmr
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- Ratings and Characteristics Current characteristics; “+” is sink current and “-" is source current (1) Absolute maximum ratings Supply Low impedance source vcc1 Vv Voltage (CC>15mA) (ICC<15mA) OUT pi peak Gent [Sek canek [OC [Source curent | OH PST | 1S pin input voltage TIS 03 to 50 | [REF pin source current TIER [0 mA | CS pin sink cument CS ma Total power dissipation (Ta=25°C) | P| ‘800 (DIP-8) 400 (SOP-8) 400mw (SOP) 800mW (DIP) as = SI -30 25 85 125 Ambiance temperature Ta [°C] (2) Recommended operating conditions [item Symbol Tin, tmx nit] REF-GND capacito [Ce fo; [oar aT (FB>1.; teres ee [= at lightioad mode _(FB<1.;
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(3) Electrical characteristics (VCC=18V,RT=47kQ, Ta=25°C, unless otherwise noted) Reference voltage section (REF) [tem Symbol Condition MIN, [TP | MAX. [Unit] [Reference voltage | REF [Te2erc 45 T5.00 | 525 Tv | eee Pere ee ine_regulation) eee | ~ ee |= TT oad regulation) VCC=18V ir PPP Na femperature_stabil Oscillator section (RT) [tem Symbol [Condition MIN. TYP MAX. Unit] i (Voltage stabil Pease PE emperature_stabili Pulse width modulation circuit section [tem Symbol Condition MIN. [TYP MAX. Unit] [FB pin source curent_ [FB __—[vre=ov 985-750-615 | A FB p | VTHFBM_| Duty cycle=DMAX || 240 TV [Maximum duty cycle | MAX [rB=25v_ Ts 04 Reducing oscillation frequency section (FB) [tem Symbol Condition MIN, TYP. MAX Unit _] FB pin Input threshold voltage | VTHFBS [TT tte [Frequency reduction | KS1_ FB=1toVto1tsv [te kHz ree eet * TT equenc) Overcurrent limiting circuit section (IS) tem Symbol Condition MIN, Typ [MAX] Unit iia il = IS _pir FA3647P/N -170 a ee ee FA3641N/P FA3647P/N Soft start circuit section (CS) (tem Symbol [Condition MIN. TYP MAX. Unit_] reat Hreshoid wonoge |; muse | Buy arse=oe 5} oss | 03 {| __f v1 (CS pin) [-vrcsm | Duty cycle=DMAX 24g |v Output ON/OFF control circuit section (CS) fo tem Symbol Condition MIN, TTP MAX Unit] [Source curent_(CS pin) [| 'socs | ves=ov, T=25C J 40 65 90 [AY ee a men [See | TO threshold voltage T25°C am Tee [see TT TE25°C 2s MLE
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Latch-mode cutoff circuit section (CS) [tem Symbol] Condition MINS TyP MAX. Unit] Sink current (CS pin) VCS=6.5V, VFB=1V | > | * | uA Ti=25°C VTHCSF | ON — OFF V Cutoff threshold voltage TE25°C a a TE25°C VHS [Oo Overload cutoff circuit section (FB) [item Symbol Condition MIN, TYP. [MAX] Unit] Cutoff-state threshold VIHFB 3.0 Vv Overvoltage cutoff circuit section (VCC) [item Symbol [Condition MIN, TTP MAX. Unit] pave pepe eee ICC p [Charge _current_ (CS pin) | tsocs2_[ves=6sv_ 05 09 4 mA] Undervoltage Lockout circuit section (VCC) [item Symbol Condition MIN, [TYP [MAX Unit __] [OFF-1o-ON threshold voltage | VCCON | Te25°c 55 6s 175 TV [ON-to-OFF threshold voltage | vCCOFF | Tj=25°C 8s 90 Tt00 TV [Hysteresis votage | VHS | Tasca 75 82 VT Output circuit section (OUT) [item Symbol Condition MIN. TTP MAX] Unit_] pom owner | ‘ vec=18v IRisetme Tt OUT=1000pF TCs [Fall ime Tt uT=1000pF_ ts Supply current (VCC) [item Symbol Condition Mins [typ MAX Unit] [Standby curent | tccsTB | Vcc=14v a |Starting-up current ICCST_|_VCC=start threshold p20 puwsmvom | fem tT | supply current |OFF-state supply current | ICCOF__ | vec=17v, cs=ov_ TT t00 fT [Cutoft-state supply curent_ [icc vec=t0v_ as 00]
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7.Characteristics curves Current characteristics; “+” is sink current and “-" is source current {Oscitation frequency (fosc) vs. supply voRage i} timing resistor resistanece(Rt) 105 1000 104 a | oe oe ee ee ee | PEER 103 HENS HHH ee EN | zm | [
2 LONE ses
8 EE EHH ERE SEE 2 99 |
6 ERNE rf
Peedi paseasis, amen ee | a a | 7 | PTE ETT OuT=No load i me TT CU Leemry Fe=15V0 | ‘0 0s | [| 1 10 100 1000 10 15 20 25 30 Rt(kQ) Vee (V) junction temperature (TD, 105 ' | REATKQ | 104 |- FB=25V — 08 | a. ae et po SE § 100 | 0.4 | a | i. > o? oe; a | tt 7 0 -50 0 50 100 150 10 15 20 25 30 Tj (ec) Voo(V) {Supply current (icc) vs. supply voltage (vea)} ‘Supply curent (Jec) vs. mode |Nnction temperature (T)) St es ns em Operating mode. 1.95 1.95 _ 19 H | i 1.85 NS FB=0v FB=0V.
