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an-057e rev.1.0 jun-2010 1 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 fuji power supply control ic dc/dc power supply control ic FA7703/7704 application note june-2010 fuji electric systems co.,ltd.
an-057e rev.1.0 jun-2010 2 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 1. this data book contains the pr oduct specifications , characteristics, data, ma terials, and structures as of june 2010. the contents are subject to change wit hout notice for specific ation 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 exemplif y 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 enhanc ing product quality and reliability, a small percentage of semiconductor products may become faulty. when using fuji electr ic 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 pr oducts 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 int ended for use in the followi ng electronic and electrical equipment, which has normal reliability requirements. ? computers ? oa equipment ? communi cations equipment (ter minal devices) ? measurement equipment ? machine tools ? audi ovisual equipment ? elec trical 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 malfunc tioning even if a fuji's product incorporated in the equipment becomes faulty. ? transportation equipment (mounted on cars and ship s) ? trunk communications equipment ? traffic-signal control equipment ? gas leakage detectors with an auto-shut-off feature ? emergency equipment for responding to disasters and ant i-burglary devices ? safety devices 6. do not use products in this da ta book for the equipment requiring strict reliability such as (without limitation) ? space equipment ? aeronautic equipm ent ? atomic control equipment ? submarine repeater equipment ? medical equipment 7. copyright ? 1995 by fuji electric co., ltd. all ri ghts reserved. no part of this data book may be reproduced in any form or by any means wit hout 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 s hall be liable for any injury caused by any use of the products not in accordance with instructions set forth herein. warning
an-057e rev.1.0 jun-2010 3 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 contents page 1. descrip tion ......................................................... 4 2. featur es ............................................................. 4 3. out line ................................................................ 4 4. block di agram .................................................... 5 5. selecti on guid e ................................................... 5 6. pin assi gnment .................................................. 5 7. ratings and char acterist ics ................................ 6 8. characterist ics curv es.......................................... 9 9. description of each circ uit .................................. 13 10. design advice .................................................... 16 11. applicati on circui t ............................................... 21 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.
an-057e rev.1.0 jun-2010 4 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 1. description FA7703/04 are the pwm type dc-dc converter control ics with 2ch output that c an directly drive power mosfets. FA7703/04 feature cmos devices with high breakdown voltage and also low power consumption are achieved. by m eans of their small and thin pack age (1.1mm max.), and high frequency operation (to 1mhz), FA7703/04 are completely suitabl e for the use of very small dc-dc converters. besides, you can select a pch or nch type of mosf et directly driven by FA7703/04, and also you can practically design any kind of dc-dc converter circuit like a boost converter, a buck converter, a inverting converter, a fly-back converter, and so on. 2. features z wide range of supply voltage FA7703 : vcc=2.5 to 30v fa7704 : vcc=2.5 to 20v z direct driving of mosfet z switching pch/nch driving is available (channel 1 only) z low current consumption is achieved by cmos process: 1.8ma (typ.) in operation z 2ch pwm control ic z high frequency operation is av ailable: 50khz to 1mhz z simple setting of operation frequency with a timing resistor z soft start setting is available z setting of the limitation of maximum out put duty cycle is available in each channel z built-in protection func tion for undervoltage lockout z highly accurate reference voltage: vref: 1.00v 1%, vb: 1.00v 2%, vreg: 2.20v 2% z built-in output timer latched s hort-circuit protection circuit z thin and small package: tssop-16, sop-16 3. outline tssop-16 (v) sop-16 (m) 0.71 0.1 5.3 0.3 0.4 0.05 1.27 7.8 0.2 1.9 0.2 10.2 0.3 4.40 0.05 0.65 6.4 0.1 5.0 0.1 1.10max units:mm
