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rev 1.0 preliminary and all contents are subject to change without prior notice ? seaward electronics inc., 2 014 . ? www.seawardinc.com .cn ? page 1 se 2490 2.8a wide - input sensorless cc/cv step - down dc/dc converter typica l application description SE2490 is a wide input voltage, high efficiency active cc step - down dc/dc converter that operates in either cv (constant output voltage) mode or cc (constant output current) mode. SE2490 consists of step - down switching regulator with pwm cont rol. the device includes a reference voltage source, oscillation circuit, error amplifier and etc. SE2490 provides low - ripple power, high efficiency, and excellent transient characteristics. the pwm control circuit is able to the duty ratio linearly forms 0 up to 90%. an over current protection function is built outside that it can set by a resistance. an external compensation is easily to system stable; the low esr output capacitor can be used. with the addition of an internal n - channel power mos, a coil, capacitors, and a diode connected externally, these ics can function as step - down switching regulators. they serve as ideal power supply units for portable devices when coupled with the p sop - 8 packages, providing such outstanding featu res as low current co nsumption. since this converter can accommodate an input voltage up to 36v. features ? input voltage 8v to 36v ? vout accuracy (v fb =1v) 2% ? cc/cv mode(constant current and constant voltage) ? up to 2.8a output current ? 3%/5%/15%current limit accuracy ? duty ratio 0% to 90% pwm control ? oscillation frequency 250khz ? thermal shutdown function. ? short circuit protect (scp). ? built - in internal lx n - channel mos. ? current mode non - synchronous pwm converter ? external current limit setting. ? over voltage protection5.8v. ? built in adjustable line - compensation. ? p sop - 8 pb - free package application ? car charger ? portable charger device.
rev 1.0 preliminary and all contents are subject to change without prior notice ? seaward electronics inc., 2 014 . ? www.seawardinc.com .cn ? page 2 se 2490 2.8a wide - input sensorless cc/cv step - down dc/dc converter pin configuration pi n description pin pin function description pin pin function description bs bootstrap pin. this provides power to the internal high - side mosfet gate driver. connect a 0. 1uf capacitor from bs pin to lx pin. fb output voltage feedback control lx power switching output to external inductor. comp error amplifier output. this pin is used to compensate the co nverter. sense1 current sense input1 vin power supply input. bypass this pin with a 0.1uf ceramic capacitor to gnd, placed as close to the ic as possible. sense2 current sense input 2 gnd gnd pin. orderin g information part number marking information pa ckage remarks se 2490 - l f se 2490 yyww - l f psop - 8 yyww means production batch xx=lf: lead free.
rev 1.0 preliminary and all contents are subject to change without prior notice ? seaward electronics inc., 2 014 . ? www.seawardinc.com .cn ? page 3 se 2490 2.8a wide - input sensorless cc/cv step - down dc/dc converter functiona l block diagram absolute maximum rating parameter value units input supply voltage 40 v lx voltage - 1 to v in +1 v bs voltage v lx - 0.3 to v lx +7 v v fb ,v sense1 ,v sense2 ,v comp - 0.3 to 6 v thermal resistance from junction to case 15 /w thermal resistance from junction to ambient 40 /w operating rating parameter value units junction temperature - 4 0 150 storage temperature - 55 1 50 lead tempe rature (soldering, 10 sec) 300 5
rev 1.0 preliminary and all contents are subject to change without prior notice ? seaward electronics inc., 2 014 . ? www.seawardinc.com .cn ? page 4 se 2490 2.8a wide - input sensorless cc/cv step - down dc/dc converter electrical characteristics v in = 12 v; t j = 25c; unless otherwise specified . symbol parameter conditions min typ max unit vin input voltage 8 -- 36 v ovp detect voltage internal define - 5.8 - v ovp hysteresis - 0.3 v i ccq quiescent current v fb = 1.5v, force driver off - 2 - ma standby supply current v0 = 5v, no load - 10 15 ma i fb line compensation current v sense1 - v sense2 =100mv 3.5 5 6.5 ua v fb feedback