175 L 175
10 6 20 2s 30 -50 0 50 100 150 Vec(V) Tj (*c)
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Supply current (lec) vs.supply voltage vee] ‘Supply current (icc) vs.supply voltage (Vcc)| Latch mode Latch mode 200 . 3000 -—— + i 160 2500 | —— i 7 | = 120 | = i 2 2 = | = 1500 (- [— | 8 8 i 2 nn 3 | | 0 | | | 0 i) 10 12 1“ 16 18 20 10 15 20 25 30 Vee(V) Veo (¥) ‘Supply current (lec) vs.supply votage (Veo) {Supply current (lec) vs.supply votage (veei] OFF mode OFF mode 200 3000 160 2500 1 we 120 - | es | 3 i | 8 | zy st fj) 8 | 1000 — _ | | / “ | | 500 | | 0 4 0 10 12 “ 16 18 20 10 15 20 25 30 Veo(¥) Veo (¥) UVLO OFF-to-ON threshold voage (Vec on) vs. [UVLO ON+o-OFF threshold voltage (Vcc off) vs.| junction temperature (T)) Junction temperature (T) 7 9.2 = “ gee q z PN | = Eo ™ 8 8 | 3 ies 8 ~_| 8.9 + | —_— 16.2 j | | I | 16 8.8 -50 ° 50 100 150 -50 f) 50 100 150 Tico) T)Ce)
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——— ees CS terminal current (ics) vs. CS terminal voltage (ves)] CS terminal current (Ics) vs. CS terminal voRage (ves)] 29 pon _ - 80 4-17} 15 a ce — 40 — = po | | | | | 2 | | | 2 | 0 | ' 10 | + ! } 0 t “10 10 kK | 0 2 4 6 8 10 12 0 2 4 6 8 10 12 Ves (¥) Ves (v) CS terminal charge current (Ichg) vs. FB teminal source current (FB) vs. junction temperature (T) FB terminal vottage (VFB) 5 0 > 1 cse0v | | 100 Z| { i -200 | i . PoP | = aa | | | 600 ~ | i ~700 a oft | | [| -50 0 50 100 150 0 1 2 3 4 5 TiC) VFB(V) 1S(+) terminal current (IS(+)) vs. S(-) terminal current (IS(-)) vs.| 1S(+) terminal vatage (VIS(+)) 'S(_ terminal votage (VES\\-)) FA3641 FA3647 ) 1 5 | aanee 0.1 ; | + A g i Ae oe ——— Z-1o | 2 | 2 1 | ay “0.3 } | | 20 0.4 25 0 05 1 1.5 2 25 3 0.5 0 O5 1 1.5 2 2.5 3 VIS(+) W) VIS(-) W) "1 SBUeEerTRIG
- Description of each circuit 100% (1) Oscillator (fixed frequency) The oscillator generates a triangular waveform by charging and ~ iN discharging the built-in capacitor. A desired oscillation frequency 2 { Duty cycle=10% can be set by the value of the resistor connected to the RT pin g i 'y cycle= (Figure 1). s i = L- Duty cycle=0% g i 6 i i L] rt i ‘ FB pin voltage Fig.1 Oscillator Fig.3 Oscillation frequency ‘The built-in capacitor voltage oscillates between about 3V and 1V, The frequency reduction rate (46%) can be adjusted from the with almost the same charging and discharging gradients (Figure 2). outside. (See Section 9, "Design advice," for more information.) You can set the desired oscillation frequency by changing the gradients using the resistor connected to the RT pin. (Large Rt = low frequency, small Rt = high frequency) The oscillation (3) PWM comparator frequency is automatically lowered when output duty cycle is small (FB < about 1.18V) in light load mode. For more information, see The PWM comparator has four inputs as shown in Figure 4. item (2), "Reducing oscillation frequency circuit in light4+oad mode’ Oscillator output © is compared with CS pin voltage @, FB pin _ voltage ®, and DT voltage ©. The lowest of three inputs @, @, 3v Rt=small Rt=Large and @ has priority and is compared with output ©. While the —~. 4 voltage is lower than the oscillator output, the comparator output is fo \\i., o ., high. While the voltage is higher than the oscillator output, the Vv fe ae PWM comparator output is low (see figure 5). The IC OUT pin _ sf voltage is high while the PWM comparator output is low. When the IC is powered up, CS pin voltage ® controls soft start Oscillator output operation. The output pulse then begins to widen gradually. Fig2 During normal operation, the output pulse width is determined within the maximum duty cycle (70%) set by DT voltage ® under ‘The relationship between Rt and the fixed oscillation frequency is the condition set by FB pin voltage @, to stabilize the output fo kHz} ~ 4880 ay ® DT voltage Rt+14 @ FB pin voltage fo @ oscillator output Where fo is the fixed frequency [kHz] and Rt is timing resistance output [ko]. Fig The oscillator waveform cannot be observed from the outside because a pin for this purpose is not provided. © FB pin voltage (4.0V) ‘The oscillator output is connected to a PWM comparator. The RT pin is 2.5V DC in normal fixed frequency operation mode. © oscillator output When the frequency is lowered, the voltage also decreases linearly to about 1V. @ DT voltage (2) Reducing oscillation frequency circuit in light- —_ cs pin voltage | | i To reduce the loss of the power supply in standby mode, this IC PWM comparator | has a feature that automatically lowers the oscillation frequency output when the load is light. When the load is light, with the result that the IC output pulse width narrows below about 10% and the FB pin voltage decreases below Fig.5 PWM comparator timing chart about 1.18, the oscillation frequency begins to decreases linearly until the output pulse width becomes 0. When the output pulse width is 0, the oscillation frequency is about 46% of normal fixed frequency. (Figure 3). Even while the oscillation frequency is decreasing, the built-in capacitor voltage oscillates between about 3V and 1V.