an-057e rev.1.0 jun-2010 5 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 4. block diagram 5. selection gide ch.1(out1) buck, boost, fly-back FA7703 ch.2(out2) buck, inverting (pch driven) ch.1(out1) buck, boost, fly-back fa7704 ch.2(out2) boost, fl y-back (nch driven) 6. pin assignment pin no pin symbol description 1 rt oscillator timing resistor 2 cs soft start, timer latched short circuit protection, on/off control 3 dt2 ch.2 dead time adjustment 4 in2+ ch.2 non-inverting input to error amplifier 5 in2- ch.2 inverting input to error amplifier 6 fb2 ch.2 output o error amplifier 7 gnd ground 8 out2 ch.2 output 9 vcc power supply 10 out1 ch.1 output 11 sel selection of type of driven mosfet (out1) 12 fb1 ch.1 output o error amplifier 13 in1- ch.1 inverting input to error amplifier 14 ref reference voltage 15 dt1 ch.1 dead time adjustment 16 reg regulated voltage output 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 reg dt1 ref in1- fb1 sel1 out1 vcc rt cs dt2 in2+ in2- fb2 gnd out2 + - + + + - + + osc power good signal reference voltage + - - uvlo bias 1v er.amp1 er.amp2 pwm.comp1 pwm.comp2 1.5v 2.0v 1.3v s.c.det s.c.p on/off on/off bias 2.2v i cs fa7704
an-057e rev.1.0 jun-2010 6 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 7. ratings and characteristics the contents are subject to change without notice. when using a product, be sure to obtain the latest specifications. (1)absolute maximum ratings item symbol ratings units FA7703 30 power supply voltage fa7704 v cc 20 v ref terminal output current i ref 1 ma reg terminal output current i reg 2 ma i sopeak -400(peak) ma out1, out2 terminal source current i socont -50(continuos) ma i sipeak +150(peak) ma out1, out2 terminal sink current i sicont +50(continuos) ma rt,cs,reg,ref,in1-,in2+,in2-,fb1, fb2,dt1,dt2,sel1 terminal voltage v logic +2.5(max.) -0.3(min.) v tssop 300 power dissipation (ta 25 c)* sop p d 400 mw operating ambient temperature t a -30 to +85 c operating junction temperature t j +125 c storage temperature t stg -40 to +150 c *:maximum dissipation curve at ta 25 c is shown under figure. (2)recommended operating conditions item symbol min. typ. max. units FA7703 2.5 6 28 supply voltage fa7704 v cc 2.5 6 18 v dc feedback re sistor of error amplifier r nf 100 k vcc terminal capacitance* c vcc 0.1 f reg terminal capacitance c reg 0.047 0.1 1 f cs terminal capacitance c cs 0.01 10 f oscillation frequency f osc 50 1000 khz pch,pnp driving v sel1l connect to gnd sel1 terminal voltage nch,npn driving v sel1h connect to reg terminal *please select the proper value by input-output conditions of power supply. maximum power dissipation curve 0 100 200 300 400 500 -30 0 30 60 90 120 150 ambient temperature ta[c] maximum power dissipation pd[mw] tsso sop
an-057e rev.1.0 jun-2010 7 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 (3)electrical characteristics [unless otherwise standard,ta=25 c,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 load current i ref =0ma 0.990 1.000 1.010 v line regulation v linef FA7703:vcc=2.5 to 28v,i ref =0ma fa7704:vcc=2.5 to 18v,i ref =0ma 1 5 mv load regulation v ldf iref=0 to 1ma -10 -3 mv variation with temperature v tcf ta=-30 to +85 c change rate for value at 25 c -0.8 to +0.2 % (2) regulated voltage for in ternal control blo cks section (reg te rminal voltage) item symbol conditions min. typ. max. units output voltage v reg reg terminal load current i reg =0ma 2.156 2.200 2.244 v line regulation v lineg FA7703:vcc=2.5 to 28v,i reg =0ma fa7704:vcc=2.5 to 18v,i reg =0ma 4 14 mv load regulation v ldg i reg =0 to 2ma -12 -2 mv variation with temperature v tcg ta=-30 to +85 c change rate for value at 25 c -0.8 to +0.2 % (3) oscillator section item symbol conditions min. typ. max. units oscillation frequency f osc r t =22k 160 190 220 khz line regulation f line FA7703:vcc=2.5 to 28v fa7704:vcc=2.5 to 18v 0.1 % f tc1 ta=+25 to -30 c , f=50k to 1mhz 2 % variation with temperature f tc2 ta=+25 to +85 c , f=50k to1mhz 3 % (4) error amplifier section (input:in1-,in2+,in2-,output:fb1,fb2 terminal) item symbol conditions min. typ. max. units reference voltage (ch1) v b in1- terminal threshold voltage 0.980 1.000 1.020 v input offset (ch2) v ofst (in2+) - (in2-) - - 10 mv common mode input voltage v in 0.3 1.4 v input current i in -100 0 +100 na open loop gain a vo 70 db unity gain bandwidth f t 1.5 mhz output source current i ohe fb1,2 terminal voltage=v ref -0.5v -220 -160 -100 a output sink current i ole fb1,2 terminal voltage=0.5v 3 6 12 ma (5) pulse width modulation se ction (fb1,fb2 terminal) item symbol conditions min. typ. max. units input threshold voltage v fb0 duty cycle=0% 0.550 0.650 0.750 v input threshold voltage v fb100 duty cycle=100% 1.000 1.100 1.200 v (6) dead time adjustment circuit section (dt1, dt2 terminal) item symbol conditions min. typ. max. units input threshold voltage v dt0 duty cycle=0% 0.550 0.650 0.750 v input threshold voltage v dt100 duty cycle=100% 1.000 1.100 1.200 v
