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1 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e fuji power supply control ic FA7700V/01v application note dec -2000 fuji electric co., ltd. matsumoto factory
2 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e 1.this data book contains the product specifications, characteristics, data, materials, and structures as of dec 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 fail-safe, 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 ? personal equipment ? 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 control 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. warning
3 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e contents page 1. description ??????????????????? 4 2. features ??????????????????? 4 3. outline ??????????????????? 4 4. block diagram ??????????????????? 5 5. pin assignment ??????????????????? 5 6. ratings and characteristics ??????????????????? 6 7. characteristics curves ??????????????????? 9 8. description of each circuit ??????????????????? 13 9. design advice ??????????????????? 17 10. application circuit ??????????????????? 18 note ? parts tolerance and characteristics are not defined in all application described in this data book. when design an actual circuit for a product, you must determine parts tolerances and characteristics for safe and stable operation.
4 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e 1 ? ? ? ? description FA7700V/fa7701v are the pwm type dc to dc converter control ics with 1ch output that can directly drive power mosfets. cmos devices with high breakdown voltage are used in these ics and low power consumption is achieved. these ics have the many functions equivalent to those which our conventional version bipolar ics ? fa76xx series- have,and have merits of output on/off control function,directly driving nch/pch mosfets,low power consumption , higher frequency operation, and less external discrete components. 2 ? ? ? ? features ? ? wide range of supply voltage.: vcc=2.5 to 20v ? ? FA7700V?for boost, flyback converter (maximum output duty cycle is 80%) fa7701v?for buck converter (maximum output duty cycle is 100%) ? ? output stage consist of cmos push-pull circuit, and achieves a high speed switching of external mosfets. (FA7700V: for nch-mosfet driving, fa7701v: for pch-mosfet driving) ? ? high accuracy reference voltage (error amplifier): 0.88v 2% ? ? soft start function. ? ? adjustable built-in timer latch for short-circuit protection. ? ? output on/off control function ? ? less external discrete components needed (2 components less than conventional version of the equivalent products) ? ? low power consumption stand-by current: 40 a(typ.) operating current: 1.2ma(typ.) (including error amplifier output current and oscillator current) ? ? high frequency operation: 50khz to 1mhz ? ? package: tssop-8(thin and small) 3 ? ? ? ? outline units:mm
5 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e 4 ? ? ? ? block diagram 5 ? ? ? ? pin assignment pin no. pin name function 1 rt oscillator timing resistor 2 ref internal bias voltage 3 in(-) error amplifier inverting input 4 fb error amplifier output 5 gnd ground 6 out output for driving switching device 7vccpower supply 8 cs on/off, soft start, timer latched short circuit protection ') ' +' $( *+!$ ? - + ? # ? %," - + ? ?
? ? ?? ?? - + ?
? ? 6>,9?66+?0.5(3 ? ? ? t y ( + $*) # - + ??? '}"% + 2.2v ? ? %," vref - + ??? '}"% ? ? ? t y + +' $( *+!$ ? - + - + ? ?
? ? ?? ?? - + ?