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——— (4) CS pin circuit (i) Soft start function As shown in Figure 6, capacitor Cs is connected to the CS pin. Figure 8 shows the soft start circuit’ Figure 9 is a soft-start The CS pin voltage varies depending on the charging voltage of operation timing chart. The CS pin is connected to capacitor Cs. this capacitor Cs. When the power is tumed on, the constant When the power is tumed on, the constant current source (6.5,1A) ‘current source (6.51A) begins to charge capacitor. Accordingly, begins to charge the capacitor. As shown in the timing chart, the the CS pin voltage rises as shown in Figure 7. The CS pin voltage — CS pin voltage rises slowly in accordance with the capacitor Cs is connected to the PWM comparator, which is characterized to charging current. The CS pin is also connected to the IC intemal make output based on the lowest of input voltages. The device © PWM comparator, which has such characteristics that the voltage enters soft-start mode while the CS pin voltage is between 1.0V _ is determined to output on the basis of the lowest of input voltages. and 2.4V. During normal operation, the CS pin is clamped at 4.0V The comparator output pulse slowly widens to cause a soft start as by intemal zener diode. shown in the timing chart. The soft start period can be approximately estimated by the period Cs vee ts, from the time the IC is activated to the time the output pulse Files width widens to 30%. The period is given by the following [pent exation: osznosev] | Of <P 1 [eta rs ° REF] a: Where Css the soft start capacitor [11F] Tes | Cs i 3V U.V.L.O. = owas or +t Pee PWM ? BS 3 FB Output [ ose } circuit 6.5pA PWM © @ Output RT FB >> circuit Fig.6 CS pin circuit = asf aa RT > Fig.8 Soft-start circuit s Shutdown FB pin voltage s ae an . Oscillator output to Momentary overload or iad / (0168 0.82) nen overload or overvoltage CS pin voltage f Vv f N. fl A overvoltage i i nena o}-—/ soft start eee = — Time t | Ul | { i i OFF mode i i Po obi ue Fig.7 CS pin waveform OUT pin voltage If the output voltage drops due to an overload and the FB voltage Fig.9 Soft-start timing chart rises to 3V or more, the clamp voltage 4.0V is canceled and the CS. pin voltage rises to 9.5V. The CS pin is also connected to latch comparator C2. If the CS pin voltage rises to 8.5V or more, 7 a comparator C2 toggles to tum off the 5V REF circuit, thereby {li Overload shutdown function ‘shutting the output down. ‘Since the CS pin is also connected to Figure 10 the circuit, and Figure 11 is a comparator C1, the SV REF circuit can be tured off to shut the f10t srs Overload shutdow 4 ‘output down by dropping the CS pin voltage below 0.68V. In this "Ing illustrates overload shutdown operation. way, comparator C1 can be used for output on-off control. , As explained above, the CS pin can be used for soft-start, overload _f the output voltage drops due to an overioad or short circuit, the output shutdown and output on-off control by varying the FB pin output voltage rises. if the FB pin voltage exceeds the ‘ ntrol by varying the voltage. reference voltage (3.0) of comparator C3, the output of comparator Further deta onthe above ree mejor funcons of the CS pn are C3 goes low totum off the switch, - With the switch off the CS pin below. voltage clamped at 4.0V by zener diode in normal operation is unclamped, and the constant current source (6.5A) begins to charge capacitor Cs again and the CS pin voltage rises. When
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the CS pin voltage exceeds the reference voltage (8.5V) of to tum the SV REF circuit. This shuts the output down. The IC ‘comparator C2, the output of comparator C2 toggies to tum off the enters output off (iow voltage) state. Required IC current 5V REF circuit. The IC then enters the latched mode and shuts — consumption during shutdown is 100uA (typ) (Vcc = 17V). This down the output. IC current consumption for shutdown is 45:A current must be supplied through the startup resistor. The IC goes (typ) (Vcc = 10V). This current must be supplied through the on when the CS pin is opened and the CS pin voltage exceeds startup resistor. The IC enters output off (low voltage) state. 0.82V (typ). This tums on the 5V REF circuit and results in The overload shutdown operation can be reset by lowering the automatic soft start. The power supply then restarts operation. ‘supply voltage Vcc to below the OFF threshold voltage (9.0V) or forcing the CS pin voltage below 7.9V. ; ; _ ; ON/OFF control of3-K Cs ‘The period t,, from the time the output is short-circuited to the time J les vec the output circuit goes off is given by the following equation: 1 @) 0.82++0.68V| Where Cs is the soft start capacitor {uF] REF ag—C 5V REF When you want to disable the overload shutdown function, see item (10) in Section 9, * Design advice. * B5OTN. UVLO. Cs T |es vec o—® ® SS 0.82++0.68V FB Output | ol [osc | circuit Of <1 Poeun REF| a: G) 5V REF << RT 8.5-7.9V i 3v UV.LO. Fig.12 Extemal output ON/OFFcontrol circuit + p [> PWM CS pin