high precision cc/cv primary-side controller features 5% constant voltage regulation, 5%constant current regulation at universal ac input primary-side sensing and regulation without tl431 and opto-coupler low start-up current: 1 a (typical) low static current: 300 a (typical) programmable cv and cc regulation adjustable constant current and output power setting built-in secondary constant current control with primary side feedback peak-current-mode control compensates for transformer inductance tolerances compensates for cable voltage drop built-in leading edge blanking (leb) cycle-by-cycle current limiting vdd under-voltage lockout (uvlo) vdd over-voltage protection(ovp) applications ac/dc offline smps for cell phone charger digital cameras charger small power adapter auxiliary power for pc, tv etc. linear regulator/rcc replacement SI1128 is offered in sot23-6 package. typical applications pin order in schem is for demonstration not for real pin configuration the pin map is shown as below for sot23-6. pin order is oriented by marking SI1128 http://www.szsemi.com tel:0755-36858333 page: 1
general description the SI1128 is an excellent primary side feedback controller, which integrates several functions of protections. it minimizes the components counts and is available in a tiny sot-26 package. those make it an ideal design for low cost applications. SI1128 is especially designed for below 10w application such as mobile phone charger application etc. it provides functions of low startup current and leading-edge blanking of the current sensing. also, the SI1128 features ovp(over voltage protection) to prevent the circuit being damaged from the abnormal conditions. in most cases, the power supply with primary-side feedback controller would accompany with some serious load regulation effect. to deal with this problem, the SI1128 consists of dedicated load regulation compensation circuit to improve it. fig.1. typical cc/cv curve SI1128 http://www.szsemi.com tel:0755-36858333 page: 2
package dissipation rating package r ja ( /w) sot23-6 200 absolute maximum ratings (note) parameter value v dd voltage -0.3 to 30 base voltage -0.3 to 7v vc voltage -0.3 to 7v cs input voltage -0.3 to 7v fb input voltage -0.3 to 7v max operating junction temperature t 150 min/max storage temperature t stg -55 to 150 lead temperature (soldering, 10secs) 260 note: stresses beyond those listed under ?absolute maximum ratings? may cause permanent damage to the device. these are stress ratings only, functional operation of the device at these or any other conditions beyond those indicated recommended operating conditions? is not implied. exposure to absolute maximum-rated conditions for extended periods may affect device reliability. SI1128 http://www.szsemi.com tel:0755-36858333 page: 3
terminal assignments pin num pin name i/o description 1 gnd p ground 2 cs i the primary side current sense 3 base o base drive output to drive the external bjt 4 fb i inverting input to the error amplifier 5 vc i low pass filter capacitor for voltage compensation 6 vdd p supply voltage pin block diagram vdd 12.5v/6.8v uvlo comparator 27v ovp comparator internal supply 5v uvlo ovp vc cable drop compensation fb sampler sampling controller ea 2v cc controller switch controller ocp comparator ocp 500mv cs leading edge blanking base base driver gnd delay controller SI1128 http://www.szsemi.com tel:0755-36858333 page: 4
electrical characteristics (ta = 25 , vdd=15v, if not otherwise noted) symbol parameter test conditions min typ. max unit supply voltage (vdd) section i start-up start up current v dd =11v 1 3 ua i static static current v dd =15v 300 400 ua uvlo(on) v dd under voltage lockout enter v dd falling 6.0 6.8 7.6 v uvlo(off) v dd under voltage lockout exit v dd rising 11.5 12.5 13.5 v maximum v dd operation voltage 25 v ovp over voltage protection threshold 25 27 29 v current sense input section t leb leb time 500 ns v th_oc over current threshold 485 500 515 mv td_ oc ocp propagation delay 110 ns fb input section vref_fb reference voltage for feedback threshold 1.98 2.00 2.02 v tpause_min 2.0 us tpause_max maximum pause 8 10 12 ms icomp_cable maximum cable compensation current 42 45 48 ua base drive section is_max base sourcing maximum current 20 30 40 ma is_preoff base sourcing current after pre-off 0.5 1 1.5 ma rdson_i base drive low side on resistor 1 ohm SI1128 http://www.szsemi.com tel:0755-36858333 page: 5
application information operation overview this highly integrated psr controller contains several features to enhance the performance of low-power flyback converters. the patented topology of the psr controller allows for simplified of circuit designs, particularly battery charger applications. it operates in primary side sensing and regulation, thus opto-coupler and tl431 are not required. cv and cc control can be accurately achieved without secondary feedback circuitry. as a result, a low-cost, smaller, and lighter charger is produced when compared to a conventional design or a linear transformer. under voltage lockout (uvlo) an uvlo comparator is implemented to detect the voltage of vdd pin. it would assure the supply voltage enough to turn on the cl1128 controllers and further to drive the power bjt. a hysterics is built in to prevent the shutdown from the voltage dip during startup. the turn-on and turn-off threshold level are set at 12.5v and 6.8v, respectively. cc/cv operation SI1128 is designed to produce good cc/cv control characteristic as shown in the fig. 1. battery chargers are typically designed for two modes of operation, constant-voltage charging and constant-current charging. when the battery voltag e is low, the charger operates on a constant current charging. this is the main method for charging batteries and most of the charging energy is transferred into the batteries. when the battery voltage reaches its end-of-charge voltage, the current begins to taper-off. the charger then enters the constant voltage method of charging. finally, the charging current continues to taper-off until reaching zero. output voltage setting the SI1128 monitors the auxiliary fly-back signal from fb pin through a resistor divider pair of ra and rb. an error signal, which represents the difference between the voltage at fb and the reference voltage, is integrated with the error amplifier to control switching duty cycle. the output voltage is determined by the following relationship. for improving the output voltage accuracy, the transformer leakage inductance should be reduced as much as possible. 