voltage 0.98 1 1.02 v r dson high - side switch on res istance v in =12v, i out = 1a - 150 200 m r dson low - side switch on resistance v in =12v - 5 - f osc switching frequency i out =200ma 200 250 300 khz maximum duty cycle 87 90 - % minimum on - time - 150 - ns secondary cycle - by - cycle current limit minimum duty cycle, no cc - 3.5 - a v scp r eference voltage of the short circuit fold back comparator - 0.4 0.45 v v sense sense voltage(bin1) v sense1 - v sense2 97 100 103 mv v sense sense voltage(bin2) v sense1 - v sense2 95 100 105 mv v sense sense voltage(bin3) v sense1 - v sense2 85 100 115 mv t sd ther mal shutdown temp - 140 - c t sh thermal shutdown hysteresis - 30 - c
rev 1.0 preliminary and all contents are subject to change without prior notice ? seaward electronics inc., 2 014 . ? www.seawardinc.com .cn ? page 5 se 2490 2.8a wide - input sensorless cc/cv step - down dc/dc converter applications cv/cc loop regulation as seen in functional block diagram, the SE2490 is a peak current mode pulse width modulation (pwm) converter with cc and cv control. 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. with the lx side of the inductor now connected to sense1, the inductor current ramps up to sto re energy in the 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 the comp voltage, the output of the pwm comparator goes high. when thi s happens or when oscillator clock output goes low, the high - side power switch turns off. at this point, the lx 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 bs as the positive rail. this pin is charged to v lx + 5v when the low - side power switch turns on. the comp voltage is the integration of the e rror between fb input and the internal 1v reference. if fb is lower than the reference voltage, comp tends to go higher to increase current to the output. output current will increase until it reaches the cc limit set by the r1 resistor. at this point, the device will transition from regulating output voltage to regulating output current, and the output voltage will drop within creasing load. current limit protection the current limit is set by outside resistance (r sense ), when the sense1 - sense2 voltage lar ger than 100mv,the current limit is happened that driver can be turned off. the current limit set according to the following equation: output over - voltage protection the SE2490 provides output over - voltage protection function. when output over - voltage ha ppens (v sens2> 5.8v), the SE2490 shuts down. when output over - voltage is released (v sens2< 5.7v), the SE2490 recovers to normal state automatically. output short - circuit protection the SE2490 provides output short - circuit protection function. when v out is sh ort (v fb <0.4v), the auto restart function can be started that restart the regulator cycle by cycle. the cycle time is set by internal counter. t1 = 3m(sec) t2 = 90m(sec)
rev 1.0 preliminary and all contents are subject to change without prior notice ? seaward electronics inc., 2 014 . ? www.seawardinc.com .cn ? page 6 se 2490 2.8a wide - input sensorless cc/cv step - down dc/dc converter thermal shutdown the SE2490 disables switching w hen its junction temperature exceeds 140c and resumes when the temperature has dropped by 30c. output voltage setting figure1 output voltage setting figure 1 shows the connections for setting the output voltage. select the proper ratio of the two feedb ack resistors rfb1 and rfb2 based on the output voltage. typically, use rfb2 10k and determine rfb1 from the following equation: 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 gene ral, select an inductance value l based on ripple current requirement: where vin is the input voltage, v out is the output voltage, f lx is the switching frequency, i outmax is the maximum output current, and k ripple is the ripple factor. typically, cho ose k ripple = 30% to correspond to the peak - to - peak ripple current being 30% of the maximum output current. with this inductor value, the peak inductor current is i out (1 + k ripple /2). make sure that this peak inductor current is less than the controller ?s current limit. finally, select the inductor core size so that it does not saturate at the peak inductor current. input capacitor the input capacitor needs to be carefully selected to maintain sufficiently low ripple at the supply input of the conver ter. 