voltage(4V)- © > Oscillator output FB Output [ ose | circuit DT voltage © FB pin voltage RT ‘Comparator C1 reference voltage Fig.10 Overload shutdown circuit (0.82V) : 7 4 H Comparator C2 es OUT pin outpur i reference voltage t | (8.5V) Hy FB pin voltage 7 REF pin voltage a CS pin voltage (4V) —m — A ALA _A ON mode OFF mode RT vollage avant) Oscillator output \\7 Fig.13 Output ON/OFF contro! circuit timing chart Out pin voltage . i (5) Overcurrent limiting circuit ON - The overcurrent limiting circuit detects the peak value of every drain REF pin voltage -- i current pulse (pulse by pulse method) of the main switching Overload detection MOSFET to limit the overcurrent. The detection threshold voltage —> is +0.235V for FA3641 or -0.17V for FA3647 with respect to the Overload shutdown —_ ground as shown in Figure 14. The drain current of the MOSFET is converted to voltage by Fig.11 Overload shutdown timing chart resistor R, and fed to the IS pin of the IC. If the voltage exceeds the reference voltage +0.235V (FA3641) or -0.17V (FA3647) of (ii) Output on-off control function comparator C4, comparator C4 works to set fip-fop output Q to The IC can be tumed on or off via an extemal signal applied to the high. The output is immediately tuned off to shut off the current. CS pin. Figure 12 shows the output on-off control circuit, and Flip-fop output Q is reset on the next cycle to tum on the output Figure 13 is a timing chart. again. This operation is repeated to limit the overcurrent. If the overcurrent limiting circuit malfunctions due to noise, place an i Pp RC filter between the IS pin and MOSFET as shown in Figure 14. The IC is tumed off when the CS pin voltage is extemally made to * i ~ : ~ y . hic (See (14) in Section 9," Design Advice.") drop below 0.68V (typ). The output of comparator C1 goes high Figure 15 sa timing chart that il a ions.
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10V). This current must be supplied through the startup resistor. FA3641 ‘The overvoltage shutdown operation can be reset by lowering the supply voltage to below 9.0V or forcing the CS pin voltage below tH [osc] uv.Lo. TV. cs (When you want to enable Voc overvoltage shutdown at a desired Sen > => our voltage, see item (6) in Section 9, " Design advice.” Oscillator ‘Output y ocP Fa circut 5 ve [4 0.24V (2 5 L FF (| Rs 0 4 q @) @) Ise) c GND - Pls fe K R tt — <¢ Oe aaa 15.5V, re pag SREY oom f= FA3647 Ene Bes s 15.5V OV REF <4 |lSr4 [osc] uv.Lo. 5 « we wg bee | EE Spin = l) ae >> sik “et L Oscillator ‘Output FB@ . ocp circuit | ye Omax Ba => iar] ov [> eI FF [| @) @ q fr SO - Fig.16 Overvoltage shutdown circuit ‘Comparator C — reference voltage on (8.5V) | Fig.14 Overcurrent limiting circuit : CS pin voltage / H CS pin voltage (4¥) DT voltage _A FB pin vott DT pin voltage pin votoge FB pin voltage Oscillator output ro o onto unt” po ouTpin ouput" ai OUT pin output | I Comparatorc4 ) * ' : REF pin voltage dl reference voltage | | i FA3641:+0.24V 7 Son Shutdown FA3647:-0.17V ao r ro Overvoltage detection 1S pin voltage. i | Fig.17 Overvoltage shutdown timing chart REF pin voltage “ H T Overcurrent limiting (7) Undervoltage lockout circuit (U.V.L.O.) Fig.15 Overcurrent timing chart The IC incorporates a circuit that prevents the IC from malfunctioning when the supply voltage drops. When the supply, ee voltage is raised from OV, the IC starts operation with Voc = 16.5V (6) Vcc overvoltage protection circuit (yp). If the supply voltage drops, the output is shut down when danas by ovanehene rene 16 shone the ceontane routes She OUtan Cope nee Pekout circu damage by overvoltage. Figure 16 shows overvoltage protection circuit. Figure 17 is a timing chart that illustrates Overvoltage is detected if the supply voltage Ver rises to 32V (loc = (8) Output circuit ihr esiebane allan tees aerier The The IC contains push-pull output stage and can directly drive the source (0.9mA) raises the CS pin voltage. When the CS pin Bik urent of 1A atv! & poutce cuvert Of OG i te chua voltage exceeds 8.5V, the output of comparator C2 goes high to ‘operation st when the undervoltage lockout circuit operate, the tum off the 5V REF circuit. The IC then enters the laiched mode G(s pin vottage goes low to shut down the MOSFET ’ and the IC output is put in the off (low voltage) state. When goes zg latched mode, the IC current consumption is 45yA (typ) (Vcc =