an-057e rev.1.0 jun-2010 8 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 (7) under voltage lock-out section (vcc terminal) item symbol conditions min. typ. max. units on threshold v ccon 2.00 2.25 v off threshold v ccof 1.40 1.85 v hysteresis voltage v cchy 0.05 0.15 0.35 v ta=-30 to +25 c +0.3 mv/c variation with temperature v cchy ta=+25to +85 c -0.1 mv/ c (8) soft start section (cs terminal) item symbol conditions min. typ. max. units output source current i cs cs=0v -2.8 -2.2 -1.6 a threshold voltage1 v cs0 duty cycle=0% 0.550 0.650 0.750 v threshold voltage2 v cs50 duty cycle=50% 0.880 v (9) 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 v latched mode threshold voltage v csth cs terminal voltage 1.900 2.000 2.100 v latched mode reset voltage v csre cs terminal voltage 1.830 v latched mode hysteresis v cshy cs terminal voltage 30 170 300 mv v cscl1 fb terminal voltage<1.35v 1.200 1.270 1.340 v cs terminal clamped voltage v cscl2 fb terminal voltage>1.65v 2.120 2.200 2.280 v (10) output stage section (out1,out2 terminal,sel1 terminal) item symbol conditions min. typ. max. units high side on resistance r onh v cc =6v,source current=-50ma 10 20 high side on resistance r onh v cc =2.5v,source current=-50ma 18 36 low side on resistance r onl v cc =6v,sink current=+50ma 5 10 low side on resistance r onl v cc =2.5v,sink current=+50ma 5 10 trn 330pf load to gnd terminal 20 ns rise time trp 330pf load to vcc terminal 20 ns tfn 330pf load to gnd terminal 35 ns fall time tfp 330pf load to vcc terminal 35 ns v sel1l pch-mosfet, pnp transistor driving 0 0.2 v sel1 terminal input voltage v sel1h nch-mosfet, npn transistor driving v reg - 0.2 v reg v (11) overall section (vcc terminal) item symbol conditions min. typ. max. units i cc0 duty cycle=0%,out1/2:open cs=0v, fb1,fb2 v reg r t =22k ,f 190khz 1.3 1.9 ma i cc1 duty cycle=80%,out1/2:open r t =22k ,f 190khz 1.8 2.7 ma operating mode supply current i cc2 duty cycle=80%,out1/2:open r t =3k ,f 1mhz 3.1 4.7 ma latched mode supply current i cclat cs>2.1v,fb1,fb2 v reg , r t =22k ,f 190khz 1.3 1.9 ma
an-057e rev.1.0 jun-2010 9 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 8. characteristics curves timing resistor vs.oscillation fr equency 10 100 1000 110100 timing resistor rt[k ] oscillation frequency [khz] vcc=6v oscillation fr equency vs.ambient temperature 185 186 187 188 189 190 191 192 193 194 195 -40 -20 0 20 40 60 80 100 ambient temperature ta[c] oscillation frequency [khz] vcc=6v,rt=22k regulated voltage vs.supply voltage vcc 2.18 2.19 2.20 2.21 2.22 0 5 10 15 20 supply voltage vcc[v] regulated voltage vreg[v] ireg=0a,rt=22k regulated voltage vs.ambient temperature 2.16 2.17 2.18 2.19 2.20 2.21 2.22 2.23 2.24 -40-20 0 20406080100 ambient temperature ta[c] regulated voltage vreg[v] ireg=0a,rt=22k reference voltage vs.supply voltage vcc 0.990 0.995 1.000 1.005 1.010 0 5 10 15 20 supply voltage vcc[v] reference voltage vref[v] iref=0a,rt=22k reference voltage vs.ambient temperature 0.98 0.99 1.00 1.01 1.02 -40-20 0 20406080100 ambient temperature ta[c] reference voltage vref[v] iref=0a,rt=22k
an-057e rev.1.0 jun-2010 10 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 fb terminal voltage vs.duty cycle 0 10 20 30 40 50 60 70 80 90 100 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 fb terminal voltage [v] duty cycle [%] FA7703/04:out1 nch driven (sel1=reg) fa7704:out2 fosc=1mhz fosc=190khz fb terminal voltage vs.duty cycle 0 10 20 30 40 50 60 70 80 90 100 0.50.60.70.80.91.01.11.2 fb terminal voltage [v] duty cycle [%] fosc=1mhz fosc=190khz FA7703/04:out1 pch driven (sel1=gnd) FA7703:out2 dt terminal voltage vs.duty cycle 0 10 20 30 40 50 60 70 80 90 100 0.50.60.70.80.91.01.11.2 dt terminal voltage [v] duty cycle [%] fosc=1mhz fosc=190khz FA7703/04:out1 nch driven (sel1=reg) fa7704:out2 dt terminal voltage vs.duty cycle 0 10 20 30 40 50 60 70 80 90 100 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 dt terminal voltage [v] duty cycle [%] fosc=1mhz fosc=190khz FA7703/04:out1 pch driven (sel1=gnd) FA7703:out2 cs terminal voltage vs.duty cycle 0 10 20 30 40 50 60 70 80 90 100 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 cs terminal voltage [v] duty cycle [%] fosc=1mhz fosc=190khz FA7703/04:out1 nch driven (sel1=reg) fa7704:out2 cs terminal voltage vs.duty cycle 0 10 20 30 40 50 60 70 80 90 100 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 cs terminal voltage [v] duty cycle [%] fosc=1mhz fosc=190khz FA7703/04:out1 pch drivenb (sel1=gnd) FA7703:out2