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 100f. the best choice is the ceramic type, however, lo w 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 the shortest traces possible. in the case of tantalum or electrolytic types, they can be further away if a small parallel 0.1 f ceramic capacitor is placed right next to the ic. especially c8 capacitor should be placed as close as possible to the ic pin. output capacitor the output capacitor also needs to have low esr to keep low output voltage ripple. the output ripple voltage is:
rev 1.0 preliminary and all contents are subject to change without prior notice ? seaward electronics inc., 2 014 . ? www.seawardinc.com .cn ? page 7 se 2490 2.8a wide - input sensorless cc/cv step - down dc/dc converter where i outmax is the maximum output current, kripple is the ripple factor, r esr is the esr of the output capacitor, f lx is the switching frequency, l is the inductor value, and c out is the output capacitance. in the case of ceramic output capacito rs, 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 capacitors, the ripple is dominated by resr multiplied by the ripple current. in that c ase, the output capacitor is chosen to have sufficiently low esr. for ceramic output capacitor, typically choose a capacitance of about 470f. for tantalum or electrolytic capacitors, 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 a reverse voltage rating higher than the maximum input voltage. out put cable resistance compensation to compensate for resistive voltage drop across the charger's output cable, the SE2490 integrates a simple, user - programmable cable voltage drop compensation using the impedance at the fb pin. use the curve in figure 2 to choose the proper feedback resistance values for cable compensation. r fb1 is the high side resistor of voltage divider. figure2 cable compensation at various resistor divider values
rev 1.0 preliminary and all contents are subject to change without prior notice ? seaward electronics inc., 2 014 . ? www.seawardinc.com .cn ? page 8 se 2490 2.8a wide - input sensorless cc/cv step - down dc/dc converter typica l performance characteristics (continues)
rev 1.0 preliminary and all contents are subject to change without prior notice ? seaward electronics inc., 2 014 . ? www.seawardinc.com .cn ? page 9 se 2490 2.8a wide - input sensorless cc/cv step - down dc/dc converter typica l performance characteristics (continues) start up into cc mode v in =12v, v out =5v, i out =2.8a start up into cc mode v in =24v, v out =5v, i out =2.8a transient response (rising time) v in =12v, v out =5v, i out =0.01a~2.8a transient response (falling time ) v in =12v, v out =5v, i out =0.01a~2.8a transient response (rising time) v in =24v, v out =5v, i out =0.01a~2.8a transient response (falling time) v in =24v, v out =5v, i out =0.01a~2.8a
rev 1.0 preliminary and all contents are subject to change without prior notice ? seaward electronics inc., 2 014 . ? www.seawardinc.com .cn ? page 10 se 2490 2.8a wide - input sensorless cc/cv step - down dc/dc converter typica l performance characteristics (continues) short circuit v in =12v, v out =5v short circuit v in =24v, v out =5v output voltage ripple v in =12v, v out =5v, i out =2.8a output voltage ripple v in =24v, v out =5v, i out =2.8a
rev 1.0 preliminary and all contents are subject to change without prior notice ? seaward electronics inc., 2 014 . ? www.seawardinc.com .cn ? page 11 se 2490 2.8a wide - input sensorless cc/cv step - down dc/dc converter outlin e drawing for psop8 customer support seaward electronics incorporated ? china s ection b, 2nd floor, shangdi scientific office complex, #22 xinxi road haidian district, beijing 100085, china tel: 86 - 10- 8289 - 5700 /01/05 fax: 86 - 10- 8289 - 5706 seaward electronics corporation ? taiwan 2f, #181, sec. 3, min q uan east rd, taipei, taiwan r.o. c tel: 886 - 2 - 2712 - 0307 fax: 886 - 2 - 2712 - 0191 seaward electronics incorporated ? north america 1512 centre pointe dr. milpitas, ca95035, usa tel: 1 - 408- 821 - 6600

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