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- Design advice (2) Deciding the startup circuit (1) Extemally setting the oscillation frequency in These ICs, which uses CMOS process, consume less current, and the light-load mode therefore can use larger startup resistance than the conventional bipolar type of IC. As explained in (2) in Section 8, "Description of Each Circuit," the IC To decide the startup resistance, the following conditions must be has a function that automatically lowers the oscillation frequency _ satisfied: when the load is light to reduce the loss of the power supply in (a) The ICis started when the power is tumed on. ‘standby mode. The oscillation frequency goes down to about (b) The IC consumption current is supplied during latch mode 46% without adjustment by extemal circuit. operation to maintain the latch state. (©) The IC consumption current is supplied during the off state To further lower the frequency below 46%, connect adjustment under the on-off function to maintain the off state. resistor Rr between the RT and the REF pins as shown in Figure 18. Then the fixed frequency determined by Rt also falls. However, these are the minimum conditions for using the IC. The startup time required for a power supply must also be decided on. d (i) Connecting a startup resistor before rectification (AC line) ie | When the startup resistor is connected before rectification (AC line) as shown in Figure 19, the voltage applied to the startup resistor 5 {oe . forms a half-wave rectified waveform of the AC input voltage. [] Rt Startup resistor R1 must satisfy the three equations shown below. Select a smaller-side value for R1 in consideration of the + temperature characteristics. (2) To supply startup current 301A at ON threshold voltage 17.5V Fig.18 Oscillator circut (max. of UVLO: The relationship between the extemal resistance and oscillation p-mahiehee frequency is outlined below: RUkQ] = 8 — Tg 8) 3.35A-B A-B (b) To supply IC consumption current 100A (max) (Voc = 10V) 4880 2500 in latch mode: RR 4 _ RR 2 yac-10 Rr-Rt Rr—-3.35Rt R1[kQ] = =— sereeeeee(Q) . 01 fo : Fixed frequency [kHz] (©). To supply IC consumption current 200A (max) (Voc = 17V) f, :Minimum frequency in var iable mode [kHz] in the off state under the on-off function: Rt: Timing resistor [kQ] 2 ae—17 Rr: Adjustment resistor [kQ] RA[ko] = seseeeeee(10) anf pt 02 ° ' Where; Rt: Startup resistance [kQ] Select Rt and Rr so that the relationship between the two satisfies Vac: Effective value of AC input voltage [V] ne tf neither the latch mode operation nor the on-off functions are used, In this method, the supply current to the IC via the start-up resistor * Set the minimum frequency in light4oad mode to 10 kHz or iS stopped when AC input is shut down. Therefore, after latch mode more. ‘operation, shutting the AC input down resets the latch mode in a very short period of time. Failure to keep the above relationship may disturb the operation. Note that the above expressions determine approximate values. Note also that the minimum frequency in lightload mode depends on such conditions as the power supply efficiency. Therefore, check the operation using a practical circuit to make a final decision. (Calculation example) To set the fixed frequency fo = 100kHz and the minimum frequency in light4oad mode to fr = 20kHz, the following can be obtained from ‘expressions (5). Rt ~37.7[kQ] Rr =185.1[kQ] Decrease Rr to permit the frequency to vary in a wider range.
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‘AC INPUT | | a 3 ‘AC INPUT | | a : [] l] K} KI Ay : vee be 02 : wee) © OUT [Js [] rs Fig.19 Startup circuit (1) Fig.20 Startup circuit (2) (ii) Connecting the startup resistor after rectification (3) Determining the Vcc capacitor value (DC fine) To property start the power supply, a certain value is required for the When the startup resistor is connected afer rectification (DC line) capacitor connected to the VCC pin. as shown in Figure 20, the voltage applied to the startup resistor Figure 21 shows the Vcc voltage at start-up when a proper value is becomes the peak value of the AC input voltage. given to the capacitor. Startup resistor R1 must satisfy the three equations shown below. Select a smaller-side value for R1 in consideration of temperature — When the input power is tumed on, the capacitor connected to the characteristics. VCC pin is charged via the startup resistor and the voltage increases. The IC is then in standby state and almost no current (a) To supply startup current 30A at ON threshold voltage 17.5V is consumed. (loc < 2A) (max.) of UVLO: Thereafter, Voc reaches the ON threshold voltage of UVLO and the V2xVac-17.5 IC begins operation. R1[kQ) = =... (11) When the IC begins operation to make output, the IC operates 0.03 based on the voltage from the auxiliary winding. When the IC is . just starting up, however, it takes time for the voltage from the (b) To supply IC consumption current 100A (max) (Voc = 10V) auxiliary winding to rise enough, and Vec drops during this period. in shutdown or OFF mode: J2xVac-10 Determine the Voc capacitor value so that Vcc will not drop down to RQ] = rere (12) the OFF threshold voltage of UVLO during this period. 5 = When the capacitor value is adequate (c) To supply IC consumption current 200A (max.) (Vec = 17V) Vec in the off state under the on-off function: uvLo v2xVac-17 ny aay Aare RA[KQ] = re (18) on Vee must not drop to : UVLO OFF. UVLO . Where; 1 i ey ar aes . fn i i — Auxiliary winding volta Vac: Effective value of AC input voltage [V] fe Kesar wing volage If neither the latch nor the on-off functions are used, only the - Tae expression in (11) needs to be satisfied. In this method, after latch mode operation, smoothing capacitor C1 in the main circuit supplies current to the IC via the startup resistor Fig.21 Vcc voltage at startup with a adequent capacitor even if the AC input is shut down. Therefore, some time must elapse before the latch mode is reset. If the Voc capacitor value is too small, Voc will drop to the OFF threshold voltage of UVLO before the auxiliary winding voltage fises enough. If so, Voc repeatedly goes up and down between the UVLO threshold voltages, and the power supply cannot start up. (Figure 22)
