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vfm step-up dc/dc converter rh5ri 1b/ 2b/ 3b series application manual no.ea-025-0006
vfm step-up dc/dc converter 1 rh5ri 1b/ 2b/ 3b series outline the rh5ri 1b/ 2b/ 3b series are vfm (chopper) step-up dc/dc converter ics with ultra low supply current by cmos process. the rh5ri 1b ic consists of an oscillator, a vfm control circuit, a driver transistor (lx switch), a reference voltage unit, an error amplifier, resistors for voltage detection, and an lx switch protection circuit. a low ripple, high efficiency step-up dc/dc converter can be constructed of this rh5ri 1b ic with only three external com- ponents, that is, an inductor, a diode and a capacitor. the rh5ri 2b ic uses the same chip as that employed in the rh5ri 1b ic and is provided with a drive pin (ext) for an external transistor instead of an lx pin, so that a power transistor with a low saturation voltage can be externally provided, whereby a large current can be caused to flow through the inductor and accordingly a large current can be obtained. therefore, the rh5ri 2b ic is recommendable to the user who need a current as large as several tens ma toseveral hundreds ma. the rh5ri 3b ic also includes an internal chip enable circuit so that it is possible to set the standby sup- ply current at max. 0.5a. these rh5ri 1b/ 2b/ 3b ics are suitable for use with battery-powered instruments with low noise and ultra low supply current. ? small number of external components .......... only an inductor, a diode and a capacitor (rh5ri 1b) ? ultra low input current ................................... typ. 4a (rh5ri301b/303b at no load,with 1.5v input) ? high output voltage accuracy ......................... 2.5% ? low ripple and low noise ? low start-up voltage (when the output current is 1ma) ...................... max. 0.9v ? high efficiency ................................................... typ.80% ? low temperature-drift coefficient of output voltage .......................... typ. 50 ppm/?c ? small packages ................................................... sot-89 (rh5ri 1b, rh5ri 2b) sot-89-5 (rh5ri 3b) features applications ? power source for battery-powered equipment. ? power source for cameras, camcorders, vcrs, pdas, electronic data banks,and hand-held communication equipment. ? power source for appliances which require higher cell voltage than that of batteries used in the appliances.
2 rh5ri C ? part number -- - ab c selection guide in rh5ri series, the output voltage, the driver, and the taping type for the ics can be selected at the user's request. the selection can be made by designating the part number as shown below : for example, the product with output voltage 5.0v, the external driver (the oscillator frequency 100khz) and taping type t1, is designated by part number rh5ri502b-t1. code contents setting output voltage (v out ): a stepwise setting with a step of 0.1v in the range of 2.5v to 7.5v is possible. designation of driver: 1b: internal lx tr. driver (oscillator frequency 100khz) b 2b: external tr. driver (oscillator frequency 100khz) 3b: internal tr./external tr. (selectively available) (oscillator frequency 100khz, with chip enable function) designation of taping type : c ex. sot-89 : t1, t2 sot-89-5 : t1, t2 (refer to taping specification) t1 is prescribed as a standard. rh5ri block diagram lx vss ext lxsw ce error amp. out v lx limiter buffer vfm control osc 100khz chip enable vref + (note) lx pin ............ only for rh5ri 1b and rh5ri 3b ext pin ......... only for rh5ri 2b and rh5ri 3b ce pin ........... only for rh5ri 3b } } }
