www.bookly.com 1 3.0a step-down converter BM1430 features ? 3 a output current ? efficiency up to nearly 90% @+5v /3a output ? +3.85v to + 23v input range ?55 a shutdown supply current ?380 khz switching freq uency ? adjustable output voltage from 1.22v to 0.85*v in ? cycle-by-cycle current limit protection ? thermal shutdown protection ? frequency fold back at short circuit ?low start up input voltage ; low dropout to nearly 0.7v ? full pin-pin with act4060/ td1410 / mp1410 ? sop-8 package applications ? tft lcd monitors ? portable dvds ? net card ?telecom power supplies ? dsl and cable modems and routers ?lcd tv general description the bm14 3 0 is a current-mode step-down dc-dc converter that generates up to 3 a output current at 380khz switching frequency. the device utilizes advanced bcd process for operation with input voltage up to + 23v c onsuming only 5 5a in shutdown mode, the bm143 0 is highly efficient with peak efficiency at 9 0 % when in operation. protection features include cycle-by-cycle current limit, t hermal shutdow n, and frequency fold back at short circuit. the bm143 0 is available in sop-8 package and requires very few external devices for operation. it can replace td1410 /mp 9141 without change external components and pcb layout. if vin is over 12v, if not use pin7 function , can pull-up a 100k ohm to vin input with a pull-up resistor, b e better not short to vin dirrectly. figure 1. typical application circuit (cff= 0 ~ 33nf) figure4. xl1583 typical applic ation circuit 12v-5v/3a www.datasheet.co.kr datasheet pdf - http://www..net/
www.bookly.com 2 BM1430 ordering information part number temperature range package BM1430 -40 c to 85 c sop-8 pin configuration pin no. pin name pin description 1 n/c bootstrap. this pin acts as the positive rail for the high-side switch?s gate driver . connect a 10nf between this pin and sw. 2 in input supply. bypass this pin to g with a low esr capaci tor. see input capacitor in application information section. 3 sw switch output. connect this pin to the switching end of the inductor. 4 g ground. 5 fb feedback input. the voltage at this pin is regulated to 1.2 2 v. connect to the resist or divider bet ween output and ground to set output voltage. 6 n/c compensation pin. see compensation tec hnique in application information section. 7 en enable input. when higher than 1. 7 v, this pin turns the ic on. when lower than 0.8 v, this pin turns the ic off. output voltage is discharged when the ic is off. this pin has a small internal pull up current to a high level voltage when pin is not connected. 8 n/c not connected. 3 4 2 5 6 7 8 1 n/c in sw gnd n/c en n/c BM1430 fb www.datasheet.co.kr datasheet pdf - http://www..net/
www.bookly.com 3 BM1430 absolute maximum ratings (note: do not exceed these limits to prevent damage to the device. exposure to absolute maximu m rating conditions for long peri ods may affect device reliability.) parameter value unit in supply voltage -0.3 to 23 v sw voltage -1 to vin + 1 v bs voltage vsw - 0.3 to vsw + 6 v en, fb, voltage -0.3 to 10 v continuous sw current internally limited a junction to ambient thermal resistance ( ja ) 105 c/w operating junction temperature -40 to 150 c storage temperature -55 to 150 c lead temperature (soldering, 10 sec) 300 c electrical charcxeristics (vin = 12v, tj = 25 q c unless otherwise specified) parameter symbol test conditions min typ max unit feedback voltage vfb +5v vin 20v, vcomp = 1.5v 1.2 1.22 1.23 v high-side switch on resistance ronh 0.20 ? low-side switch on resistance ronl 4.7 ? sw leakage ven = 0 0.5 5 a current limit ilim 3.6 4.2 a comp to current limit transconductance gcomp 1.8 a/v error amplifier transconductance gea ? icomp = 10a 550 a/v error amplifier dc gain avea 3200 v/v switching frequency fsw 320 380 430 khz short circuit switching frequency vfb = 0 8 0 khz maximum duty cycle dmax vfb = 1.1v 100 % minimum duty cycle vfb = 1.4v 0% enable threshold voltage hysteresis = 0.1v 0.8 2 v enable pull up current pin pulled up to 4.5v typically when left unconnected 1 5 a supply current in shutdown ven = 0 55 6 0 a ic supply current in operation ven = 3v, vfb = 1.4v 6 ma thermal shutdown temperature hysteresis = 10c 140 c www.datasheet.co.kr datasheet pdf - http://www..net/
www.bookly.com 4 BM1430 figure 2 . functional block diagram functional description as seen in figure 2, functional block diagram , the BM1430 is a current mode pulse width modulation (pwm) converter. the converter operates as follows: a switching cycle starts when the rising edge of the oscillator clock output causes the high-side power switch to turn on and the low-side power switch to turn off. with the sw side of the inductor now connected to in, the inductor current ramps up to store energy in the its magnetic field. the inductor current level is measured by the current sense amplifier and added to the oscillator ramp signal. if the resulting summation is higher than comp internal voltage, output of the pwm comparator goes high. when this happens or when oscillator clock output goes low, the high-side power switch turns off and the low-side power switch turns on. at this point, the sw side of the inductor swings to a diode voltage below ground, causing the inductor current to decrease and magnetic energy to be transferred to output. this state continues until the cycle starts again. the high-side power switch is driven by logic using internal bootstrap as the positive rail. the pin is charged to v sw + 6v when the low-side power switch turns on. the comp voltage is the integration of the error between fb input and the internal 1.2 2 v reference. if fb