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(6) Overvoltage protection using the VCC pin When the capacitor value is inadequate ve This IC contains an overvoltage protection function detecting the ‘cc Vec voltage using intemal ZD (see item (7) in Section 8, UVLO "Description of each circuit’). If Voc voltage exceed about 32V, ON PITTI the current of 13mA flows through the intemal ZD and the uvto After this protection function operates, the IC continues to consume pin. Mind that total IC loss does not exceed the rating. if the voltage source applied to Vcc pin has relatively high impedance and cannot source the current of 13mA, overvoltage Time t protection function does not operate. But the intemal ZD maintains Fig.22 Vee voltage at startup with a inadequent capacitor «N° Vo" voltage 32V or less and protects the IC. (4) Shortening the startup period (7) Overvottage protection using CS pin Increasing the resistance of the startup resistor to reduce loss These ICs contains the overvoltage protection function detecting prolongs the startup period. Figure 23 shows a circuit for Vee voltage. However, the threshold voltage of the function is fixed. shortening the startup period. The C2 capacitance is decreased Adding some circuit to CS pin enables the overvottage protection to shorten the startup period and, after the IC starts up, power is detecting desired voltage. from C3. supplied () Detecting on secondary side a Figure 25 shows the overvoltage shut down circuit based on the ] D1 pe signal from the secondary side. The optocoupler output transistor 1] KJ is connected between the CS and Vcc pins. When the output . fe 2 voltage is put in the overvoltage state, The optocoupler output vec Hoo os ° transistor goes on to rise the CS pin voltage via resistor R2. © + tL When the CS pin voltage exceeds the reference voltage (8.5V) of = = = comparator C2, the output of the comparator C2 goes high to tum FA3641/47 Off the 5V REF circuit. Accordingly, the IC enters the OFF latch mode and shuts the output down. The IC consumes current 45pA (typ) (Voc = 10V) in latch mode. This current must be ‘supplied via startup resistor R1. Fig.23 startup circuit (3) The overvoitage protection circuit can be reset by lowering the (5) Setting soft start period and OFF | supply wattage Vor to below 9.0V or forcing the CS pin votiage independently In normal operation, the CS pin voltage is clamped by the 4V zener - ; . diode with maximum sink current 501A. Therefore, to raise the Figure 24 shows a circuit for setting the soft start period and OFF —_CS pin voltage to 8.5V or more, 501A or a higher current needs to latch delay independently. In this circuit, capacitance CS be supplied from the optocoupler. Set the current input to the CS determines the soft start period, and capacitance CL determines pin to 1mA or less. the OFF latch detay. ; — . , If the overload shutdown or overvoltage shutdown functions raise Vin | | 4 a 2 EF | Vout the CS pin voltage to around 5V, zener diode Zn becomes |. | 7 9 conductive to charge capacitor CL. The OFF latch delay can be | thus prolonged by capacitance CL. [Jn A — A cL Pc Cs ZY ws | ¢ a ‘) cs () ete YS gs FA3641/47 - Ory Paw Fig.25 Overvoltage shutdown circuit (1) Fig.24 Independent setting of soft start period and OFF latch delay
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(ii) Detecting on primary side (detecting Vcc voltage) (9) REF characteristics To attain overvoltage protection, the CS pin voltage is forcibly raised __ If noise is applied to the VCC pin from the outside, it may appear at from outside the IC until it exceeds the reference voltage (8.5V) of the REF pin without attenuation depending on the noise frequency. the intemal comparator C2. When the reference voltage is The noise causes no problems in normal IC operation, but must be exceeded, the IC enters latch mode and shuts the output down. taken into consideration when the REF voltage is used for an Connect a zener diode (ZD) and resistor between the Vcc and CS —_ extemal circuit. _ If the noise appearing at the REF pin causes any pins as shown in Figure 26. When the Voc voltage exceeds about _ problems, use the REF pin as shown in Figure 29. 2D voltage + 8.5V,the IC enter the OFF latch mode and shut the output down. If Vcc remains high even after shutdown and To external circuit current is input to the CS pin, set the current to 1mA or lower. REF J Set the zener voltage of the ZD connected to the CS pin higher cref L,0- 47uF than the UVLO ON threshold voltage. Startup is disabled below pu R4 this voltage. 