? ? 6>,9?66+?0.5(3 ') ' # ( + $*) # 2.2v
6 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e 6 ? ? ? ? ratings and characteristics (1) absolute maximum ratings item symbol ratings units power supply voltage vcc 20 v ref terminal output current i ref 2ma i sopeak -400(peak) out terminal source current i socont -50(continuos) ma i sipeak +150(peak) out terminal sink current i sicont +50(continuos) ma rt | ref | in | fb terminal voltage v rt v ref v in- v fb +2.5(max.) -0.3(min.) v cs terminal voltage v cs self limiting 5.5(max.) -0.3(min.) v cs terminal sink current i cs 200 a power dissipation pd 250(ta ? 25 ? ) mw operating ambient temperature ta -30 ? +85 ? operating junction temperature tj +125 ? storage temperature t stg -40 ? +150 ? (2) recommended operating conditions item symbol min. typ. max. units supply voltage v cc 2.5 6 18 v dc feedback resistor of error amplifier r nf 100 k
vcc terminal capacitance c vcc 0.1 f ref terminal capacitance c ref 0.047 0.1 1 f cs terminal capacitance c s 0.01 10 f cs terminal sink current i csin 1 (*1) 50 a oscillation frequency f osc 50 1000 khz (*1)lower limit of i csin does not include leak current ?i ! ? for capacitor cs. set a resistor yy ?rcs |"
? connected between vcc terminal and cs terminal to satisfy the following equation. l cc cs l cc i ua v m r i ua v + ? < < + ? 1 5 . 1 ] [ 50 5 . 1
maximum power dissipation curve 0 50 1 00 1 50 200 250 300 -30 0 30 60 90 1 20 1 50 ambient temperature [ ] maximum power dissipation [mw
7 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e (3) electrical characteristics (unless otherwise standard, ta=25 ? ,vcc=6v,r t =22k
) (1)internal bias section (ref terminal voltage) item symbol conditions min. typ. max. units output voltage v ref ref terminal source current i ref = 0ma 2.16 2.23 2.30 v line regulation v line vcc = 2.5 to 20v | i ref = 0ma ? 2 ? 14 mv load regulation v load i ref = 0 to 2ma ? 2 ? 12 mv v tc1 ta = -30 to 25 ?? 0.3 % variation with temperature v tc2 ta = 25 to 85 ?? 0.3 % (2)oscillator section (frequency set by rt terminal ) item symbol conditions min. typ. max. units oscillation frequency f osc r t = 22k
155 185 215 khz line regulation f line vcc = 2.5 to 20v ? 0.1 % f tc1 ta = -30 to 25 ? , 50k to 1mhz ? 2 % variation with temperature f tc2 ta = 25 to 85 ? , 50k to 1mhz ? 3 % (3)error amplifier section (in- terminal , fb terminal item symbol conditions min. typ. max. units reference voltage v b in- terminal, fb terminal :shorted (voltage follower) 0.863 0.880 0.897 + input current i in- -500 +500 na ?v b ? line regulation v bline vcc = 2.5 to 20v ? 1 ? 5 mv v btc1 ta = -30 to 25 ?? 0.3 % ?v b ? variation with temperature v btc2 ta = 25 to 85 ?? 0.3 % open loop gain a vo 70 db unity gain bandwidth f t 1.5 mhz source i ohe fb terminal = v ref - 0.5v -220 -160 -100 a output current sink i ole fb terminal = 0.5v 3 6 12 ma (4)pulse width modulation (pwm) section (fb terminal voltage and duty cycle) item symbol conditions min. typ. max. units fb 0% threshold v fb0 duty cycle = 0% 0.560 0.660 0.760 + fb 50% threshold v fb50 duty cycle = 50% 0.880 + d max1 r t = 100k
, 5 50khz 85 90 95 % d max2 r t = 22k
, 5 185khz 83 88 93 % fa7700 d max3 r t = 3k
, 5 1mhz 80 86 92 % maximum duty cycle fa770 1 d max 100 % (5)under voltage lock-out section (vcc terminal voltage) item symbol conditions min. typ. max. units on threshold v ccon 2.07 2.30 + off threshold v ccof 1.60 1.93 + hysteresis voltage v cchy 0.04 0.14 0.24 + ta = -30 to 25 ? 0.2 mv/ ? variation with temperature v cchy ta = 25 to 85 ? 0.2 mv/ ?