3 ? sot-89-5 pin configuration ? sot-89 pin description pin no. 1b 2b 3b 11 5 22 2 3 4 3 3 1 12 3 (mark side) 12 3 (mark side) 5 4 rh5ri symbol description v ss ground pin out step-up output pin, power supply (for device itself) lx switching pin (nch open drain) ext external tr. drive pin (cmos output) ce chip enable pin (active low) 1a/ 2b
absolute maximum ratings are threshold limit values that must not be exceeded even for an instant under any conditions. moreover, such values for any two items must not be reached simultaneously. operation above these absolute maximum ratings may cause degradation or permanent damage to the device. these are stress ratings only and do not necessarily imply functional operation below these limits. 4 rh5ri absolute maximum ratings symbol item v out output pin voltage v lx lx pin voltage v ext ext pin voltage v ce ce pin voltage i lx lx pin output current i ext ext pin current p d power dissipation topt operating temperature range tstg storage temperature range tsolder lead temperature (soldering) rating unit note +12 v +12 v note1 C0.3 to v out + 0.3 v note2 C0.3 to v out + 0.3 v note3 250 ma note1 50 ma note2 500 mw C30 to + 80 ?c C55 to + 125 ?c 260?c,10s ( note 1) applicable to rh5ri 1a and rh5ri 3b. (note 2) applicable to rh5ri 2b and rh5ri 3b. (note 3) applicable to rh5ri 3b. vss=0v absolute maximum ratings
5 electrical characteristics ? rh5ri301b symbol item v out output voltage v in input voltage vstart start-up voltage vhold hold-on voltage i in 1 input current 1 i in 2 input current 2 i lx lx switching current i lx leak lx leakage current fosc maximum oscillator frequency maxdty oscillator duty cycle h efficiency v lx lim v lx voltage limit conditions min. typ. max. unit note 2.925 3.000 3.075 v 8v i out =1ma,v in :0 ? 2v 0.8 0.9 v i out =1ma,v in :2 ? 0v 0.7 v to be measured at v in at no load 48a to be measured at v in 25a v in =3.5v v lx =0.4v 60 ma v lx =6v,v in =3.5v 0.5 a 80 100 120 khz on (v lx l ) side 65 75 85 % 70 80 % lx switch on 0.65 0.8 1.0 v note v out =3.0v rh5ri unless otherwise provided, v in =1.8v, vss=0v, i out =10ma, topt=25?c, and use external circuit of typical application (fig. 1). (note) i lx is gradually increased by the external inductor after lx switch is turned on. in accordance with the increase of i lx , v lx is also increased. when v lx reaches v lx lim , lx switch is turned off by lx switch protection circuit. the time period from the time at which v lx reaches v lx lim to the time at which lx switch is turned off is about 3s.
6 rh5ri ? rh5ri501b unless otherwise provided, v in =3v, vss=0v, i out =10ma, topt=25?c, and use external circuit of typical application (fig. 1). symbol item v out output voltage v in input voltage vstart start-up voltage vhold hold-on voltage i in 1 input current 1 i in 2 input current 2 i lx lx switching current i lx leak lx leakage current fosc maximum oscillator frequency maxdty oscillator duty cycle h efficiency v lx lim v lx voltage limit conditions min. typ. max. unit note 4.875 5.000 5.125 v 8v i out =1ma,v in :0 ? 2v 0.8 0.9 v i out =1ma,v in :2 ? 0v 0.7 v to be measured at v in at no load 612a to be measured at v in 25a v in =5.5v v lx =0.4v 80 ma v lx =6v,v in =5.5v 0.5 a 80 100 120 khz on (v lx l ) side 65 75 85 % 70 80 % lx switch on 0.65 0.8 1.0 v note2 v out =5.0v ( note ) i lx is gradually increased by the external inductor after lx switch is turned on. in accordance with the increase of i lx , v lx is also increased. when v lx reaches v lx lim , lx switch is turned off by lx switch protection circuit. the time period from the time at which v lx reaches v lx lim to the time at which lx switch is turned off is about 3s.