1 L332 R220 - ” cs Fig.29 REF pin circuit vec (10) Simple voltage control on the primary side ; _ In a flyback type power supply, the output voltages of the power Fig.26 Overvottage shutdown circuit (2) supply and auxiliary winding voltage are almost proportional to the number of winding tums of the transformer. This characteristic _ , can be used in the circuit shown in Figure 30, where the output Figure 27 shows another circuit for enabling latch mode shutdown r * by detecting a desired Voc voltage using the CS pin. In this circuit, bianlrsehdid nade constant by detecting the voltage of the ‘overvoltage shutdown works when the Voc voltage is about the } same as the ZD voltage. However, this is an easy output voltage control method, and the For this circuit also, use a ZD voltage higher than the UVLO ON output vol wane or roe ctl Corotaly bo O86 te SFB pin wohage threshold voltage. Set the current flowing into the CS pin to IMA muct fall below 0.95V and R5 must be set below about 9600 from or - the characteristics of the FB pin source current. When using this _ method, also keep in mind the characteristics of REF in (8). la! veut d Ef vec | [ro Azo cs ® s Cs = L ra? omni stron et) c—= O—O (8) Feedback pin circuit veo REF 4 - kon in whi FA3641/47 G Figure 28 gives an example of connection in which a feedback re Ui signal is input to the FB pin. oT 3 If this circuit causes power supply instability, connect R3 and C4 as shown in Figure 28 to decrease the frequency gain. Set R3 . between several tens of ohms to several kiloohms and C4 between Fig.30 Simple voltage control circuit several thousand picofarads to one microfarad. Be especially careful in light load mode, in which the frequency drops, thereby increasing the probabilty of power supply instablity being triggered. (11) Disabling the overload shutdown function Vout As shown in Figure 31, connect an 8.2kQ resistor R6 between the FB pin and the ground. The FB pin voltage then does not rise sufficiently high to reach the shutdown threshold voltage when an overload occurs so that IC does not enter OFF latch mode. Even with this connection, the overvoitage shutdown function is available. ease 4 Since resistor R6 limits the upper voltage of the FB pin, the ® Rs pcr maximum duty cycle may be limited to about 65%, if a 5% precision 6 L resistor is used. To not limit the maximum duty cycle, use a 2% or []rs C Pot better-precision resistor for R6. st Fig.28 FB pin circuit
19 ELECTRIC
(14) Preventing malfunction caused by noise FA3641/47 The IS pin for overcurrent limiting function detects the MOSFET FB GND current converted to the voltage. The parasitic capacitor and @) @ inductor of the MOSFET, transformer, wiring, etc. cause a noise in switching operation. If this switching noise causes a malfunction of ‘overcurrent limiting function, insert the RC filter into IS pin as shown [] Fe R3 in Figure 14. Also, connect a noise prevention capacitor (0.11F or more) to the REF pin that outputs the reference voltage for each ro component. +- + - Fig.31 Disabling overload shutdown function (15) Preventing matfunction caused by negative voltage applied to a pin (12) Polarities for overcurrent detecting and their large . is applied to each IC pin, a ae characteristics element in the IC may operate and cause matfunction. | Be careful not o allow the voltage to each pin to drop below -0.3V. The FA3641 uses postive polary detection for overcurent ming POU0 Sata wolloe 2ORIEN S caen to oes the (number 3 pin of IS terminal) and the FA3647 uses negative — MOSFET tums off may be applied to the OUT pin via the parasitic Polarity detection. The characteristics of positive and negative Co citance of the MOSFET, causing the negative voltage to be Polarity detection are summarized below. Select one in -ooied to the OUT pin. If the voltage falls below -0.3V, add a accordance with the circuit used. (See item (5) in Section 8, Schottky diode between the OUT pin and the ground. The “Description of each circuit”) forward votage of the Schottky diode can suppress the voltage Positive | - Wing is easy because the ground can be] PPliedito the OUT pin. detection | shared by the main circut and IC peripherals. Use the low forward voltage of the Schottky diode. Similarly, be (FA3641) |- It is easy to correct the overload detecting ‘ 7 ‘ current, which is used to , careful not to allow the voltages at other pin drop below -0.3V. against the input voltage. i = The MOSFET drive current does not flow to OUT Geeson | the curent detocion resistor and therefore t FA3641/47 GO F (FA3647) | hardly affects overcurrent detection. @ nD ZX SBD (13) Correcting overioad detection current (FA3641 only) If the power supply output is overload, the IC overcurrent limiting Fig.33 Protection of OUT pin against the negativ voltage function restricts the output power and the overload shutdown function stops the IC. The output current when an overload (16) Gate circuit configuration occurs varies depending on the input voltage; the higher the input voltage, the more the overload detection