8 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e (6)on/off section (cs terminal voltage) item symbol conditions min. typ. max. units on/off threshold v onof 0.150 0.300 0.450 + threshold variation with temperature v ontc ta = -30 to 85 ? +0.5 mv/ ? (7)soft start section (cs terminal voltage) item symbol conditions min. typ. max. units threshold voltage 1 v cs0 duty cycle = 0% 0.560 0.660 0.760 + threshold voltage 2 v cs50 duty cycle = 50% 0.880 + (8)timer latched short circuit protection section (fb terminal, cs terminal) item symbol conditions min. typ. max. units short detection threshold voltage v fbth fb terminal voltage 1.350 1.500 1.650 + latched mode threshold voltage v csth cs terminal voltage 2.050 2.200 2.350 + latched mode reset voltage v csre cs terminal voltage 1.700 2.030 2.300 + latched mode hysteresis v cshy cs terminal voltage 50 170 350 mv v cscl1 fb terminal<1.35v cs sink current = +1 a 1.400 1.500 1.600 + ( terminal clamped voltage v cscl2 fb terminal>1.65v cs sink current = +150 a 4.500 5.500 6.500 + (9)output stage section (out terminal) item symbol conditions min. typ. max. units r onh vcc = 6v, source current = -50 < a 10 20
high side on resistance r onh vcc = 2.5v,source current = -50 < a 18 36
r onl vcc = 6v, y sink current = +50 < a 510
low side on resistance r onl vcc = 2.5v, sink current = +50 < a 510
fa7700 330pf load to gnd terminal 20 ns rise time fa770 1 tr 330pf load to vcc terminal 25 ns fa7700 330pf load to gnd terminal 45 ns fall time fa770 1 tf 330pf load to vcc terminal 40 ns (10)overall section (supply current to vcc terminal) item symbol conditions min. typ. max. units off mode supply current i ccst1 cs terminal=0v 40 100 a i cc0 duty cycle = 0%, out:open in- =0v, fb:open 0.9 1.5 ma operating mode supply current i cc1 duty cycle = 50%, out:open in-, fb:shorted 1.2 2.0 ma latched mode supply current i cclat cs terminal >2.35v in- = 0v, fb:open 0.9 1.5 ma
9 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e 7 ? ? ? ? characteristics curve timing resistor vs. oscillation frequency 1 0 1 00 1 000 1 0000 11 0 1 00 timing resistor r t k ? oscillation frequency khz oscillation frequency vs. ambient temperature -5 -4 -3 -2 - 1 0 1 2 3 4 5 -40 -20 0 20 40 60 80 1 00 ambient temperature ta [ ] oscillation frequency variation[ ] fosc= 1 mhz fosc= 1 85khz fosc=50 khz fb terminal voltage vs. duty cycle 0 1 0 20 30 40 50 60 70 80 90 1 00 0.5 0.7 0.9 1 . 11 .3 fb terminal voltage [v] duty cycle [ ] fa7700 fosc= 1 mhz fosc= 1 85khz cs terminal voltage vs. duty cycle 0 1 0 20 30 40 50 60 70 80 90 1 00 0.5 0.7 0.9 1 . 11 .3 cs terminal voltage [v] duty cycle [ ] fa7700 fosc 1 mhz fosc= 1 85khz fb terminal voltage vs. duty cycle 0 1 0 20 30 40 50 60 70 80 90 1 00 0.5 0.7 0.9 1 . 11 .3 fb terminal voltage [v] duty cycle [ ] fa770 1 fosc= 1 mhz fosc= 1 85khz cs terminal voltage vs. duty cycle 0 1 0 20 30 40 50 60 70 80 90 1 00 0.5 0.7 0.9 1 . 11 .3 cs terminal voltage [v] duty cycle [ ] fa770 1 fosc 1 mhz fosc= 1 85khz
10 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e maximum duty cycle vs. ambient temperature 80 82 84 86 88 90 92 94 -40 -20 0 20 40 60 80 1 00 ambient temperature ta [ ] maximum duty cycle [ ] fa7700 fosc= 1 mhz fosc= 1 85khz fosc=50 khz error amp. reference voltage vs. ambient temperature 0.86 0.87 0.88 0.89 0.90 -40 -20 0 20 40 60 80 1 00 ambient temperature ta [ ] reference voltage [v] internal bias voltage vs. ambient temperature 2. 1 8 2.20 2.22 2.24 2.26 2.28 -40-200 20406080 1 00 ambient temperature ta [ ] internal bias voltage [v] cs terminal on/off threshold vs. ambient temperature 0. 1 5 0.20 0.25 0.30 0.35 0.40 -40 -20 0 20 40 60 80 1 00 amient temperature ta [ ] cs terminal on/off threshold [v] under voltage lock-out vs. ambient temperature 1 .80 1 .85 1 .90 1 .95 2.00 2.05 2. 1 0 2. 1 5 2.20 -40-200 20406080 1 00 ambient temperatureta [ ] vcc terminal on/off threshold v ccon v ccoff cs terminal voltage vs.cs terminal sink current 0 20 40 60 80 1 00 1 20 1 40 1 60 1 80 200 0 1 234567 cs terminal voltage [v] cs terminal sink current [ua] fb< 1 .35v fb> 1 .65v ta=-30 ta=25 ta=85