an-057e rev.1.0 jun-2010 11 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 duty cycle vs. ambient temperature 78 80 82 84 86 88 90 92 94 -40-20 0 20406080100 ambient temperature ta[c] duty cycle [%] dt terminal voltage 1.05v fosc=190khz fosc=1mhz FA7703/04:out1 nch drive (sel1=reg) fa7704:out2 duty cycle vs. ambient temperature 78 80 82 84 86 88 90 92 94 -40 -20 0 20 40 60 80 100 ambient temperature ta[c] duty cycle [%] dt terminal voltage 1.05v fosc=190khz fosc=1mhz FA7703/04:out1 pch drive (sel1=gnd) FA7703:out2 operating mode supply current vs.supply voltage 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 supply voltage vcc[v] operating mode supply current [ma] duty=80%, in(-)-fb:shorted fosc=190khz fosc=1mhz cs terminal voltage vs.ambient temperature 1.21 1.23 1.25 1.27 1.29 1.31 1.33 -40 -20 0 20 40 60 80 100 ambient temperature ta[c] cs terminal voltage [v] fb1,fb2<1.35v operating supply current vs.ambient temperature 1.0 1.5 2.0 2.5 -40-20 0 20406080100 ambient temperature ta[c] operating supply current [ma] duty=80% rt=22k vcc=6v
an-057e rev.1.0 jun-2010 12 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 out terminal high side voltage vs. source current 0 50 100 150 200 250 300 350 400 450 0 5 10 15 20 25 out terminal voltage [v] out terminal source urrent [ma] out1/2 vcc=20v vcc=2.5v vcc=4.5v vcc=6.0v out terminal low side voltage vs.sink current 0 20 40 60 80 100 120 140 160 180 200 0.0 0.5 1.0 1.5 2.0 2.5 out terminal voltage [v] out terminal sink current [ma] out1/2 error amplifier gain and phase vs.frequency -20 -10 0 10 20 30 40 50 60 70 80 frequency [hz] gain [db] -20 0 20 40 60 80 100 120 140 160 180 phase [deg] gain phase 1 1k 10k 100k 1m 10m 10 cs terminal source current vs.ambient temperature -2.40 -2.35 -2.30 -2.25 -2.20 -2.15 -2.10 -2.05 -2.00 -40-20 0 20406080100 ambient temperature ta[c] cs terminal source current [ a]
an-057e rev.1.0 jun-2010 13 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 9. description of each circuit (1)reference voltage circuit the reference voltage circuit of FA7703/04 generates the reference voltage (vref) of 1.00v1% compensated in temperature from vcc voltage, and the regulated voltage (vreg) of 2.2v 2% for internal controlling. these voltages start to output when the undervoltage lockout protection (uvlo) is cancelled, and they stabilize after the supply voltage (vcc) reaches up to approx. 2.4v or higher. the reference voltage (vref) is connected to the non-inverting input of error amplifier 1 and serves as the reference voltage of error amplifier 1. because of error amplifiers have offset voltage then, the precision of voltage in practical use is 1.00v2%. the voltage (vref) outputs externally from ref terminal, therefore, it can serve as a stabilized power source. when using it, be sure to set the output current 1ma or below. the regulated voltage (vreg) for internal controlling serves as the stabilized power source for maximum output duty setting or the like. be sure to set the output current 2ma or below in operation in this case. this voltage also serves as the control power source of all the internal circuits of FA7703/04. a capacitor for stabilization (creg) is needed to be connected to the vr eg terminal. see recommended operating conditions to determine capacitance. (2)oscillator the oscillator of FA7703/04 generates triangular waveforms by charging and discharging the built-in capacitor. any desired oscillation frequency can be obtained by setting the value of the resistor connected to rt terminal (fig. 1). the voltage oscillates between approximately 0.65v and 1.10v in charging and discharging with almost the same gradients (fig. 2). your desired oscillation frequency can be determined by changing the gradient using the resistor (rt) connected to rt terminal. (large rt: low frequency, small rt: high frequency) the waveforms of oscillator cannot be observed from the outside because a terminal for this purpose is not provided. approximately dc 1v is output to rt terminal. the oscillator output is connected to pwm comparator. (3)error amplifier circuit error amplifier 1 of FA7703/04 has the inverting input in1(-) terminal (pin13). the non-inverting input is internally connected to the reference voltage (vb) of 1.00v2% at 25c. because error amplifier 2 of FA7703/04 has the inverting input in2(-) terminal (pin5) and non-inverted input in2(+) terminal (pin4) outputting externally, various circuit can be designed by kinds of external circuit structur es. fb terminals (pin6, pin12) are the outputs of error amplifiers. voltage gain and phase compensation can be set by connecting a capacitor (c) and a resistor (r) between fb terminal and in(-) terminal.(fig. 3) for more information about the connection for each output voltage of power supply, refer to design advice. fig.2 r t value: large r t value: small 0.65v 1.10v fig.3 1 osc rt r t fig.1 12 13 4 5 6 14 comp comp v b (1.0v) er.amp.1 er.amp.2 in1- ref fb1 fb2 in2- in2+ vout1 vout2 c fb 1 r1 r2 r3 r4 r fb 1 c fb 2 r fb 2
