revision 11/24/2015 preliminary and all contents are subject to change without prior notice. ? seaward electronics, inc., 200 6 . ? www.sea wardinc.com .cn ? page 1 features ? c onstant voltage and constant current control ? l ow voltage operation at 3v ? p recision inter nal voltage reference ? l ow external component count ? c urrent s ink o utput s tage ? e asy c ompensation ? l ow ac m ains v oltage r ejection ? rugged 2 kv esd withstand ca pability. ? available in sot - 2 3 - 6l p ackage. ? rohs compliant and 100% lead (pb) - free description se1051 is a highly integrated solution for smps applications requiring cv (constant voltage) and cc (constant current) mode s . se1051 integrates one voltage reference, two operational amplifiers ( the outputs are or ?ed together, common collectors), and a current sens ing circuit. the voltage reference, together with one operational amplifier , makes it an ideal voltage controller. t he other low voltage reference , together with another operational amplifier , makes it an i deal current limiter for low side output current sensing. the current threshold is fixed, and precise. the se1051 , house d in space - saving sot23 - 6l package, is ideal for space sensitive applications such as adapters, cellphone chargers, digital camera chargers, and other battery chargers. pin configurat ion application ? a dapters ? digital camera chargers. ? cellphone chargers. ? other b attery chargers ordering information /making infor m ation device package v out se 1051 sot - 23- 6l (lead - free) fixed output voltages 1.21v pin description name pin# type function v ctrl 1 analog input input pin of the voltag e control loop gnd 2 power supply ground line. 0v reference for all voltages v out 3 current sink output output pin. sinking current only i ctrl 4 analog input input pin of the current control loop v sense 5 analog input input pin of the current control l oop v cc 6 power supply positive power supply line package making information pin1 is down in the left - hand corner. the last character is the batch number.a dot on top right corner is f or lead - free process.
revision 11/24/2015 preliminary and all contents are subject to change without prior notice. ? seaward electronics, inc., 200 6 . ? www.sea wardinc.com .cn ? page 2 absolute maximum rating symbol parameter maximum units v cc dc supply voltage 1 4 v v in input supply voltage - 0.3~ v cc v ja t hermal resistance junction to ambient 250 c /w t j operating junction temperature range 0 to 125 c t stg storage temperature range - 40 to 150 c t lead lead temperature (soldering 10 sec ) 260 c electrical characteristic v cc = 5.0 v , t a = 25c , unless otherwise specified. symbol parameter test condition min typ max unit total current consumption i cc total supply current - not taking the output sinking current into account 0.4 ma 0 < t a < 85c 0.5 voltage control loop gmv transconduction g ain (v ctrl ). sink current only 1) 1.0 ma/mv 0 < t a < 85c 2.0 v ref voltage control loop reference 2) 1.186 1.21 1.234 v 0 < t a < 85c i ibv input bias current ( v ctrl ) 50 na 0 < t a < 85c 100 current control loop gmi transcond uction gain ( i ctrl ). sink current only 3) 0 < t a < 85c 2.5 ma/mv v sense current control loop reference 4) i out = 2.5ma 200 mv 0 < t a < 85c i ibi current out of pin i ctrl at - 200mv 25 a 0 < t a < 85c 50 output stage v ol low output voltage at 10 ma sinking current 0 < t a < 85c 350 mv i os output short circuit current. output to v cc . sink current only 22 ma 0 < t a < 85c 35 1. if the voltage on v ctrl (the negative input of the amplifier) is higher than the positive amplifier input (v ref =1.210v), and it is increased by 1mv, the sinking current at the output out will be increased by 1.0 ma. 2. the internal voltage reference is set at 1.210v. the internal voltage refere nce is fixed by bandgap, and trimmed to 0.5% accuracy at room temperature. 3. when the positive input at i ctrl is lower than - 200mv , and the voltage is decreased by 1mv, the sinking current at the output out will be increased by 2.5 ma. 4. the internal curr e nt sense threshold is set to - 200mv . th e current control loop precision takes into account the cumulative effects of the internal voltage reference deviation as well as the input offset voltage of the trans - conduction operational amplifier.