11 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e off mode supply current vs. temperature 30 35 40 45 50 55 60 -40-200 20406080 1 00 temperature ta [ ] off mode supply current [ua] cs=0v vcc=20v vcc= 6v operating mode supply current vs. temperature 0.6 0.7 0.8 0.9 1 .0 1 . 1 1 .2 1 .3 1 .4 1 .5 -40 -20 0 20 40 60 80 1 00 temperature ta [ ] operating mode supply current [ma] rt=22k vcc=20v (duty=50%) vcc= 6v (duty=50%) vcc= 6v (duty=0%) latched mode supply current vs. temperature 0.70 0.75 0.80 0.85 0.90 0.95 1 .00 -40 -20 0 20 40 60 80 1 00 temperature ta [ ] latched mode supply current [ma] vcc=6v rt=22k cs>2.35v oscillation frequency vs. operating mode supply current 0.0 0.5 1 .0 1 .5 2.0 2.5 3.0 1 0 1 00 1 000 oscillation frequency [khz] operating mode supply current [ma] vcc=6v duty=50% vcc vs. operating mode supply current 0.0 0.5 1 .0 1 .5 2.0 00.5 11 .5 2 2.5 3 vcc [v] operating mode supply current [ma] duty=50% in(-)-fb:shorted fosc= 1 mhz fosc= 1 85khz vcc vs. operating mode supply current 0.0 0.5 1 .0 1 .5 2.0 2.5 3.0 468 1 0 1 2 1 4 1 6 1 820 vcc [v] operating mode supply current [ma] duty=50% in(-)-fb:shorted fosc= 1 mhz fosc= 1 85khz
12 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e error amplifier gain and phase vs. frequency out terminal high side voltage vs. source current 0 50 1 00 1 50 200 250 300 350 400 450 05 1 0 1 52025 out terminal voltage [v] out terminal source current [ma] vcc=2.5v vcc= 6v vcc= 1 2v vcc=20v out terminal low side voltage vs. sink current 0 50 1 00 1 50 200 00.5 11 .5 out terminal voltage [v] out terminal sink current [ma]
13 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e 8 ? ? ? ? description of each circuit (1) reference voltage circuit this circuit consists of the reference voltage circuit using band gap reference, and also serves as the power supply of the internal circuit. the precision of output is 2.23v 3%. it is stabilized under the supply voltage of 2.5v or over. the precision of reference voltage of error amplifier circuit is 0.88v 2%, and the reference voltage circuit is connected to the non-inverting input of the error amplifier circuit. (2) oscillator the oscillator generates a triangular waveform by charging and discharging the built-in capacitor. a desired oscillation frequency can be determined by the value of the resistor ?r t ?connected to the rt terminal (fig. 1). the built-in capacitor voltage oscillates between approximately 0.66v and 1.1v with almost the same charging and discharging gradients. you can set the desired oscillation frequency by changing the gradients using the resistor connected to the rt terminal. (large r t : low frequency, small r t : high frequency) the oscillator waveform cannot be observed from the outside because a terminal for this purpose is not provided. the oscillator output is connected to the pwm comparator. (3) error amplifier circuit the in(-) terminal (pin3) is an inverting input terminal. the non- inverting input is internally connected to the reference voltage (0.88v 2%; 25 ). the fb terminal (pin4) is the output of the error amplifier. gain setting and phase compensation setting is done by connecting a capacitance and a resistor between the fb terminal and the in(-) terminal. vout which is the output voltage of dc to dc converter can be calculated by: 2 2 1 r r r v vout b + = gain a v between the vout and the fb terminal can be calculated by: 1 r r a nf v ? = (4) pwm comparator the pwm comparator has 4 input terminals. (fig. 4) the oscillator output is compared with the cs terminal voltage , and the error amplifier voltage ,then, the lower voltage between and is preferred. while the preferred voltage is lower than the oscillator output, the pwm comparator output is low. while the preferred voltage is higher than the oscillator output, the pwm comparator output is high(fig. 5). when the ic starts, the capacitor connected to the ?
fig.1 + ? ? ??e 9? ????e 6<; fig.3 ? ?6<;7<; ?:*033(;065?6<;7<; ?