an-057e rev.1.0 jun-2010 14 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 (4)pwm comparator pwm comparator of FA7703/04 has 4 input terminals. (fig. 4) the oscillator output 2 is compared with the cs terminal voltage 1 , the dt terminal voltage 3 , and the error amplifier output 4 . among those 3 inputs of 1 , 3 , and 4 , the one with the lowest voltage is chosen and given priority. while the value of the chosen voltage is lower than the value of the waveform of oscillator output, pwm comparator output is set to low. similarly, while the value of the chosen voltage is higher than the waveform of oscillator output, pwm comparator output is set to high. (fig. 5) when FA7703/04 are turning on, the soft start function starts according to the cs terminal voltage 1 , then the output pulses begin to widen gradually. the maximum pulse width is adjusted by changing the dt terminal voltage. in steady operation, the pulse width is determined with the condition of the error amplifier output 4 , and then the output voltage of dc-dc converter is stabilized. the operation flow chart of pwm comparator and out terminal is shown in fig. 5. the output polarity of out1 terminal changes according to the condition of sel1 terminal. the polarity of out 2 terminal is different between FA7703 and fa7704; accordingly, select the type for your desired circuit design. (5)soft start function as described in fig. 6, a capacitor c cs is connected to cs terminal. when the power supply of FA7703/04 starts and the undervoltage lockout protection circuit (uvlo) is cancelled, the capacitor c cs is charged by the internal current source (2.2 a. typ.), and the voltage of cs terminal rises gradually. since the voltage of cs terminal is connected to pwm comparator, the output pulses begin to widen gradually, and then the soft start function starts as a result. (fig. 5) (6)timer latch short-circuit protection circuit the short-circuit protection circuit of FA7703/04 consists of two comparators. (s.c. det comparator, s.c.p comparator) in steady operation, the output of error amplifier is approximately 1v, accordingly, the output of s.c.det comparator is set to high, and the voltage of cs terminal is clamped at 1.27v. if the output voltage drops due to a short-circuit or the like, the output voltage of error amplifiers rises. when the output voltage of error amplifiers exceeds 1.5v(typ.), the output of s.c.det comparator is set to low, and the clamp action at the cs terminal voltage of 1.27v is cancelled, then the voltage of cs terminal rises up to the vreg voltage. when the voltage of cs terminal exceeds 2.0v(typ.), the output of s.c.p comparator is set to high, accordingly, the output of FA7703/04 is shut off. in this case, FA7703/04 operate in off latch mode and the current consumption in this mode is 1.3ma(typ.). the operating waveform of the voltage of cs terminal is shown in fig. 7. the approximate time (tp) between the + - + + oscillation voltage cs terminal voltage dt terminal voltage error amplifier output pwm output 1 2 3 4 fig.4 + - - 1.5v 2.0v 1.27v s.c.det s.c.p fb uvlo output off 2 2.2 a c cs cs vcc fig.6 fig.5 pwm output out1 nch driven (sel1:reg) out1 pch driven (sel1:gnd) out2 FA7703 out2 fa7704 oscillation voltage cs terminal voltage dt terminal voltage error amplifier output 4 3 1 2
an-057e rev.1.0 jun-2010 15 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 occurrence of a short-ci rcuit in the output and the triggering of the short-circuit protection function can be calculated with cs cs i c 0.7 tp[s] where, c cs : capacitance of cs terminal [ f] i cs : output source current of cs terminal [ a] (2. 