64 ics 1-1-3 dc/dc converter ics SI-8511NVS surface-mount, synchronous rectifier step-down switching mode control ics features surface-mount package (tssop24) high efficiency due to synchronous rectifica- tion: 92% (at v in = 5v, i o = 1a, v o = 2.5v) capable of downsize a choke-coil due to ic's high switching frequency (400khz typ, on t ime control). (compared with conventional sanken devices) low reference voltage (v ref ) of 1.1v. the output voltage is variable from 1.1v to 6v. high-speed response to a load compatible with low esr capacitors soft start and output on/off available built-in overcurrent and output-overvoltage protection circuits pwrgd function to indicate the output voltage status high precision reference voltage: 1.1v 1.2% absolute maximum ratings unit v v v v v c c ratings 7 25 30 v cc 7 +150 ?0 to +150 symbol v cc v in v h v en v pwrgd t j t stg parameter control-system dc input voltage dc input voltage boost block input voltage en terminal input voltage pwrgd terminal applied voltage junction temperature storage temperature (t a =25 c) recommended operating conditions parameter control system input voltage range input voltage range output voltage range operating temperature range symbol v cc v in v o t op unit v v v c ratings 4.5 to 5.5 3 to 18 1.1 to 6 ?0 to +85 electrical characteristics (t a =25 c unless otherwise specified) unit v mv/ c ma ma a a v v s s v a ? ? ? ? v a a v v a v v v a a symbol v o ? v o / ? t i op i op i std1 i std2 v uvlo1 v uvlo2 t on t off v ref i ref ronhh ronhl ronlh ronll vh-vlin i lim i ss v celo v cehi ice v sens v sens v pwrgd i pwrgd i pwrgd ratings min. typ. max. ?.2% 1.1 +1.2% 0.03 6 1 100 50 3.7 4.45 2.5 2.9 1.27 0.7 1.1 1.2 1.3 100 5.5 5.5 5.5 5.5 4.5 5 5.5 90 100 110 20 0 0.8 2.4 v cc 5 1.32 0.88 0.4 120 5 conditions v in =5v, v cc =5v, vsns connected to vo, i o =0a v in =5v, v cc =5v, vsns connected to vo, i o =0a, t a =0 to 85 c v cc =5v, en=h, fadj:open v in =5v, en=h v cc =5v, en=l v in =5v, en=l v in =5v v cc =5v v cc =5v, v in =5v, v o =2.5v v cc =5v v cc =5v v cc =5v vh-vlin=5v vh-vlin=5v v cc =5v v cc =5v v cc =5v, v in =5v v cc =5v v cc =5v v cc =5v v cc =5v, en=5v v cc =5v v cc =5v v cc =5v, ipwrgd=120 a v cc =5v, vpwrgd=0.4v vpwrgd=5v applications power supplies for notebook pcs and mobile devices onboard local power supplies ? a equipment for stabilization of the secondary-side output voltage of switching power supplies dynamic characteristics circuit current undervoltage lockout on time control high side drive low side drive bootstrap protection system parameter output voltage t emperature coefficient of output voltage circuit current (v cc te r m inal) circuit current (v in t erminal) standby current 1 (v cc t erminal) standby current 2 (v in t erminal) uvlo operating voltage 1 (v cc t erminal) uvlo operating voltage 2 (v in t erminal) on time minimum off time ref terminal voltage ref terminal source current on resistance (high side) on resistance (low side) on resistance (high side) on resistance (low side) bootstrap voltage current for current limit detection soft start terminal current en low level voltage en high level voltage en bias level current pwrgd good voltage (high side) pwrgd good voltage (low side) pwrgd low output voltage pwrgd terminal current pwrgd leakage current
65 ics SI-8511NVS external dimensions (tssop24) (unit : mm) block diagram (pin assignment) 0 to 10 (6.4) 13 11 11 12 24 1 7.6 0.2 1.15 0.05 0.4 0.10 0.05 0.50 0.2 1.90 3.00 7.9 0.2 7.80 0.1 0.375 typ 0.65 5.60 0.1 a 0.22 +0.1 ?.05 0.15 + 0 .1 0 .0 5 0.12 a m 11 11 0.08 s s 1 1 1 1 1 1 1 1 depth 0.02 to 0.08 2.0 mirror surface depth 0.02 to 0.08 1.0 mirror surface v in ilim v in fadj fset ss skip open : skip mode l : no skip mode v cc 2 v cc 1 +5v v o v o isen vh drvh lin drvl pgnd v o vsns ovp_sl 12 14 level shift latch buff logic osc buff comp + + synchronous cont. (logic) uvlo gate driver off clamp pre_reg vpreg pwrgd en en h : on l : off power_good h : good l : ng gnd power good switching constant on time cont. open : change frequency short : 400khz operation + + + ocp ss t ypical connection diagram + nc r1 5m ? r5 10 ? r6 10 ? r4 47k ? r12 r13 c3 0.1 f d1 sjpj-l3 r11 : 100k ? r8 : 200k ? c8 : 220pf c4 : 3.3 q2 f v cc en skip c2 : 330 f v o v in q1 r2 c9 1000 pf r10 2.2k ? pwrgd v cc r7 47k ? r9 c6 0.1 ~ 1 f d2 : sfpl52 l1 : 10 h v cc : 5v c1 : 10 f c5 : 4.7 f c7 : 0.1 f SI-8511NVS 24 lin 23 drvl 22 pgnd 21 v cc 2 20 ovp_sl 19 v cc 1 18 ss 17 en 16 skip 15 fadj 14 nc 13 nc 1 drvh 2 vh 3 v in 4 isen 5 ilin 6 gnd 7 vsns 8 v o 9 pwrgd 10 ref 11 nc 12 plastic mold package type flammability: ul94v-0 product mass: approx. 1.36g mos fet q 1 , q 2 be sure to use logic type mos fet as q 1 and q 2 . if you use a normal power mos fet type, the on resistance may not drop to a satisfactory level due to a shortage of v gs . this may deteriorate the efficiency and cause overheating. diode d 1 be sure to use a schottky-barrier diode for d 1 . if other diodes like fast recovery diodes are used, ic may be destroyed because of the reverse voltage generated by the recovery voltage or on voltage. choke coil l 1 if the winding resistance of the choke coil is too high, the efficiency may drop below the rated value. ? ake care concerning heat radiation from the choke coil caused by magnetic saturation due to overload or short-circuit load. capacitor c 1 , c 2 as large ripple currents flow through c 1 and c 2 , use high-frequency and low- impedance capacitors suitable for switching mode power supplies. especially when the impedance of c 2 is high, the switching waveform may become abnor- mal at low temperatures. for c 2 , do not use a capacitor with an extremely low equivalent series resistance (esr) such as a ceramic capacitor, which may cause an abnormal oscillation. *t o create the optimum operating conditions, place the components as close as possible to each other.
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