?;,9405(3?=63;(., ?9969?4730-0,9?6<;7<; ??=63;(., fig.4 r t value : small r t value : large 0.66v 1.1v fig.2 oscillation output cs terminal volta g e dt voltage error amplifier output pwm output pulse fig.5
14 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e cs terminal is charged through the resistor connected to the power supply , and then the output pulses begin to widen gradually as the operation of soft start. in steady operation, the pulse width is determined based on the voltage of the error amplifier , and then the output voltage is stabilized. the dead time control voltage ( dt voltage) of fa7700 and fa7701 has different characteristics to adjust the ics to various types of power supply circuits being controlled and also to reduce external discrete components as many as possible. fa7700 is developed for fly-back circuits, and boost circuits, and the dt voltage is set in the ic so that the maximum output duty cycle is fixed to 80%(min.). (maximum output duty cycle changes according to operation frequencies.? see p10 ?maximum output duty vs. temperature?.) it prevents magnetic saturation of the transformer or the like when a short-circuit in the output circuit occurs. fa7701 is developed for buck circuits, and it is designed for the maximum output duty cycle of 100%. the timing chart of pwm comparator is described in fig. 5. (5) soft start function as described in fig. 6, r cs is connected between cs terminal and vcc terminal, and cs is connected between cs terminal and gnd. the voltage of cs terminal rises when starting the power supply, because cs is charged by vcc through rcs. the soft start function starts by charging a capacitor cs connected to pwm comparator. to estimate the soft start period, the time(ts) between the start and the moment when the width of output pulse reaches 50% is calculated by: y ) 88 . 0 ln( ] [ms ? vcc vcc rcs cs ts cs: capacity of cs [ f] rcs: resistance of rcs [k ] vcc: supply voltage [v] the maximum current flowing in rcs should be within the recommended value(50 a max.). l cc cs l cc i ua v m r i ua v + ? < < + ? 1 5 . 1 ] [ 50 5 . 1
(il: leak current of capacitor cs) note) this ic operates on/off function by the cs terminal(cs<0.3v typ. :off), then it turns off the internal bias voltage v ref (off mode). therefore, you can not connect the resistor ?rcs? between cs terminal and ref terminal, and can connect the resistor only to vcc terminal. yyyy (6) on/off circuit the on/off function can be controlled by external signal to the cs terminal,the ic becomes off mode .when the cs terminal voltage is below 0.30v(typ.), the output of on/off comparator c3 is set to low, and the internal power source v ref is shut off, then the ic is switched to the off mode. the power consumption in the off mode is 40 a(typ.). a sample circuit is given in fig. 7. + + <;7<; 6-- 1 .5v 2.2v 1 .5v 5.5v ?

: *: ?
? ?
?
?
+ 0.3 v ? ?
fig.6 fig.7

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15 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e (7) timer latch short-circuit protection circuit the short-circuit protection circuit consists of two comparators c1, c2(fig. 6). in steady operation, the output of s.c.det comparator c2 is set to high, and the cs terminal is clamped by the 1.5v zener diode,because the output of error amplifier is about 1v. if the converter output voltage drops due to a short-circuit etc, when the output voltage of error amplifier rises. excesses 1.5v, the output of s.c.det comparator c2 is set to low, and then the clamp of zener diode is turned off. as a result, the voltage of cs terminal rises up to the lower value of either 5.5 v or the voltage of vcc terminal. if the voltage of cs terminal excesses 2.2v, the output of s.c.p comparator c1 is set to high,and the circuit shuts down the output circuit of the ic. when it occurs, the current consumption of the ic is 0.9ma(typ.) because the ic is set to off latch mode. the period (tp) between the occurrence of a short-circuit in the converter output and the triggering of the short-circuit protection function can be calculated by the following expression: y ) 2 . 2 5 . 