2? , typ.) you can reset the timer latch action for the short-circuit protection function by changing the voltage of either vcc terminal or cs terminal to the following values. vcc terminal: below uvlo voltage (1.85v typ.) cs terminal: below 1.83v(typ.) (7)output circuit FA7703/04 contain a push-pull output stage and can directly drive mosfets. the peak current of out terminal is the maximum sink current of +150ma, and the source current of -400ma. FA7703/04 can also drive both npn and pnp type transistors. and in such cases, the maximum continuous current is 50ma. when designing the value of output current, be sure to consider the allowable loss accordingly. (see design advice) ch1 of FA7703/04 is available for driving both types of mosfets and you can determine the type of mosfet, which is connected externally by selecting the connection of sel1 terminal (pin11). if sel terminal is connected to gnd terminal, FA7703/04 can drive a pch mosfet. if sel terminal is connected to reg terminal, they can drive nch mosfet. you can accordingly design a buck converter circuit by pch mosfet driving, and a boost circuit or a fly-back converter circuit by nch mosfet driving. do not leave sel1 terminal open in operation, and be sure to connect it to either gnd terminal or reg terminal. (8)power good signal/undervoltage lockout protection circuit (uvlo) to protect FA7703/04 from malfunction when the supply voltage drops, there is built-in undervoltage lockout as a protection circuit. when the supply voltage rises from 0v, the uvlo circuit is canceled at vcc of 2.0v(typ.). when the supply voltage drops, the uvlo circuit shuts off the output at vcc of 1.85v(typ.). in this case, cs terminal is reset to low level. power good signal circuit monitors the voltage of reg terminal, and it stops the output of FA7703/04 until the voltage of reg terminal exceeds approximately 1.9v in order to protect the ics from malfunction. fig.7 0.5 1.5 1.0 2.0 start-up soft start momentary short circuit short circuit short circuit protection tp time cs terminal voltage [v] 1.27v 2.2v 0
an-057e rev.1.0 jun-2010 16 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 10. design advice (1)setting oscillation frequency as described in ?(2) oscillator? of ?description of each circuit?, any desired oscillation frequency can be obtained by setting the value of the resistor connected to rt terminal. (fig. 1) the desired oscillation frequency should be set between 50khz and 1mhz . the oscillation frequency to rt can be obtained from the chart of ?oscillation frequency vs. timing resistor? characteristic curves or by calculating with the formulas below. 1 . 1 3 -0.907 3 10 3 10 3 ? ? ? ? ? ? ? ? = = fosc r r fosc t t where, fosc: oscillation frequency [khz] r t : timing resistor [k ] these formulas can only be used for rough calculation; accordingly, be careful when designing, because the value obtained is not guaranteed. the operation frequency varies due to the conditions of the tolerance of ic influence for noises, or external discrete components etc. when determining the values, be sure to verify the effectiveness of the va lues you calculated in an actual circuit operation. because it is easily affected by noises by the high impedance, the resistor r t should be connected as shortly as possible near rt terminal and gnd terminal, (2)operation around the maximum or the minimum output duty cycle as described in the charts of ?fb terminal voltage vs. output duty cycle?, ?dt terminal voltage vs. output duty cycle?, ?cs terminal voltage vs. output duty cycle? characteristic curves, the output duty of FA7703/04 changes sharply around the minimum and the maximum output duty. this phenomenon occurs more conspicuously when operating in a high frequency (i.e. when the pulse width is narrow). cautious care must be taken when using high frequency. (3)determining soft start period the time from the start of charging cs terminal to n% output duty cycle can be roughly calculated by the following expression. cs cs csn i c v s ts = ] [ where, v csn : cs terminal voltage in the output duty of n% [v] c cs : capacitance of capacitor of cs terminal [ f] i cs : output source current of cs terminal [ a] 2.2 ? (typ.) v csn represents the voltage of cs terminal in the output duty of n%, a nd it changes according to the operation frequency. the value is obtained simply from the chart of ?cs terminal voltage vs. output duty cycle? characteristic curves. since the output source current of cs terminal is 2.2 ? , which it is rather sm all, if the capacitor has leak current, then the period of soft start (ts) is easily affected. therefore, cautious care must be taken when determining the value. charging of cs terminal begins after uvlo is cancelled. note that the time from power-on of power supply to start of charging ccs is t0 which is not zero as described in fig. 8. be careful. to reset the soft start function, the voltage of cs terminal is discharged with FA7703/04?s internal switch triggered by lowering the voltage of power supply below the voltage of uvlo (1.85v, typ.). if power supply restarts before the voltage is sufficiently discharged, the soft start function might not properly operate. accordingly, cautious care must be taken about it. vcc cs terminal voltage v csn threshold voltage t 0 ts fig.8 t0 : time from power-on of vcc to reaching unlock voltage of uvlo