7 rh5ri ? rh5ri302b symbol item v out output voltage v in input voltage vstart oscillator start-up voltage i dd 1 supply current 1 i dd 2 supply current 2 i exth ext h output current i extl ext l output current fosc maximum oscillator frequency maxdty oscillator duty cycle conditions min. typ. max. unit note 2.925 3.000 3.075 v 8v ext at no load,v out :0 ? 2v 0.7 0.8 v ext at no load,v out =2.88v 30 50 a ext at no load,v out =3.5v 2 5 a v ext =v out C0.4v C1.5 ma v ext =0.4v 1.5 ma 80 100 120 khz v ext h side 65 75 85 % v out =3.0v unless otherwise provided, v in =1.8v, vss=0v, i out =10ma, topt=25?c, and use external circuit of typical application (fig. 2). ? rh5ri502b unless otherwise provided, v in =3v, vss=0v, i out =10ma, topt=25?c, and use external circuit of typical application (fig. 2). v out =5.0v symbol item v out output voltage v in input voltage vstart oscillator start-up voltage i dd 1 supply current 1 i dd 2 supply current 2 i exth ext h output current i extl ext l output current fosc maximum oscillator frequency maxdty oscillator duty cycle conditions min. typ. max. unit note 4.875 5.000 5.125 v 8v ext at no load,v out :0 ? 2v 0.7 0.8 v ext at no load,v out =4.8v 60 90 a ext at no load,v out =5.5v 2 5 a v ext =v out C0.4v C2 ma v ext =0.4v 2 ma 80 100 120 khz v ext h side 65 75 85 %
8 ? rh5ri303b symbol item v out output voltage v in input voltage vstart start-up voltage vhold hold-on voltage h efficiency i in 1 input current 1 i in 2 input current 2 i lx lx switching current i lx leak lx leakage current i exth ext h output current i extl ext l output current v ceh 1 ce h level 1 v cel 1 ce l level 1 v ceh 2 ce h level 2 v cel 2 ce l level 2 i ceh ce h input current i cel ce l input current fosc maximum oscillator frequency maxdty oscillator duty cycle v lx lim v lx voltage limit conditions min. typ. max. unit note 2.925 3.000 3.075 v 8v i out =1ma,v in :0 ? 2v 0.8 0.9 v i out =1ma,v in :2 ? 0v 0.7 v 70 80 % to be measured at v in 48a at no load to be measured at v in 25 a v in =3.5v v lx =0.4v 60 ma v lx =6v,v in =3.5v 0.5 a v ext =v out C0.4v C1.5 ma v ext =0.4v 1.5 ma v out 3 1.5v v out C0.4 v v out 3 1.5v 0.4 v 0.8v v out <1.5v v out C0.1 v 0.8v v out <1.5v 0.1 v ce=3v 0.5 a ce=0v C 0.5 a 80 100 120 khz on (v lx l )side 65 75 85 % lx switch on 0.65 0.8 1.0 v note v out =3.0v unless otherwise provided, v in =1.8v, v ss =0v, i out =10ma, topt=25?c, and use external circuit of typical application (fig. 3). (note) i lx is gradually increased by the external inductor after lx switch is turned on. in accordance with the increase of i lx , v lx is also increased. when v lx reaches v lx lim , lx switch is turned off by lx switch protection circuit. the time period from the time at which v lx reaches v lx lim to the time at which lx switch is turned off is about 3s. rh5ri
9 ? rh5ri503b rh5ri unless otherwise provided, v in =3v, v ss =0v, i out =10ma, topt=25?c and use external circuit of typical application (fig. 3). v out =5.0v (note) i lx is gradually increased by the external inductor after lx switch is turned on. in accordance with the increase of i lx , v lx is also increased. when v lx reaches v lx lim , lx switch is turned off by lx switch protection circuit. the time period from the time at which v lx reaches v lx lim to the time at which lx switch is turned off is about 3s. symbol item v out output voltage v in input voltage vstart start-up voltage vhold hold-on voltage h efficiency i in 1 input current 1 i in 2 input current 2 i lx lx switching current i lx leak lx leakage current i exth ext h output current i extl ext l output current v ceh 1 ce h level 1 v cel 1 ce l level 1 v ceh 2 ce h level 2 v cel 2 ce l level 2 i ceh ce h input current i cel ce l input current fosc maximum oscillator frequency maxdty oscillator duty cycle v lx lim v lx voltage limit conditions min. typ. max. unit note 4.875 5.000 5.125 v 8v i out =1ma,v in :0 ? 