is lower than the reference voltage, comp tends to go higher to increase current to the output. current limit happens when comp reaches its maximum clam value of 2.55v. the oscillator normally swit ches at 38 0khz. however, if fb voltage is less than 0.7v, then the switching frequency decreases until it reaches a minimum of 8 0khz at v fb = 0.5v. shutdown control the BM1430 has an enable input en for turning the ic on or off. when en is less than 1.8v, the ic is in 55 a low current shutdown mode and output is discharged through the low-side power switch. when en is higher than 1.85v, the ic is in normal operation mode. en is internally pulled up with a 1 5a current source and can be left unconnected for always-on operation. note that en is a low voltage input with a maximum voltage of 10 v; it should never be directly connected to vin if over 12v input. thermal shutdown the BM1430 automatically turns off when its junction temperature exceeds 1 40c. function block figure3. function block diagram of xl1583 typical application circuit www.datasheet.co.kr datasheet pdf - http://www..net/
www.bookly.com 5 BM1430 application information output voltage setting fb vout r fb1 r fb2 figure 3. output voltage setting figure 3 shows the connections for setting the output voltage. select the proper ratio of the two feedback resistors r fb1 and r fb2 based on the output voltage. typically, use r fb2 10k ? and determine r fb1 from the output voltage: 12 1 1.225 out fb fb v rr v ?? =? ?? ?? (1 ) inductor selection the inductor maintains a continuous current to the output load. this inductor current has a ripple that is dependent on the inductance value: higher inductance reduces the peak-to-peak ripple current. the trade off for high inductance value is the increase in inductor core size and series resistance, and the reduction in current handling capability. in general, select an inductance value l based on ripple current requirement: () out in out in sw outmax ripple vvv l vf i k ?? = (2 ) where v in is the input voltage, v out is the output voltage, f sw is the switching frequency, i outmax is the maximum output current, and k ripple is the ripple fcxor. typically, choose k ripple = 30% to correspond to the peak-to-peak ripple current being 30% of the maximum output current. with this inductor value (table 1), the peak inductor current is iout ? (1 + kripple / 2). make sure that this peak inductor current is less that the 4 a current limit. finally, select the inductor core size so that it does not saturate at 3a. table 1. typical inductor values vout 1.5v 1.8v 2.5v 3.3v 5v 12v l(h) >=6.8 >=6.8 >=10 >=15 >=22 >=47 input capacitor the input capacitor needs to be carefully selected to maintain sufficiently low ripple at the supply input of the converter. a low esr capacitor is highly recommended. since large current flows in and out of this capacitor during switching, its esr also affects efficiency. the input capacitance needs to be higher than 10f. the best choice is the ceramic type; however, low esr tantalum or electrolytic types may also be used provided that the rms ripple current rating is higher than 50% of the output current. the input capacitor should be placed close to the in and g pins of the ic, with shortest traces possible. in the case of tantalum or electrolytic types, they can be further away if a small parallel 0.1f ceramic capacitor is placed right next to the ic. output capacitor the output capacitor also needs to have low esr to keep low output voltage ripple. the output ripple voltage is: v ripple = i outmax k ripple r esr 2 28 in s w out v flc + ( 3 ) where i outmax is the maximum output current, k ripple is the ripple fcxor, r esr is the esr resistance of the output capacitor, f sw is the switching frequency, l in the inductor value, c out is the output capacitance. in the case of ceramic output capacitors, r esr is very small and does not contribute to the ripple. therefore, a lower capacitance value can be used for ceramic type. in the case of tantalum or electrolytic type, the ripple is dominated by r esr multiplied by the ripple current. in that case, the output capacitor is chosen to have sufficiently low esr. for ceramic output type, typically choose a capacitance of about 22f. for tantalum or electrolytic type, choose a capacitor with less than 50m ? esr. rectifier diode use a schottky diode as the rectifier to conduct current when the high-side power switch is off. the schottky diode must have current rating higher than the maximum output current and the reverse voltage rating higher than the maximum input voltage. www.datasheet.co.kr datasheet pdf - http://www..net/
www.bookly.com 6 BM1430 8: 6 : 9: 7 : typecial performance and characteristics: schottky diode selection table current surface mount through hole vr (the same as system maximum input voltage) 20v 30v 40v 50v 60v 1a 1n5817 sk14xx 1n5819 1n5820 1n5821 1n5822 mbr320 mbr330 mbr340 mbr350 mbr360 sk32 sk33 sk34 sk35 sk36 30wq03 30wq04 30wq05 31dq03 31dq04 31dq05 3a sr302 sr303 sr304 sr305 sr306 www.datasheet.co.kr datasheet pdf - http://www..net/
www.bookly.com 7 BM1430 package outline sop-8 package outline and dimensions dimension in milimeters dimension in inches symbol min max min max a 1.350 1.750 0.053 0.069 a1 0.100 0.250 0.004 0.010 a2 1.350 1.550 0.053 0.061 b 0.330 0.510 0.013 0.020 c 0.190 0.250 0.007 0.010 d 4.780 5.000 0.188 0.197 e 3.800 4.000 0.150 0.157 e1 5.800 6.300 0.228 0.248 e 1.270 typ 0.050 typ l 0.400 1.270 0.016 0.050 0 8 0 8 figure10 : figure11: www.datasheet.co.kr datasheet pdf - http://www..net/
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