SE1051

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. 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 Application Adapters Digital Camera Chargers. Cellphone Chargers. Other Battery Chargers Ordering Information/Making Information Device Package SOT-23-6L (Lead-free) VOUT Fixed output voltages 1.21V Pin Configuration SE1051 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. Pin Description Name VCTRL GND VOUT ICTRL VSENSE VCC Pin# 1 2 3 4 5 6 Type Analog Input Power Supply Current Sink Output Analog Input Analog Input Power Supply Function Input Pin of the Voltage Control Loop Ground Line. 0V Reference For All Voltages Output Pin. Sinking Current Only Input Pin of the Current Control Loop Input Pin of the Current Control Loop Positive Power Supply Line 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 Absolute Maximum Rating Symbol VCC VIN θJA TJ TSTG TLEAD DC Supply Voltage Input Supply Voltage Thermal Resistance Junction to Ambient Operating Junction Temperature Range Storage Temperature Range Lead Temperature (Soldering 10 Sec) Parameter Maximum 18 -0.3~ VCC 250 0 to 125 -40 to 150 260 Units V V °C/W °C °C °C Electrical Characteristic VCC = 5.0V, TA = 25°C, unless otherwise specified. Symbol Parameter Test Condition Min Typ Max Unit Total Current Consumption ICC Total Supply Current - not taking the output sinking current into account Voltage Control Loop Gmv Transconduction Gain (VCTRL). Sink Current Only1) 0 < TA < 85°C VREF Voltage Control Loop Reference2) 0 < TA < 85°C IIBV Input Bias Current (VCTRL) 0 < TA < 85°C Current Control Loop Gmi VSENSE Transconduction Gain (ICTRL). Sink Current Only3) Current Control Loop Reference4) 0 < TA < 85°C IOUT = 2.5mA 0 < TA < 85°C IIBI Current out of pin ICTRL at -200mV 0 < TA < 85°C Output Stage VOL IOS Low output voltage at 10 mA sinking current Output Short Circuit Current. Output to VCC. Sink Current Only 0 < TA < 85°C 0 < TA < 85°C 300 22 35 mV mA 25 50 μA 2.9 240 mA/mV mV 50 100 nA 2.4 2.0 1.21 V mA/mV 0 < TA < 85°C 0.4 0.5 mA 1. If the voltage on VCTRL (the negative input of the amplifier) is higher than the positive amplifier input (VREF=1.210V), and it is increased by 1mV, the sinking current at the output OUT will be increased by 2.4mA. 2. The internal Voltage Reference is set at 1.210V. The internal Voltage Reference is fixed by bandgap, and trimmed to 0.5% accuracy at room temperature. 3. When the positive input at ICTRL is lower than -240mV, and the voltage is decreased 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 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 12/4/2008 Preliminary and all contents are subject to change without prior notice. © Seaward Electronics, Inc., 2006. • www.seawardinc.com.cn • Page 2 Block Diagram 1.21 0V Vcc Vout VCL Vctrl 240mV CCL GND Ictrl Typical Application Vsense Rs SE1051 1.210 V Cs 240mV CCL To prim ry a R2 Rout C2 22 pF Cic1 2.2nF Ric1 R1 Rvc1 Cvc1 2.2nF Vout+ Vcc VCL Vout Vctrl Lo ad GND Ictrl Vsense Rsen se Ric2 Vout- Fig.1 Typical Adapter or Battery Charger Application Using SE1051 In the above application schematic, the SE1051 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. VOUT = VREF × I LIMIT = Revision 12/4/2008 R1 + R 2 R1 VSENSE RSENSE Preliminary and all contents are subject to change without prior notice. © Seaward Electronics, Inc., 2006. • www.seawardinc.com.cn • Page 3 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 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. 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 100KΩ (or more) would be appropriate for the resistors R1 and R2. As an example, with R2 = 100KΩ, Vout = 4.10V, Vref = 1.210V, then R1 = 41.9KΩ. 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 = 240mΩ. Note that the Rsense resistor 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 amplifier, 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. 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 Fig.2 Output voltage 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 compensation network is shown in Fig.1. It consists of a capacitor Cvc1=2.2nF and a resistor Rcv1=470KΩ 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=22KΩ in series. When the Vcc voltage 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 330Ω in series with the opto-coupler in case Vcc=12V. 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-cost 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 18V, this low-cost auxiliary power supply can only be used in applications where the regulated line voltage does not exceed 9V. SE1051 1.210 V Rs Cs 240mV CCL To prim ry a R2 Rout C2 22 pF Cic1 2.2nF Rvc1 Cvc1 2.2nF Vout+ Vcc Vout VCL Vctrl GND Ictrl Vsense Ric1 R1 Rsen se Ric2 Vout- 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 5 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, 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 Last Updated - 12/4/2008 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