2v 0.8 0.9 v i out =1ma,v in :2 ? 0v 0.7 v 70 85 % to be measured at v in 612a at no load to be measured at v in 25a v in =5.5v v lx =0.4v 80 ma v lx =6v,v in =5.5v 0.5 a v ext =v out C0.4v C2.0 ma v ext =0.4v 2.0 ma v out 3 1.5v v out C0.4 v v out 3 1.5v 0.4 v 0.8v v out <1.5v v out C0.1 v 0.8v v out <1.5v 0.1 v ce=5v 0.5 a ce=0v C0.5 a 80 100 120 khz on (v lx l )side 65 75 85 % lx switch on 0.65 0.8 1.0 v note
10 operation of step-up dc/dc converter step-up dc/dc converter charges energy in the inductor when lx transistor (lxtr) is on, and discharges the energy with the addition of the energy from input power source thereto, so that a higher output voltage than the input voltage is obtained. the operation will be explained with reference to the following diagrams : < current through l > < basic circuits > rh5ri i2 l sd i out v out cl lx tr i1 v in il ilmin ilmax topen t ton toff t=1/fosc step 1 : lxtr is turned on and current il (=i1 ) flows, so that energy is charged in l. at this moment, il(=i1 ) is increased from ilmin (=0) to reach ilmax in protection to the on-time period (ton) of lxtr. step 2 : when lxtr is turned off, schottky diode (sd) is turned on in order that l maintains il at ilmax, so that current il (=i2) is released. step 3 : il (=i2) is gradually decreased, and il reaches ilmin (=0) after a time period of topen, so that sd is turned off. in the case of vfm control system, the output voltage is maintained constant by controlling the oscillator fre- quency (fosc) with the on-time period (ton) being maintained constant. in the above two diagrams, the maximum value (ilmax) and the minimum value (ilmin) of the current which flows through the inductor are the same as those when lxtr is on and also when lxtr is off. the difference between ilmax and ilmin, which is represented by ? i, is: ? i=ilmaxCilmin=v in ton/l=(v out Cv in ) topen/l .......................................... equation 1 wherein t=1/fosc=ton+toff duty (%)=ton/t 100=ton fosc 100 topen toff in equation 1,v in ton/l and (v out Cv in ) topen/l are respectively the change in the current at on, and the change in the current at off. in the vfm system, topen < toff as illustrated in the above diagram. in this case, the energy charged in the inductor during the time period of ton is discharged in its entirely during the time period of toff, so that ilmin becomes zero (ilmin=0).
11 rh5ri when lxtr is on, the energy p on charged in the inductor is provided by equation 2 as follows : p on = 0 ton (v in il (t)) dt= 0 ton (v in 2 t/l) dt =v in 2 ton 2 /(2 l) .................................................................................................... equation 2 in the case of the step-up dc/dc converter, the energy is also supplied from the input power source at the time of off. thus, p off = 0 topen (v in il (t)) dt= 0 topen (v in (v out Cv in ) t/l)dt =v in (v out Cv in ) topen 2 /(2 l) here, topen=v in ton/(v out Cv in ) from equation 1, and when this is substituted into the above equation. =v in 3 ton 2 /(2 l (v out Cv in )) ............................................................................ equation 3 input power p in is (p on +p off )/t. when this is converted in its entirely to the output. p in =(p on +p off )/t=v out i out =p out ......................................................................... equation 4 equation 5 can be obtained as follows by solving equation 4 for i out by substituting equation 2 and 3 into equation 4 : i out =v in 2 ton 2 /(2 l t (v out Cv in ) =v in 2 maxdty 2 /(20000 fosc l (v out Cv in )) ................................................... equation 5 the peak current which flows through l lxtr sd is ilmax=v in ton/l .......................................................................................................... equation 6 therefore, it is necessary that the setting of the input/output conditions and the selection of peripheral compo- nents be made with ilmax taken into consideration. selection of peripheral components the above explanation is directed to the calculation in an ideal case where it is supposed that there is no energy loss in the external components and lxsw. in an actual case, the maximum output current will be 50 to 80% of the above calculated maximum output current. in particular, care must be taken because v in is decreased in an amount corresponding to the voltage reduction caused by lxsw when il is large or v in is small. furthermore, it is required that with respect to v out , vf of the diode (about 0.3v in the case of a schottky type diode) be taken into consideration. when i lx and v lx exceed their respective ratings, use rh5ri 2b and rh5ri 3b ics with the attach- ment of an external transistor with a low saturation voltage thereto. hints
12 rh5ri typical characteristics 1) output voltage vs. output current rh5ri351b l=82? output current i out (ma) output voltage v out (v) 2.0v 3.0v 0 20 40 60 80 100 0.5 0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 1.0v v in =0.9v l=120? 2.0v 3.0v 1.0v output current i out (ma) 0 20 40 60 80 100 output voltage v out (v) 0.5 0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 v in =0.9v rh5ri501b l=82? v in =0.9v 2.0v 3.0v 4.0v 1.5v output current i out (ma) 0 20 40 60 80 100 output voltage v out (v) 1 0 2 3 4 5 6 rh5ri352b l=28? v in =0.9v 2.0v 3.0v 1.0v output current i out (ma) 0 200 400 600 output voltage v out (v) 0.5 0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 rh5ri351b rh5ri501b l=120? 2.0v 3.0v 4.0v 1.5v output current i out (ma) 0 20 40 60 80 100 output voltage v out (v) 1 0 2 3 4 5 6 v in =0.9v rh5ri502b l=28? v in =0.9v 2.0v 3.0v 4.0v 1.5v output current i out (ma) 0 200 400 600 output voltage v out (v) 1 0 2 3 4 5 6
13 rh5ri 2) efficiency vs. output current rh5ri351b l=82? 2.0v 3.0v 0 20 40 60 80 100 80 90 100 60 70 40 50 20 10 30 0 output current i out (ma) efficiency h (%) v in =0.9v 1.0v l=120? 2.0v 3.0v 0 20 40 60 80 100 output current i out (ma) 80 90 100 60 70 40 50 20 10 30 0 efficiency h (%) v in =0.9v 1.0v rh5ri501b l=82? 2.0v 3.0v 1.5v 020 40 60 80 100 output current i out (ma) 80 90 100 60 70 40 50 20 10 30 0 efficiency h (%) v in =0.9v 4.0v rh5ri352b l=28? v in =0.9v 2.0v 3.0v 1.0v 0 200 400 600 output current i out (ma) 80 90 100 60 70 40 50 20 10 30 0 efficiency h (%) rh5ri351b rh5ri501b l=120? 2.0v 1.5v 020 40 60 80 100 output current i out (ma) 80 90 100 60 70 40 50 20 10 30 0 efficiency h (%) v in =0.9v 3.0v 4.0v rh5ri502b l=28? v in =0.9v 2.0v 3.0v 4.0v 1.5v 0 200 400 600 output current i out (ma) 80 90 100 60 70 40 50 20 10 30 0 efficiency h (%)