2(1 )( ) as out ba r n vv r n =+ where, r a and r b are the top and bottom feedback resistor value, n s and n a are the turn ratios of transformer secondary and auxiliary the load regulation and line regulation for primary side feedback control are sensitive to the structure of transformer. for getting good regulation and efficiency, the sandwich structure consisting of two secondary separate parallel layer windings surrounding primary winding is recommended. inductance correction circuitry if the primary magnetizing inductance is either too high or low the converter will automatically compensate for this by adjusting the oscillator frequency. since this controller is designed to operate in discontinuous-conduction mode the output power is directly proportional to the set primary inductance and its tolerance can be completely compensated with adjustments to the SI1128 http://www.szsemi.com tel:0755-36858333 page: 6
switching frequency. current sensing and leading edge blanking cycle-by-cycle current limiting is offered in SI1128. the switch current is detected by a sense resistor into the cs pin. when the power switch is turned on, a turn-on spike will occur on the sense-resistor. to avoid false-termination of the switching pulse, 500ns leading-edge blanking is built in. during this blanking period, the current sense comparator is disabled and the gate driver can not be switched off. base drive the external power bjt is driven by a dedicated base driver of SI1128. soft driver design elimination was used to minimize heat dissipati on, increase efficiency, and enhance reliability. programmable cable drop compensation in cv regulation control, the on-time of switch only regulates on-board voltage, not including output cable. different cable wire gauge or length results in different output voltage. the SI1128 has a cable compensation function used to compensate the output voltage drop due to output cable loss. an offset voltage is generated at fb by an internal current flowing into the resister divider. as the converter load increases from no-load to the peak power point (transition point between cv and cc) the voltage drop introduced across the output cable is compensated by increasing internal current flowing into the resister divider. the percentage of maximum compensation is ( ) 6 10 100% 2 comp a b out irr v v ? = v is load compensation voltage and out v is output voltage a r and b r is divide voltage resistance at fb pin protection control good power supply system reliability is achiev ed with its rich protection features including cycle-by-cycle current limiting (ocp), vdd clamp and under voltage lockout on vdd (uvlo). vdd is supplied by transformer auxiliary winding output. the output of SI1128 is shut down when vdd drops below uvlo (on) limit and the power converter enters power on start-up sequence thereafter. SI1128 http://www.szsemi.com tel:0755-36858333 page: 7
package mechanical data sot23-6 dimensions in mi llimeters dimensions in inches symbol min max min max a 1.000 1.300 0.039 0.051 a1 0.000 0.150 0.000 0.006 a2 1.000 1.200 0.039 0.047 b 0.300 0.500 0.012 0.020 c 0.100 0.200 0.004 0.008 d 2.800 3.020 0.110 0.119 e 1.500 1.700 0.059 0.067 e1 2.600 3.000 0.102 0.118 e 0.950 (bsc) 0.037 (bsc) e1 1.800 2.000 0.071 0.079 l 0.300 0.600 0.012 0.024 0o 8o 0o 8o SI1128 http://www.szsemi.com tel:0755-36858333 page: 8
SI1128 http://www.szsemi.com tel:0755-36858333 page: 9 z the information described herein is subject to change without notice. z is not responsible for any problems caused by circuits or diagrams described hereinwhose related industrial properties, patents, or other rights belong to third parties. the application circuit examples explain typical applications of the products, and do not guarantee the success of any specific mass-production design. z when the products described herein are regulated products subject to the wassenaar arrangement or other agreements, they may not be exported without authorization from the appropriate governmental authority. z use of the information described herein for other purposes and/or reproduction or copying without the express permission of is strictly prohibited. z the products described herein cannot be used as part of any device or equipment affecting the human body, such as exercise equipment, medical equipment, security systems, gas equipment, or any apparatus installed in airplanes and other vehicles, without prior written permission of z although exerts the greatest possible effort to ensure high quality and reliability, the failure or malfunction of semiconductor products may occur. the user of these products should therefore give thorough consideration to safety design, including redundancy, fire-prevention measures, and malfunction prevention, to prevent any accidents, fires, or community damage that may ensue. sany semiconductor sany semiconductor sany semiconductor sany semiconductor
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