1 ln( [ms] ? ? vcc vcc rcs cs tp cs: capacitance of cs[ f] rcs: resistance of rcs[k ] vcc: supply voltage [v] note) when the ic is used in a product with low vcc voltage, the period (tp) of the triggering of the short- circuit protection described above fluctuates significantly. therefore, sufficient care should be taken in such cases. ex.) when rcs=750k , cs=0.1 f: vcc=2.5v: tp P 90ms vcc=3.6v: tp P 30ms you can reset the off latch mode operation of the short-circuit protection by either of the following ways: lowering the cs voltage below 2.03v(typ.); lowering the vcc voltage below the off threshold voltage of under voltage lock out ; 1.93v(typ.); lowering the voltage of fb terminal below 1.5v(typ.) the off latch mode action cannot be triggered by externally applying voltage of over 2.2 v forcibly to the cs terminal (1.5v,zd clamped) characteristics of the current and the voltage of cs terminal is shown in the characteristics curve [cs terminal voltage vs. cs terminal sink current] in page 10. be sure to use the ic up to the recommended cs terminal current of 50 a. fig.8 0 1 2 3 4 5 6 time 1.5v 2.2v lower value of either 5.5v or vcc terminal voltage start-up soft start momentary short circuit short circuit short circuit protection tp cs terminal voltage [v]
16 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e (8) output circuit the ic contains a push-pull output stage and can directly drive mosfets (fa7700: n ch, fa7701: p ch). the maximum peak current of the output stage is a sink current of +150ma, and a source current of - 400ma. the ic can also drive npn, and pnp transistors. the maximum peak current in such cases is 50ma. be sure to design the output current considering the rating of power dissipation. (9) power good signal circuit/ undervoltage lockout circuit the ic contains a protection circuit against undervoltage malfunctions to protect the circuit from the damage caused by malfunctions when the supply voltage drops. when the supply voltage rises from 0v, the circuit starts to operate at vcc of 2.07v(typ.) and outputs generate pulses. if a drop of the supply voltage occurs, it stops output at vcc of 1.93v(typ.). when it occurs, the cs terminal is turned to low level and then it is reset. the power good signal circuit monitors the voltage of ref terminal, and stops output until the voltage of ref terminal excesses approximately 2v to prevent malfunctions.
17 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e 9 ? ? ? ? design advice (1) setting the oscillation frequency as described in section 8(1), ?description of each circuit,? a desired oscillation frequency can be determined by the value of the resistor connected to the rt terminal. when designing an oscillation frequency, you can set any frequency between 50khz and 1mhz. you can roughly obtain the oscillation frequency from the characteristic curve ?oscillation frequency(fosc) vs. timing resistor resistance(r t )? or the value can be calculated by the following expression. 11 . 1 9 . 0 3000 3000 ? ? ? ? ? ? ? ? = = ? fosc r r fosc t t this expression, however, can be used for rough calculation, the value obtained is not guaranteed. the operation frequency varies due to the conditions such as tolerance of the characteristics of the ics, influence of noises, or external discrete components. when determining the values, be sure to verify the effectiveness of the values of the components in an actual circuit. (2) operation around the maximum or the minimum output duties as described in p9 of characteristic curves of ?fb terminal voltage (v fb ) vs.output duty cycle? and ?cs terminal voltage (vcs) vs. output duty cycle?, the linearity of the output duty of this ic drops around the minimum output duty and the maximum output duty(fa7701 only). this phenomena are conspicuous when operating in a high frequency(when the pulse width is narrow). therefore be careful when using high frequency. (3) restriction of external discrete components to achieve a stable operation of the ics, the value of external discrete components connected to vcc, ref, cs, fb terminals should be within the recommended operational conditions. (4) loss calculation since it is difficult to measure ic loss directly, the calculation to obtain the approximate loss of the ic connected directly to a mosfet is described below. when the supply voltage is vcc, the current consumption of the ic is icc, the total input gate charge of the driven mosfet is qg, the switching frequency is fsw, the total loss pd of the ic can be calculated by: pd P vcc (icc+qg fsw). the values in this expression is influenced by the effects of the dependency of supply voltage, the characteristics of temperature, or tolerance. therefore,be sure to verify appropriateness of the value considering the factors above under all applicable conditions. example) when vcc=6v, in the case of a typical ic, from the characteristic curve, icc=1.2ma. when operating in qg=6nc, fsw=500khz, pd should be: pd P 6 (1.2ma+6nc 500khz) P 25.2mw fosc: oscillation frequency [khz] r t : timing resistor [k ]
18 q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e q ualit y is our messa g e 10 ? ? ? ? application ?? tt ? ? ? ? t y

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