14 rh5ri 3) output current vs.ripple voltage rh5ri351a l=82? 100 120 80 60 40 20 0 20 0 40 60 80 100 output current i out (ma) ripple voltage vr (mv p-p) v in =0.9v 2.0v 3.0v 1.5v l=120? 20 0 40 60 80 100 output current i out (ma) 100 120 80 60 40 20 0 ripple voltage vr (mv p-p) 2.0v 3.0v 1.5v v in =0.9v rh5ri501b l=82? 20 040 60 80 100 output current i out (ma) 100 120 80 60 40 20 0 ripple voltage vr (mv p-p) v in =0.9v 2.0v 4.0v 3.0v rh5ri352b l=28? 100 0 200 300 400 output current i out (ma) 100 120 140 160 180 200 80 60 40 20 0 ripple voltage vr (mv p-p) v in =0.9v 2.0v 1.5v 3.0v rh5ri351b rh5ri501b l=120? 20 0 40 60 80 100 output current i out (ma) 100 120 140 80 60 40 20 0 ripple voltage vr (mv p-p) 2.0v 4.0v 3.0v v in =0.9v rh5ri502b l=28? 200 0 400 600 output current i out (ma) 250 200 150 100 50 0 ripple voltage vr (mv p-p) v in =0.9v 2.0v 4.0v 3.0v
15 rh5ri 4) start-up/hold-on voltage vs. output current rh5ri351b l=82? 1.0 1.2 0.8 0.6 0.4 0.2 0 0 5 10 15 output current i out (ma) start-up/hold-on voltage vstart/vhold (v) vstart vhold l=82? 0 5 10 15 output current i out (ma) 1.0 1.2 1.4 1.6 0.8 0.6 0.4 0.2 0 start-up/hold-on voltage vstart/vhold (v) vstart vhold rh5ri352b l=28? 0 50 100 150 200 output current i out (ma) 2.5 2.0 1.5 1.0 0.5 0 start-up/hold-on voltage vstart/vhold (v) vstart vhold rh5ri501b 5.00 5.05 5.10 5.15 5.20 4.95 4.90 4.85 4.80 ?0 ?0 0 20 40 60 80 temperature topt(?c) output voltage v out (v) rh5ri501b rh5ri502b l=28? 0 50 100 150 200 output current i out (ma) 2.5 2.0 1.5 1.0 0.5 0 start-up/hold-on voltage vstart/vhold (v) vstart vhold rh5ri501b 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.3 0.2 0.1 0 ?0 ?0 0 20 40 60 80 temperature topt(?c) start-up voltage vstart(v) 5) output voltage vs. temperature 6) start-up voltage vs. temperature
16 rh5ri 8) supply current 1 vs.temperature rh5ri501b 0.6 0.7 0.8 0.5 0.4 0.3 0.2 ?0 ?0 020406080 temperature topt(?c) hold-on voltage vhold (v) ?0 ?0 020406080 temperature topt(?c) 40 50 60 30 20 10 0 supply current i dd1 ( ?) rh5ri501b 0.8 1.0 1.2 1.4 1.6 1.8 0.6 0.4 0.2 0 ?0 ?0 020 40 60 80 temperature topt(?c) input current i in2 ( ?) rh5ri501b ?0 ?0 0 20 40 60 80 temperature topt(?c) 0.20 0.25 0.30 0.15 0.10 0.05 0 lx leakage current i lxleak ( ?) rh5ri502b rh5ri501b ?0 ?0 020406080 temperature topt(?c) lx switching current i lx (ma) 80 100 120 140 160 180 200 60 40 20 0 rh5ri501b ?0 ?0 020 40 60 80 temperature topt(?c) maximum oscillator frequency fosc (khz) 80 100 120 140 160 60 40 20 0 7) hold-on voltage vs. temperature 12) maximum oscillator frequency vs.temperature 9) input current 2 vs.temperature 10) lx switching current vs.temperature 11) lx leakage current vs.temperature
rh5ri 17 13) oscillatar duty cycle vs. temperature 15) output current vs. temperature rh5ri501b ?0 ?0 0 20 40 60 80 temperature topt(?c) oscillator duty cycle maxdty(%) 70 80 90 100 60 50 ?0 ?0 0 20 40 60 80 temperature topt(?c) 0.70 0.75 0.80 0.85 0.90 0.95 1.00 0.65 0.60 0.55 0.50 v lx voltage limit v lxlim (v) rh5ri502b ?0 ?0 0 20 40 60 80 temperature topt(?c) ext "h" output current i exth (ma) 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0.5 0 rh5ri501b rh5ri502b ?0 ?0 0204060 80 temperature topt(?c) 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0.5 0 ext "l" output current i extl (ma) 14) vlx voltage limit vs. temperature 16) output current vs. temperature
rh5ri 18 typical applications ? rh5ri 1b v in inductor diode lx out vss v out + capacitor components inductor (l) : 82h (sumida electric co., ltd.) diode (d) : ma721 (matsushita electronics corporation, schottky type) capacitor (cl) : 22f (tantalum type) fig. 1 ? rh5ri 2b v in inductor diode out vss v out + capacitor cb rb tr ext components inductor (l) : 28h (troidal core) diode (d) : hrp22 (hitachi, schottky type) capacitor (cl) : 100f (tantalum type) transistor (tr) : 2sd1628g base resistor (rb) : 300 base capacitor (cb) : 0.01f fig. 2
