tiny package high efficiency step-up dc/dc converter ? introduction the LR9908 is a cmos step-up switching dc/dc conver ter that mainly consists of a refer ence voltage source, an oscillator, and a comparator. the LR9908 allows the duty ratio to be automatically switched according to the load (light load: 66%, high output current: 78%), enabling products with a low ripple over a wide range, high efficiency, and high output current. with the LR9908, a step-up switching dc/dc converter can be configured by using an external coil, capacitor, diode and nmos. this feature, along with the mini package and low current consumption, makes the LR9908 ideal for applications such as the power suppl y unit of portable equipment. ? applications ? pda ? dsc ? lcd panel ? rf-tags ? mp3 ? portable instrument ? wireless equipment ? features ? low voltage operati on: oscillation start voltage at 0.8v ? duty ratio: 66/78%, built-in auto switching ? external parts: coil, capacitor, diode, nmos ? high efficiency 85% typ. ? output voltage adjustable ? providing flexibility for using external power switches ? zero shutdown mode supply current ? 6a quiescent (switch-off) supply current ? small sot23-5,sot89-5 package ? ordering information LR9908 LR9908 leshan radio company, ltd. 1/8
? block diagrams ? pin assignment pin no. sot23-5 pin name functions 1 1 fb feedback input pin 2 2 v dd ic power supply pin - 3 en chip enable (active high) 3 - nc no connection 4 4 v ss gnd pin 5 5 ext external transistor connection pin pin no. sot89-5 pin name functions - 1 en chip enable (active high) 1 - nc no connection 2 2 v dd ic power supply pin 3 3 fb feedback input pin 4 4 ext external transistor connection pin 5 5 v ss gnd pin LR9908 LR9908a LR9908b LR9908a LR9908b leshan radio company, ltd. 2/8
? absolute maximum ratings (unless otherwise specified, ta= ? 2 5 ) parameter symbol ratings unit v out pin voltage v out v ss 0.3 ~ v ss 8 v en pin voltage en v ss 0.3 ~ v ss 8 v power dissipation sot-23-5 pd 250 mw sot-89-5 500 mw operating temperature topr 40 ~ 85 storage temperature tstg 40 ~ 125 ? electrical characteristics (unless otherwise specified, ta = ? 2 5 ) parameter symbol conditions min. typ. max. unit feedback voltage v fb v fb(s) 0.98 v fb v fb(s) 1.02 v input voltage v in 8 v oscillation start voltage v st no external parts, voltage applied to v out lx pulled up to v out via 300 resistor 0.8 v current consumption 1 i ss1 v cc =5v, continuously switching 30 40 a current consumption 2 i ss2 v cc =5v, fb=2.5v, no switching 5 10 a shut down current i sss v cc =5v,v en =0 v 0.5 a line regulation ? v out1 v in = 0.4v out 0.6v out v out =5v 20 50 mv load regulation ? v out2 i out = 10 a ~ 50ma v out =5v 20 50 mv oscillation frequency f osc 100 khz duty ratio 1 duty1 v out = 0.95v out measure waveform at lx pin 70 78 85 % duty ratio 2 duty2 measure waveform at lx pin with light load 66 % efficiency effi 85 % shutdown pin input voltage v sh v out =0.95v out judge oscillation at ext pin 0.75 v v sl1 v out = 0.95v out judge stop at ext pin 0.3 v shutdown pin input current i sh v en 8v 0.1 a i sl v en 0v 0.1 a remark 1 v in =v out(s) ? 0.6 applied, i out = ? v out(s) / 250 ? 2 shutdown function built-in type: en pin is connected to v out 3 v out(s) specified above is the se t output voltage value, and v out is the typical value of the actual output voltage. leshan radio company, ltd. 3/8
standard circuits component: inductor 22uh(sumida) diode in5817 in5819 capacitor 47uf (tantalum type) mos ce2312 xp151 xp161 r fb set up so that r fb1 /r fb2 = v out v fb /v fb v out =set-up output voltage , please use with r fb1 +r fb2 2m ? c fb set up that fzfb=1/(2 c fb r fb1 ) is within the adjustments necessary in respect of l,c l . 1 cle9908 circuits 1:(v in 3v) 2 ce9908 circuits 2:(v in 3v) LR9908 LR9908 leshan radio company, ltd. 4/8
characteristics a. v out vs i out v out 5.5v b. efficiency vs i out v out 5.5v leshan radio company, ltd. 5/8
c. v out vs i out v out 12v d. efficiency vs i out v out 12v leshan radio company, ltd. 6/8
e. v out vs i out v out 18v f. efficiency vs i out v out 18v leshan radio company, ltd. 7/8
? package information sot- 23- 5 sot- 89- 5 leshan radio company, ltd. 8/8
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