current may increase. To adjust switching speeds or prevent oscillation at gate terminals, 1f any problems occur as a result of the appearance of this resistors are normally inserted between the power MOSFET gate symptom, connect resistor R8 between current detection resistor terminal to be driven and the OUT pin ofthe IC. You may prefer to Rs and the IS (+) terminal and add resistor R7 for correction 2s decide on the drive current independently, to tum the MOSFET on shown in Figure 32. The standard resistance of R8 is several and off. If so, connect the MOSFET gate terminal to the OUT pin hundred ohms and that of R7 is from several hundred kiloohms to _ of the IC as shown in Figure 34. several megohms. ; In the circuit shown in Figure 34, Rg1 and Rg2 restrict the current Note that the above correction slightly lowers the output current —_ when the MOSFET is tumed on, and only Rg1 restricts the current when overload even where the input voltage is low. This whenitis tumed off. correction is available only for the FA3641 IC that uses positive polarity for overcurrent detection. Rel Re2 bs ia Fa3641/47 @—C 714 ° + 2 / out La ‘AG INPUT ma! = Fig.34 Gate circuit
1 Ik (18) Loss calculation
ve IC loss must be confirmed to use the IC within the ratings. Since it Fas6at OO) is hard to directly measure IC loss, some examples of calculating Is (+) rl approximate IC loss are given below. Rs I L (i) Calculation example 1 Suppose the supply voltage is Voc, IC current consumption is Iccop, Fig.32 Correcting overload detecting current circuit the total gate charge of the power MOSFET is Qg, and the switching frequency is fsw. Total IC loss Pd can be calculated by:
20 SLECTRIG
When gate resistance differs between ON and OFF as shown in This expression calculates an approximate value of Pd, which is a1 Ron Roff_ normally a litle larger than the actual loss. Since various Pa" = 2% VoexGaxfewx! FRO aot Rotel [I conditions such as temperature characteristics apply, thoroughly verify the appropriateness of the calculation under all applicable vec conditions. © Example: . . Ko When Voc = 18V, loop = 2.5mA (max) is obtained from the 71 OUT Rel Rg2 specifications. Suppose Qg = 80nC and fsw = 100kKHz. O—CRO La Pd = 18V x(2.5mA + 80nC x 100kHz) _IEy KI =189mW Oop (i) Calculation example 2 Fig.36 Gate circuit a 5. Example: The IC loss consists of the loss caused by operation of the control . . oe Pas When Vec = 18V, Qg = 80 nC, fsw = 100 kHz, and Rg = 10 Q, the circuit and the loss caused at the output circuit to drive the power . leah MOSFET. typical IC loss is given by: 1) Loss at the control circuit Pdr = 4x18V x80nCx100kHzx(— 82 _,_70_ 2 102+15Q ° 102+72 The loss caused by operation of the IC control circuit is calculated =72.8mW by the supply voltage and IC current consumption. When the = fem ‘supply voltage is Voc and IC current consumption is Iccop, loss Pop at the contro! circuit is: 3) Total loss Pop =Veexlocop ss... (15) The total loss (Pd) of the IC is the sum of the control circuit loss (Pop) and the output circuit loss (Pdr) calculated previously: Example: ‘specifications. The typical IC loss is given by: Pop = 18V x 1.9mA = 34.2mW The standard IC loss under the conditions used in 1) and 2) above are: 2) Loss at the output circuit Pd = Pop + Pdr = 34.2mW + 72.8mW = 107mW The output circuit of the IC is a MOSFET push-pull circuit. When the ON resistances of MOSFETs making up the output circuit are Ron and Roff, the resistances can be determined as shown below based on Vcc = 18V and Tj = 25°C obtained from the output Ron = 150 (typ) Roff = 7Q (typ) vec “|p out Re | : _IK Oar) Fug.35 Output stage When the total gate charge of the power MOSFET is Qg, the switching frequency is fsw, the supply voltage is Voc, and gate resistance is Rg, the loss caused at the IC output circuit is given by:
1 Ron Roff
Par= 5 VeoxQextow( aan *agemaH jo)
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- Application circuit FA3641 gE 2 a 2 £235Q 7" “tae
4 KR gg 83
= Lemme OO —— | 3 ° Vase Re sé 5a Es . gl i gs 20-16¥¥3 8g ot EQS 4 | ct re gs 8g 3g 38 i 49001 ss "8 “8 ° 8019 8G 5 lod, Py S BS 32 Sa cu os Ea ac ek 1" 400z a a
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=e 2 Bese s 32255 SS 8 n . \\ | ge ’ KR ge 3 = Aa zs S= 85 “Ee < a KI | Hee oe | ge °s Le ls | e vad > S o “ aS at = 28 ane ak Es els Agel ie gs 20-16vua 38 2a sa 23 2 #Q5 = “7 [TE | es oe 33 ae 33 sez_| | | sen ox =3 “8 zs 010 Ses boars ae s S BS, 3s ELAR) sa st or L019) ax 3g. < ony et sa Se: Fed uy
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Electrical characteristics of Application circuit (on page 22 and 23) Input power vs. input voltage
0.6 Condition: no-load
cos} ful [04 o Zoo) S02) ee c 0 50 100 150 200 250 300 Input voltage (Vac) 10 Input power vs. output power es ee ee | ee > a eee ee = be o oe RE ll iad F=—+ AC230V = eel
2 SS Ea enn eral
Fe crO0V | emai oy LI il 0.01 0.1 1 10 Output power (W) Oscillation frequency vs. output power = sof 5 70 Fs 60 a 27 50 ! B 20 L oh > tT Oo 10 ; pe 0 10 20 30 40 50 60 70 Output power (W) ——— eS