rh5ri 19 ? rh5ri 3b v in inductor diode lx out vss v out + capacitor ext ce nc components inductor (l) : 82h (sumida electric co., ltd.) diode (d) : ma721 (matsushita electronics corporation, schottky type) capacitor (cl) : 22f (tantalum type) fig. 3 v in inductor diode lx out vss v out + capacitor cb rb tr ext ce nc components inductor (l) : 28h (troidal core) diode (d) : hrp22 (hitachi, schottky type) capacitor (cl) : 100f (tantalum type) transistor (tr) : 2sd1628g base resistor (rb) : 300 base capacitor (cb) : 0.01f fig. 4
rh5ri 20 v in inductor diode lx out vss v out + capacitor ext ce nc rh5ri 3b pull-up resistor tr ce ? ce pin drive circuit fig. 5
rh5ri 21 v in inductor diode out vss v out + capacitor ext zd:6.8v rh5ri502b tr cb r zd rb starter circuit (note) when the output current is small or the output voltage is unstable,use the rzd for flowing the bias current through th e zener diode zd. fig. 6 v in inductor diode out vss v out + capacitor rh5ri 1b tr pnp lx rb1 rb2 starter circuit (note) when the lx pin voltage is over the rating at the time pnp tr is off,use a rh5ri 2b and drive the pnp tr. by the external npn tr. fig. 7 application circuits ? 12v step-up circuit ? step-down circuit
rh5ri 22 v in trance1:1 diode out vss v out + capacitor lx rh5ri 1b starter circuit (note) use a rh5ri 2b,depend on the output current. fig. 8 zd st r st tr v out side v out side v in side v in side starter circuit starter circuit zdst 2.5v zd st designation of output voltage rst input bias current of zd st and tr. (several k to several hundreds k ) ? step-up/step-down circuit with flyback * the starter circuit is necessary for all above circuits. 1.for step-up circuit. 1.for step-down and step-up/step-down circuit.
rh5ri 23 when using these ics, be sure to take care of the following points : ? set external components as close as possible to the ic and minimize the connection between the com- ponents and the ic. in particular, when an external component is connected to out pin, make mini- mum connection with the capacitor. ? make sufficient grounding. a large current flows through vss pin by switching. when the impedance of the vss connection is high, the potential within the ic is varied by the switching current. this mayresult in unstable operation of the ic. ? use capacitor with a capacity of 10f or more, and with good high frequency characteristics such as tantalum capacitor. we recommend the use of a capacitor with an allowable voltage which is at least three times the output set voltage. this is because there may be the case where a spike-shaped high voltage is generated by the inductor when lx transistor is turned off. ? take the utmost care when choosing an inductor. namely, choose such an inductor that has sufficient- ly small d.c. resistance and large allowable current, and hardly reaches magnetic saturation. when the inductance value of the inductor is small, there may be the case where i lx exceeds the absolute maximum ratings at the maximum load. use an inductor with an appropriate inductance (refer to selectionof peripheral components). ? use a diode of a schottky type with high switching speed, and also take care of the rated current (refer to selection of peripheral components). the performance of power source circuits using these ics largely depends upon the peripheral components. take the utmost care in the selection of the peripheral components. in particular, design the peripheral circuits in such a manner that the values such as volt- age, current and power of each component, pcb patterns and the ic do not exceed their respective rated values. application hints

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