rev. 2 jan.2012 WS2268 t21-2 copyright@winsemi mircroelectronics.,ltd.,all rights reserved. primary side ac/dc controller features lower no-load power lower start-up current built-in cable compensation built-in peak current compensation random frequency modulation to reduce system emi built-in leading edge blanking current limited protection in each cycle over voltage protection open circuit protection under voltage lockout application adapters/chargers for cell/cordless phones, pdas, mp3 and other portable apparatus standby and auxiliary power supplies gerneral description the WS2268 is a high performance ac/dc power supply controller for battery charger and adapter applications. the device uses pulse frequency modulation (pfm) method to build discontinuous conduction mode (dcm) flyback power supplies. the WS2268 provides accurate constant voltage, constant current (cv/cc) regulation without requiring the opto-coupler and the secondary control circuitry. it also eliminates the need of loop compensation circuitry while maintaining stability. the WS2268 achieves excellent regulation and high power efficiency, the no-load power consumption is less than 100mw. the WS2268 is available in sop8 package. typical application WS2268
2 / 8 WS2268 steady, keep for your advance genenral information pin configuration marking information termianl assignments block diagram pin number pin name function 1 ip the primary current sense 2 vp supply voltage 3 g this pin drives the base of external power npn switch 4 gnd ground 5 pcc this pin connects a resistor for peak current compensation 6 u the voltage feedback from the auxiliary winding 7 cdc this pin connects a resistor for cable compensation 8-null line1 w :winsemi logo line2 device name(WS2268sp) line 3 lot code y: year code(0:2010,1:2011 ) ww: week code(1-52) constant voltage control constant current control WS2268sp dvf yww
3 / 8 WS2268 steady, keep for your advance recommended condition parameter value unit supply voltage vp 10~30 v operating temperature -20~85 absolute maximum ratings(note 1) parameter value unit supply voltage vp 30 v feedback voltage u -40~10 v others ip, g, pcc, cdc -0.3~7 v output current at g internally limited a power dissipation at ta=25 0.657 w operating junction temperature 150 storage temperature -65~150 thermal resistance junction-to-ambient 190 /w note 1 stresses greater than those listed under ?absolute maximum rating? may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under ?recommended operating conditions? is not implied. exposure to ?absolute maximum rating? for extended periods may affect device reliability. electrical characteristics (tc = 25c) parameter symbol conditions min typ max unit start-up section start-up threshold vstu 18 20 22 v uvlo threshold vlo 7 9 11 v start-up current istart vp=vstu-0.5v 3 5 ua operating current i is static 600 900 ua current sense section ip compare threshold vip 475 500 525 mv leading edge blanking t leb 500 ns feedback section feedback threshold voltage vs&href 4 v input resistor ru dynamic 350 k ? over voltage protection vovp 7 8 9 v open circuit protection vlotage vockp -1.2 -1 -0.8 v drive output section output low voltage vol io = -20ma 0.8 v output high voltage voh io = 20ma 8 v output clamp vclamp 19 v rise time tr cl = 1nf 200 ns fall time tf cl = 1nf 70 ns
4 / 8 WS2268 steady, keep for your advance esd information symbol parameter value unit v esd_hbm human model 2000 v v esd_mm machine model 400 v ordering information package ic marking information purchasing device name 8 pin sop8, pb-free WS2268sp WS2268
5 / 8 WS2268 steady, keep for your advance typical operating characteristics vstart vs temp 19.95 20 20.05 20.1 20.15 20.2 20.25 20.3 20.35 20.4 20.45 -40 0 40 80 120 160 temp() vstart ( v ) vstop vs temp 8.3 8.4 8.5 8.6 8.7 8.8 8.9 9 -40 0 40 80 120 160 temp() vsto p( v ) ist vs temp 0 0.5 1 1.5 2 2.5 -40 0 40 80 120 160 temp() ist(ua) iop vs temp 0 100 200 300 400 500 600 700 800 900 -40 0 40 80 120 160 temp() io p (ua)
6 / 8 WS2268 steady, keep for your advance operration description 1. startup mode at the phase of power-on, the rectified high voltage dc charges the capacitor of vp through the start-up resistor. when vp rises to 20v, the ic enters normal operation, then switching begins and the output voltage begins to rise. the vp bypass capacitor must supply the ic until the output voltage builds up enough to provide power from the auxiliary winding to sustain the vp. the under-voltage threshold of vp is 9v, and therefore, the voltage on the vp capacitor must not drop more than 11v while the output is charging up. 2. constant primary peak current the primary current ip(t) is sensed by a current sense resistor rcs, the current rises up linearly at a rate of: lm t vg dt t dip ) ( ) ( = 1 primary current waveform as illustrated in top figure when the current ip(t) rises up to ipk, the switch turns off. the constant peak current is given by: rcs vcs ipk = 2 .the energy stored in the magnetizing inductance lm each cycle is : 2 2 1 ipk lm eg = 3 so the power transferring from the input to the output is given by: sw f ipk lm p = 2 2 1 4 where sw f is the switching frequency. when the peak current ipk is constant, the output power depends on the switching frequency sw f . 3. constant voltage operation the WS2268 captures the auxiliary winding feedback voltage at u pin and operates in constant-voltage (cv) mode to regulate the output voltage. assuming the secondary winding i s master, the auxiliary winding is slave during the d1 on-tim e the auxiliary voltage is given by: ns vs nau x vaux = vd vo vs + = so, ) ( vd vo ns naux vaux + ? = ) 3 2 1 ( * r r vu vaux + = where vd is the diode forward drop voltage. auxiliary voltage waveform the output voltage is different from the secondary voltage in a diode forward drop voltage that depends on the current. if the secondary voltage is always detected at a fixed secondary current, the difference between the output voltage and the secondary voltage will be a fixed vd. the voltage detection point is at two-thirds of the d1 on-time. the cv loop control function of WS2268 then generates a d1 off-time to regulate the output voltage. 4 constant current operation secondary current waveform in cc operation, the cc loop control function of WS2268 will keep a fixed proportion between d1 on-time tons and d1 off-time toffs by discharging or charging the capacitance. the fixed proportion is:
7 / 8 WS2268 steady, keep for your advance 3 4 = toffs tons the relationship between the output constant-current iout and secondary peak current ipks is given by: toffs tons tons ipks iout + = 2 1 at the instant of d1 turn-on, the primary current transfers to the secondary at an amplitude of: ipk ns np ipks = thus the output constant-current is given by: ipk ns np toffs tons tons ipk ns np iout = + = 7 2 2 1 5. leading edge blanking 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, a 430ns 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. 6. ccm protection the WS2268 is designed to operate in discontinuous conduction mode (dcm) in both cv and cc modes. to avoid operating in continuous conduction mode (ccm), the WS2268 detects the falling edge of the u input voltage on each cycle. if a 0.1v falling edge of u is not detected, the WS2268 will stop switching. 7. ovp & ockp WS2268 include output over-voltage protection (ovp) and open circuit protection (ockp) circuitry. if the voltage at u pin exceeds 8v, 100% above the normal detection voltage, or the -1v falling edge of u input can not be monitored, the WS2268 will immediately shut off and enter hiccup mode. the WS2268 sends out a fault detection pulse every 19ms in hiccup mode until the fault has been removed.
8 / 8 WS2268 steady, keep for your advance sop8 package information unit:mm(inch)
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