an-057e rev.1.0 jun-2010 17 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 (4)setting the maximum output duty if you need to control the maximum output duty in the dc-dc converter circuit, you can control pulse width by connecting reg terminal to dt terminal divided with resistors r5 and r6, as described in fig. 9. the output duty of the voltage of dt terminal in this case changes according to the operation frequency, as described in the chart of ?dt terminal voltage vs. output duty cycle? characte ristic curves. set the output duty accordingly based on your required operation frequency. if the maximum output duty setting is not needed, be sure to connect dt terminal directly to reg terminal. in this case, the pulse width widens up to the output duty of 100%. the voltage of dt terminal should be set in the range of 0.65v to 1.1v(typ.). there is a possibility of distortion of the output pulses if strong noises or the like are applied to dt terminal. when conducting pattern wiring, do it as close to each terminal of the ic as possible. besides, it is strongly recommended to connect a capacitor c dt for a filter of noise prevention. (5)pull-up/pull-down resistor at the output section the power source of FA7703/04 to control the output section is supplied from the voltage of vreg, the voltage of this power source is accordingly not stationary below the uvlo voltage. on the other hand, out terminal becomes unsteady condition while power supply voltage is below uvlo voltage. be sure to connect a pull-up resistor/pull-down resistor according to fig. 10. (see fig. 10) (6)restriction of external discrete components/recommended operating conditions to achieve a stable oper ation of FA7703/04, the values of external discrete components connected to vcc, ref, and cs terminals of this ic should be within the range of recommended operating conditions. and also the voltage and the current applied to each terminal should be within the recommended operating conditions. a pch mosfet is installed between vcc terminal and out1 terminal, and between vcc terminal and out2 terminal. since the pch mosfet has a parasitic diode, if the voltage of out1 and out2 terminals becomes higher than the vcc terminal voltage, the current flows from each terminal to vcc terminal. cautious care must be taken accordingly when designing. 10 9 7 vcc gnd out1 v in 8 9 7 vcc gnd out2 v in fig.10 fig.9 3 15 16 7 reg dt1 or dt2 gnd r5 r6 c dt 3 15 16 7 reg dt1 or dt2 gnd setting maximum duty cycle not needed maximum duty cycle
an-057e rev.1.0 jun-2010 18 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 (7)loss calculation since it is difficult to measure ic loss directly, the calculation to obtai n 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 i cc1 , the total input gate charge of the driven mosfet is qg and the switching frequency is fsw, the total loss pd of the ic can be calculated by: pd vcc (i cc1 +qg fsw). the value in this expression is influenced by the effects of the dependency of supply voltage, the characteristics of temperature, or the tolerance of parameter. therefore, evaluate the appropriateness of ic loss sufficiently considering the range of values of above parameters under all conditions. example) i cc1 =1.8ma for vcc=6.0v in the case of a typical ic from the characteristics curve. qg=6nc, fsw=190khz, the ic loss ?pd? is as follows. pd 6.0 (1.6ma+6nc 190khz) 17.6mw if two mosfets are driven under the same condition for 2 channels, pd is as follows: pd 6.0 {1.8ma+2 (6nc 190khz)}=24.5mw (8)performance of output stage the performance of the output stage of FA7703/04 is the maximum sink current of 150ma and the maximum source current of 400ma. the switching element externally attached to FA7703/04 might affect switching speed of the ics. cautious care must be taken about it especially in high frequency operation. if the performance of the ics is not sufficient for your design, consider adding a buffer circuit to improve the performance. (9)in the case of bipolar driving if using a bipolar transistor as the switching element, there is a possibility of the damage from burnout due to excessive current flow because the ics doesn?t contain an internal limiter resistance. therefore, be sure to install a base resistor. (fig. 11) in the case of driving a bipolar transistor, control the output current of out terminal within 50ma(continuous) in operation. if you want to speed up the switching speed, it is quite effective to install a capacitor c b in addition. (10)on/off control FA7703/04 can be turned on/off at cs terminal by external signal. the way to conduct on/off control is also shown in fig. 12. when the voltage of cs terminal is below the threshold voltage, the duty becomes 0% and the output turns off. the current consumption in this case is 1.3ma(typ.). to switch the ics on, just turning cs terminal open, then the soft start function restarts, and the output turns back on. on/off control at cs terminal is used for both channel, and the control of each channel is not allowed. 10 8 9 7 vcc gnd out1 2 power supply r b c b fig.11 + - + + pwm.comp oscillation output cs terminal voltage dt terminal voltage error amplifier output output 12 7 2 + - + + dt terminal voltage 6 error amplifier output output on/off fig.12
