1/9 L5972D may 2002 n 2a internal switch n operating input voltage from 4.4v to 36v n output voltage adjustable from 1.235v to 35v n low dropout operation: 100% duty cycle n 250khz internally fixed frequency n voltage feedforward n zero load current operation n internal current limiting n protection against feedback disconnection n thermal shutdown applications: n consumer: stb, dvd, tv, vcr,car radio, lcd monitors n networking: xdsl, modems,dc-dc modules n computer: printers, audio/graphic cards, optical storage, hard disk drive n industrial: chargers, car battery dc-dc converters description the L5972D is a step down monolithic power switch- ing regulator with a minimum switch current limit of 2a so it is able to deliver more than 1.5a dc current to the load depending on the application conditions. the output voltage can be set from 1.235v to 35v. the device uses an internal p-channel d-mos tran- sistor (with a typical rdson of 250m w ) as switching element to minimize the size of the external compo- nents. an internal oscillator fixes the switching frequency at 250khz. having a minimum input voltage of 4.4v only, it is particularly suitable for 5v bus, available in all com- puter related applications. pulse by pulse current limit with the internal frequen- cy modulation offers an effective constant current short circuit protection. so8 (4+2+2) ordering numbers: L5972D (so8) L5972D013tr (tape & reel) 2a switch step down switching regulator test application circuit vinmax = 35v c1 10 f 35v ceramic d1 stps2l25u vcc comp gnd out fb 1 3 7 5 6 4 8 2 r3 4.7k l1 22 h coilcraft r1 5.6k r2 3.3k c3 22nf c4 san y o poscap 100 f 10v L5972D vout=3.3v c2 220pf m m m
L5972D 2/9 pin connection pin description thermal data (*) package mounted on board (4cm 2 ground-plane) absolute maximum ratings n pin function 1 out regulator output. 2,3,6,7 gnd ground. 4 comp e/a output for frequency compensation. 5 fb feedback input. connecting directly to this pin results in an output voltage of 1.23v. an external resistive divider is required for higher output voltages. 8 vcc unregulated dc input voltage. symbol parameter value unit r th (j-amb) thermal resistance junction to ambient max. 65 (*) c/w symbol parameter value unit v 8 input voltage 40 v v 1 out pin dc voltage out pin peak voltage at d t = 0.1 m s -1 to 40 -5 to 40 v v i 1 maximum output current int. limit. v 4 , v 5 analog pins 4 v p tot power dissipation at tamb 70c 1.2 w t j operating junction temperature range -40 to 150 c t stg storage temperature range -55 to 150 c out gnd gnd comp 1 3 2 4 vcc gnd gnd fb 8 7 6 5 d02in1367
3/9 L5972D electrical characteristics (t j = 25c, v cc = 12v, unless otherwise specified.) (*) specification referred to tj from -40 to 125c. symbol parameter test condition min. typ. max. unit v cc operating input voltage range v o = 1.235v; i o = 1.5a * 4.4 36 v v d dropout voltage v cc = 4.4v; i o = 1.5a * 0.375 0.75 v i l maximum limiting current v cc = 4.4v to 36v * 2 2.5 3 a f s switching frequency * 212 250 280 khz 225 250 275 khz duty cycle 0 100 % dynamic characteristics (see test circuit ). v 5 voltage feedback 4.4v < v cc < 36v, 20ma < i o < 1.5a 1.220 1.235 1.25 v * 1.198 1.235 1.272 v h efficiency v o = 5v, v cc = 12v 90 % dc characteristics i qop total operating quiescent current * 3 5 ma i q quiescent current duty cycle = 0; v fb = 1.5v 2.5 ma error amplifier v oh high level output voltage vfb = 1v 3.5 v v ol low level output voltage vfb = 1.5v 0.4 v i o source source output current v comp = 1.9v; v fb = 1v 200 300 m a i o sink sink output current v comp = 1.9v; v fb = 1.5v 1 1.5 ma i b source bias current 2.5 4 m a dc open loop gain r l = 50 65 db gm transconductance i comp = -0.1ma to 0.1ma v comp = 1.9v 2.3 ms
