revision 12/4/2008 preliminary and all contents are subject to change without prior notice. ? seaward electronics, inc., 2006. ? www.seawardinc.com.cn ? page 1 features ? constant voltage and constant current control ? low voltage operation at 3v ? precision internal voltage reference ? low external component count ? current sink output stage ? easy compensation ? low ac mains voltage rejection ? rugged 2kv esd withstand capability. ? available in sot-23-6l package. ? 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) modes. SE1051 integrates one voltage reference, two operational amplifiers (the outputs are or?ed together, common collectors), and a current sensing circuit. the voltage reference, together with one operational amplifier, makes it an ideal voltage controller. the other low voltage reference, together with another operational amplifier, makes it an ideal current limiter for low side output current sensing. the current threshold is fixed, and precise. the SE1051, housed 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 configuration application ? adapters ? digital camera chargers. ? cellphone chargers. ? other battery chargers ordering information/making information device package v out SE1051 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 voltage 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 loop 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 for lead-free process.
revision 12/4/2008 preliminary and all contents are subject to change without prior notice. ? seaward electronics, inc., 2006. ? www.seawardinc.com.cn ? page 2 absolute maximum rating symbol parameter maximum units v cc dc supply voltage 18 v v in input supply voltage -0.3~ v cc v ja thermal 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 = 5.0v, t a = 25c, unless otherwise specified. symbol parameter test condition min typ max unit total current consumption 0.4 i cc total supply current - not taking the output sinking current into account 0 < t a < 85c 0.5 ma voltage control loop 2.4 gmv transconduction gain (v ctrl ). sink current only 1) 0 < t a < 85c 2.0 ma/mv 1.21 v ref voltage control loop reference 2) 0 < t a < 85c v 50 i ibv input bias current (v ctrl ) 0 < t a < 85c 100 na current control loop gmi transconduction gain (i ctrl ). sink current only 3) 0 < t a < 85c 2.9 ma/mv i out = 2.5ma 240 v sense current control loop reference 4) 0 < t a < 85c mv 25 i ibi current out of pin i ctrl at -200mv 0 < t a < 85c 50 a output stage v ol low output voltage at 10 ma sinking current 0 < t a < 85c 300 mv 22 i os output short circuit current. output to v cc . sink current only 0 < t a < 85c 35 ma 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 1m v, the sinking current at the out put out will be increased by 2.4ma. 2. the internal voltage reference is set at 1.210v. t he internal voltage reference is fixed by bandgap, and trimmed to 0.5% accuracy at room temperature. 3. when the positive input at i ctrl is lower than -240mv, and the voltage is de creased by 1mv, the sinking current at the output out will be increased by 2.9ma. 4. the internal current sense threshold is set to -240mv. the current control loop prec ision takes into account the cumulative effects of the internal voltage reference deviation as well as the input offs et voltage of the trans - conduction operational amplifier.
revision 12/4/2008 preliminary and all contents are subject to change without prior notice. ? seaward electronics, inc., 2006. ? www.seawardinc.com.cn ? page 3 block diagram typical application rsense r2 r1 ric2 ric1 cic1 c2 rvc1 cvc1 2.2nf 22pf 2.2nf v out + v out - to pri mar y rout ictrl vsense gn d vct rl vout vcc 240mv se10 51 load 1.210v vcl ccl cs rs fig.1 typical adapter or battery charger application using SE1051 in the above application schematic, the SE1051 is used on t he secondary side of a flyback adapter (or battery charger) to provide an accurate control of vo ltage 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 1.210v 240mv vcc vout vctrl gnd vsense ictrl vcl ccl
revision 12/4/2008 preliminary and all contents are subject to change without prior notice. ? seaward electronics, inc., 2006. ? www.seawardinc.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 highly 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 current loop is controlled via the second trans-conductance operational amplifier, the sense resistor rsense, and the optocoupler. the control equation is: rsense x i-limit = vsense eq2 rsense = vsense / i-limit eq3 where i-limit is the desired current limit, and vsense is the threshold voltage for the current control loop. as an example, with i-limit = 1a, vsense = -240mv, then rsense = 240m . note that the rsense resi stor should be selected with the consideration of the maximum power in full load operations (p-limit). p-limit = vsense x i-limit. eq4 as an example, with i-limit = 1a, and vsense =-240mv, p-limit = 240mw. consequently, for most adapter and battery charger applications, a quarter-watt resistor to make the current sensing function is sufficient. 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 am plifier, and its foot is to be connected to lower potential point 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 voltage versus output current compensation the voltage-control trans-conductance operational amplifier can be fully compensated. both of its output and negat ive 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 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 voltage reaches 12v it could be interesting to limit the current coming through the output in the aim to reduc e 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 12/4/2008 preliminary and all contents are subject to change without prior notice. ? seaward electronics, inc., 2006. ? www.seawardinc.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 ensu red 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 lo w-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-cost power supply can reach voltages as high as twice the voltage of the r egulated line. since the absolute maximum rating of the SE1051 supply voltage is 18v, this low-cost auxiliary power supply can only be used in applications where the regulated line voltage does not exceed 9v. rsense r2 r1 ric2 ric1 cic1 c2 rvc1 cvc1 2.2nf 22pf 2.2nf v out + v out- to pri mar y rout rs ictrl vsense gn d vct rl vout vcc 240mv SE1051 cs 1.210v vcl ccl fig. 3
revision 12/4/2008 preliminary and all contents are subject to change without prior notice. ? seaward electronics, inc., 2006. ? www.seawardinc.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, minquan east rd, ta i p e i , ta i w a n 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 last updated - 12/4/2008
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