an-057e rev.1.0 jun-2010 19 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 (11)setting of the output voltage of dc-dc converter figure 13 shows the ways to set each channel of the output voltage of dc-dc converter. the precision of output voltage based on FA7703/04?s characteristics depends on the variation of the voltage of vb (2%) and vref (1%), and also on offset voltage, and temperature characteristics. selection guide ch1 buck, boost, fly-back FA7703 ch2 buck, inverting (pch driven) ch1 buck, boost, fly-back fa7704 ch2 boost, fly-back (nch driven) if using FA7703/04, and building: in the case of a boost, a buck, or a fly-back circuit in ch1, the output voltage can be calculated with: b v r r r vout + = 2 2 1 1 if using FA7703, and building: a buck circuit in ch2, the output voltage can be calculated with: ref v r r r vout + = 3 4 3 2 a inverting circuit in ch2, the output voltage can be calculated with the following formula. (the output voltage is negative.) ref v r r v r r r vout ? + = 3 4 1 3 4 3 2 ,where ref r r r v v 8 7 8 1 + = the ratio of resistance can be calculated with: 1 2 1 4 3 v vout v v r r ref + ? = (use the absolute value of vout2 voltage) if setting r7=r8, then, ? ? ? ? ? ? ? = 3 2 4 3 2 r r r v vout ref if using fa7704, and building: a boost, or fly-back circuit in ch2, the output voltage can be calculated with: ref v r r r vout + = 3 4 3 2 13 12 11 7 10 + - vout1 vout1 r1 r2 v b (1.0v) in1- fb1 out1 sel1 ch1:buck(FA7703/04) 13 12 11 7 16 10 + - vout1 vout1 r1 r2 v b (1.0v) in1- fb1 out1 sel1 reg ch1:boost(FA7703/04) 4 14 8 6 5 7 + - vout2 vout2 r3 r4 in2- fb2 out2 in2+ ref ch2:buck(FA7703) 4 14 8 6 5 7 + - vout2 vout2 r3 r4 in2- fb2 out2 in2+ ref r7 r8 ch2:inverting(FA7703) v1 4 14 8 6 5 7 + - vout2 vout2 r3 r4 in2- fb2 out2 in2+ ref ch2:boost(fa7704) please note that do not leave sel1 terminal open in operation, and be sure to connect it to gnd or vreg terminal. fig.13
an-057e rev.1.0 jun-2010 20 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 (12)to protect FA7703/04 from application of negative voltage if rather large negative voltage is applied to any terminal of FA7703/04, then internal parasitic elements start operating, and they may cause malfunctions. accordingly, the negative voltage, which is applied to each terminal of the ics, must be kept above -0.3v. in the case of out terminal, in particular, the oscillation of voltage occurring after mosfet?s turning off can be applied to out terminal through mosfet?s parasitic capacitance. as a result, there is a possibility that the negative voltage is applied to out terminal. if this negative voltage reaches -0.3v or below, connect an schottky barrier diode between out terminal and gnd terminal as shown in fig. 14. the schottky barrier diode?s forward direction voltage clamps the voltage applied to out terminal. in this case, use the schottky barrier diode with low voltage drop in forward direction. other terminals should be kept above -0.3 v also based on the same reasons. (13)forbidden use of external forcible latched operation for cs terminal if the external voltage of 2.0v or more is forcibly applied to cs terminal in normal operation (clamped at 1.2v), the ic may be seriously damaged because the clamp circuit is not equipped with any resistor for limiter. therefore, do not apply external high voltage to cs terminal. 10 8 9 7 vcc gnd out1 2 sbd fig.14
an-057e rev.1.0 jun-2010 21 FA7703/04 http://www.fujielectric.co.jp/fdt/scd/ fuji electric systems co., ltd. FA7703/7704 11. application circuit FA7703 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 rt cs dt2 in2+ in2- fb2 gnd out2 reg dt1 ref in1- fb1 sel1 out1 vcc vin 2.5 to 8.0v 10v/100ma -7.5v/100ma 9k 1k 1k 11k 10k 2200pf 0.1 f 11k 10k 10k 1 f 1k 16k 10k 10k 22k 4700pf vin 8 to 18v 5v/500ma 30v/20ma fa7704 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 rt cs dt2 in2+ in2- fb2 gnd out2 reg dt1 ref in1- fb1 sel1 out1 vcc 4k 1k 10k 4700pf 0.1 f 10k 11k 10k 1.5k 0.1 f 43k 10k 4700pf

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