revision 11/24/2015 preliminary and all contents are subject to change without prior notice. ? seaward electronics, inc., 200 6 . ? www.sea wardinc.com .cn ? page 3 block diagram typical ap plication fig.1 typical adapter or battery charger application using se 1051 in the abov e application schematic, the se 1051 is used on the secondary side of a flyback adapter (or battery charger) to provide an accurate control of voltage and current. the above feedback loop is made with an optocoupler. sense sense limit ref out r v i r r r v v = + = 1 2 1
revision 11/24/2015 preliminary and all contents are subject to change without prior notice. ? seaward electronics, inc., 200 6 . ? www.sea wardinc.com .cn ? page 4 application hints voltage control the voltage loop is controlled via a first transconductance operational amplifier, the resistor bridge r1, r2, and the optocoupler which is directly connected to the output. the relation between the values of r1 and r2 should be chosen as written in equation 1. r1 = r2 x vref / (vout - vref) eq1 where vout is the desired output voltage. to avoid the discharge of the load, the resistor bridge r1, r2 should be highl y resistive. for this type of application, a total value of 100k ? (or more) would be appropriate for the resistors r1 and r2. as an example, with r2 = 100k ? , vout = 4.10v, vref = 1.210v, then r1 = 41.9k ? . note that if the low drop diode should be inserted between the load and the voltage regulation resistor bridge to avoid current flowing from the load through the resistor bridge, this drop should be taken into account in the above calculations by replacing vout by (vout + vdrop). current control the curre nt loop is controlled via the second trans - conductance operational amplifier, the sense resistor rsense, and the optocoupler. the control equation is : r sense x i lim it = v sense eq 2 r sense = v sense / i limit eq 3 where i - lim it is the desired current limit , and vsense is the threshold voltage for the current control loop. as an example, with i - lim it = 1a , vsense = - 200mv , then rsense = 2 0 0m ? . note that the rsense resistor should be selected with the consideration of the maximum power in full load oper ations (p - limit) . p - limit = vsense x i - limit . eq 4 as an example, with i - limit = 1a, and vsense = - 200mv , p - limit = 2 0 0mw. consequently , for most adapter and battery charger applications, a quarter - watt resistor to make the current sensing function is suffi cient. vsense threshold is achieved internally by a resistor bridge tied to the vref voltage reference. its middle point is tied to the positive input of the current control operational amplifier, and its foot is to be connected to lower potential po int of the sense resistor as shown on the following figure. the resistors of this bridge are matched in layout to provide the best precision possible. the current sinking outputs of the two trans - conductance operational amplifiers are connected together . this makes an oring function which ensures that whenever the current or the voltage reaches too high values, the optocoupler is activated. the relation between the controlled current and the controlled output voltage can be described with a square characteristic as shown in the following v/i output - power graph. fig.2 output vol tage versus output current compensation the voltage - control trans - conductance operational amplifier can be fully compensated. both of its output and negative input are directly accessible for external compensation components. an example of a suitable comp ensation network is shown in fig. 1 . it consists of a capacitor cvc1=2.2nf and a resistor rcv1=470k ? in series, connected in parallel with another capacitor cvc2=22pf. the current - control trans - conductance operational amplifier can also be fully compensated . both of its output and negative input are directly accessible for external compensation components. an example of a suitable compensation network is shown in fig. 1 . it consists of a capacitor cic1=2.2nf and a resistor ric1=22k ? in series. when the vcc vo ltage reaches 12v it could be interesting to limit the current coming through the output in the aim to reduce the dissipation of the device and increase the stability performances of the whole application. an example of a suitable rout value could be 330? in series with the opto- coupler in case vcc=12v.
revision 11/24/2015 preliminary and all contents are subject to change without prior notice. ? seaward electronics, inc., 200 6 . ? www.sea wardinc.com .cn ? page 5 start up and short circuit conditions under start - up or short - circuit conditions the se1051 does not have a high enough supply voltage. this is due to the fact that the chip has its power supply line in common with the power supply line of the charger system. consequently , the current limitation can only be ensured by the primary pwm module, which should be designed accordingly. if the primary current limitation is considered not to be precise enough for the application, then a sufficient supply for the se1051 has to be ensured under any condition. it would then be necessary to add some circuitry to supply the chip with a separate power line. this can be achieved in numerous ways, including an additional winding on the transformer. the following schematic shows how to realize a low - cost power supply for the se1051 (with no additional windings). please pay attention to the fact that in the particular case presented here, this low - co st power supply can reach voltages as high as twice the voltage of the regulated line. since the absolute maximum rating of the se1051 supply voltage is 18 v, this low - cost auxiliary power supply can only be used in applications where the regulated line vol tage does not exceed 9 v. fig. 3
revision 11/24/2015 preliminary and all contents are subject to change without prior notice. ? seaward electronics, inc., 200 6 . ? www.sea wardinc.com .cn ? page 6 outline drawing sot - 23- 6l customer support seaward electronics incorporated ? china section 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 - 2 712 - 0307 fax: 886 - 2 - 2712 - 0191 seaward electronics incorporated ? north america 1512 centre pointe dr. milpitas, ca95035, usa tel: 1 - 408- 821 - 6600 last updated - 11/24/2015
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