L5972D 4/9 figure 1. output voltage vs. junction temperature figure 2. line regulation figure 3. output voltage vs. junction temperature figure 4. quiescent current vs. junction figure 5. shutdown current vs.junction temperature figure 6. switching frequency vs.junction temperature 3.276 3.28 3.284 3.288 3.292 3.296 3.3 3.304 3.308 3.312 00.511.5 io ( a ) vo (v) t j = 125c t j = 25c vcc = 12v vo = 3.3v 3.276 3.28 3.284 3.288 3.292 3.296 3.3 3.304 3.308 3.312 010203040 vcc (v) tj = 125c tj = 25c vcc = 12v vo = 3.3v vo (v) t j (c) vcc=12v 1.2 1.21 1.22 1.23 1.24 1.25 -50 0 50 100 150 vo (v) vcc = 12v 1.2 1.4 1.6 1.8 2 -50 050 100 150 tj (c) iq (ma) vcc = 12v dc = 0% 30 40 50 60 70 -50 0 50 100 150 ishd ( m a) vcc = 12v tj (c) 1.2 1.4 1.6 1.8 2 -50 050 100 150 tj (c) i q ( ma ) vcc = 12v dc = 0%
5/9 L5972D application circuit in figure 7 is shown the demo board application circuit for the device in smd version, where the input supply voltage, vcc, can range from 4.4v to 25v due to the rated voltage of the input capacitor and the output voltage is adjustable from 1.235v to v cc . figure 7. demo board application circuit table 1. component list reference part number description manufacturer c1 10 m f, 25v tokin c2 10tpb100m 100 m f, 10v sanyo, poscap c3 c1206c223k5rac 22nf, 10%, 50v kemet c4 c1206c221j5gac 220pf, 5%, 50v kemet r1 5.6k, 1%, 0.25w neohm r2 3.3k, 1%, 0.25w neohm r3 2.7k, 1%, 0.25w neohm d1 stps2l25u 2a, 25v st l1 do3316p-333 33 m h, 2.1a coilcraft vinmax=25v c1 10uf 25v tokin d1 stps2l25u vcc comp gnd out fb 1 3 7 5 6 4 8 2 r3 4.7k l1 33uh coilcraft r1 5.6k r2 3.3k c3 22nf c4 san y o poscap 100uf 10v L5972D vout=3.3v c2 220pf
L5972D 6/9 figure 8. pcb layout (component side) 42mm 34mm figure 9. pcb layout (bottom side) figure 10. pcb layout (front side) sideways two graphs show the tj versus output cur- rent in different conditions of the input and output voltage. figure 11. junction temperature vs. output current figure 12. junction temperature vs. output current 20 30 40 50 60 70 80 90 100 110 120 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 io (a) tj(c) vcc = 5v tamb = 25c vo = 3.3v vo = 1.8v vo=2.5v 20 30 40 50 60 70 80 90 100 110 120 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 io(a) tj(c) vo=5v vo=3.3v vo=2.5v vcc=12v ta m b = 2 5 c vcc=12v ta m b = 2 5 c
7/9 L5972D application ideas figure 13. positive buck-boost regulator figure 14. buck-boost regulator figure 15. dual output voltage with auxiliary winding vin=5v c1 10uf 10v ceramic d1 stps2l25u vcc comp gnd out fb L5972D 1 3 7 5 6 4 8 2 r3 4.7k l1 33uh r1 5.6k r2 3.3k c3 22nf c4 100uf 16v vout=12v/0.45a c2 220pf d2 stps2l25u m1 stn4ne03l vin=5v c1 10uf 10v ceramic d1 stps2l25u vcc comp gnd out fb L5972D 1 3 7 5 6 4 8 2 r3 4.7k l1 33uh r1 5.6k r2 3.3k c4 22nf c5 100uf 16v vout=-12v/0.45a c3 220pf c2 10uf 25v ceramic vin=12v c1 10uf 25v d1 stps2l25u vcc comp gnd out fb L5972D 1 3 7 5 6 4 8 2 r3 4.7k c3 22nf c4 100uf 10v vout=3.3v c2 220pf vout1=5v 50ma d2 stps2l25u c5 47uf 10v n1 n2 n=n1/n2=2
L5972D 8/9 dim. mm inch min. typ. max. min. typ. max. a 1.75 0.069 a1 0.1 0.25 0.004 0.010 a2 1.65 0.065 a3 0.65 0.85 0.026 0.033 b 0.35 0.48 0.014 0.019 b1 0.19 0.25 0.007 0.010 c 0.25 0.5 0.010 0.020 c1 45 (typ.) d (1) 4.8 5.0 0.189 0.197 e 5.8 6.2 0.228 0.244 e 1.27 0.050 e3 3.81 0.150 f (1) 3.8 4.0 0.15 0.157 l 0.4 1.27 0.016 0.050 m 0.6 0.024 s8 (max.) (1) d and f do not include mold flash or protrusions. mold flash or potrusions shall not exceed 0.15mm (.006inch). so8 outline and mechanical data
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