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?on-bright electronics confidential - 1 - ob_doc_ds_8800 OB2288 highly integrated current mode pwm controller general description OB2288 is a highly integrated current mode pwm controller. with internal maximum 50% duty cycle limit, it is very suitable to be used in large power applications, especially in forward topology. OB2288 offers comprehensive protection coverage including cycle-by-cycle current limiting, internal power-on soft start, vdd under voltage lockout (uvlo), vdd over voltage protection(ovp), vdd clamp, gate clamp, over load protection(olp), over temperature protection (otp), brownout protection (bop). OB2288 also features protections against pin open and short conditions on selected pins. moreover, an internal 1-second restart timer prevents permanent olp latch when the supply of the controller is provided by other dc sources. in general applications where supply is self biased by auxiliary winding, this restart timer will never be triggered. in OB2288, on-bright proprietary frequency shuffling technique together with soft switching control at the totem pole gate drive output help to lower the system design barrier to achieve good emi performance. to meet the increasing stringent standby power requirements at light or no load condition, on-bright proprietary ?extended burst mode? technology eases the system design with high performance and without compromise in audio noise. OB2288 is offered in sop-8 and dip-8 packages. features maximum 50% duty cycle limit ac line brownout detection & protection (bop) latch-off mode fault protection internal restart timer all pins floating protection and ri short protection proprietary extended burst mode control for improved efficiency and minimum standby power design audio noise free operation external programmable pwm switching frequency built-in frequency shuffling for better emi internal leading edge blanking high precision reference voltage for otp and brownout protection power-on soft start internal synchronized slope compensation 1a peak current drive capability applications offline ac/dc converter for lcd tv/pc power supplies open-frame smps typical application on-bright confidential to bona free datasheet http://www.datasheetlist.com/
?on-bright electronics confidential - 2 - ob_doc_ds_8800 OB2288 highly integrated current mode pwm controller general information pin configuration the pin map of OB2288 in dip8 and sop8 package is shown as below. 1 2 3 4 8 7 6 5 gnd fb bo ri gate vdd sense rt ordering information part number description OB2288ap dip8, pb-free in tube OB2288cp sop8, pb-free in tube OB2288cpa sop8,pb-free in taping package dissipation rating package r ja ( c/w) dip8 90 sop8 150 absolute maximum ratings parameter value vdd zener clamp voltage (v clamp ) 31 v vdd zener clamp continuous current 10 ma bo input voltage -0.3 to 7v fb input voltage -0.3 to 7v sense input voltage -0.3 to 7v rt input voltage -0.3 to 7v ri input voltage -0.3 to 7v min/max operating junction temperature t j -20 to 150 o c min/max storage temperature t stg -55 to 150 o c lead temperature (soldering, 10secs) 260 o c note: stresses beyond those listed under ?absolute maximum ratings? may cause permanent damage to the device. these are stress ratings only, functional operat ion of the device at these or any other conditions beyond thos e indicated under ?recommended operating conditions? is not im plied. exposure to absolute maximum-rated conditions for ex tended periods may affect device reliability. OB2288 x x x highly integrated current mode pwm controller package a:dip8 c:sop8 packing blank : tube a : taping package pb-free p : lead free on-bright confidential to bona free datasheet http://www.datasheetlist.com/
?on-bright electronics confidential - 3 - ob_doc_ds_8800 OB2288 highly integrated current mode pwm controller marking information terminal assignments pin num pin name i/o description 1 gnd p ground. 2 fb i feedback input pin. pwm duty cycle is determined by voltage level at this pin and current-sense signal level at pin 6. 3 bo i/o brownout detection pin. detects lin e voltage through a resistor divider. if the voltage at this pin drops below 1.05v and lasts 50ms, brownout is triggered and pwm output will be disabled. 4 ri i internal oscillator frequency setting pin. a resistor connected between ri and gnd sets the pwm frequency. 5 rt i dual function pin. either connected through a ntc resistor to gnd for over temperature shutdown control or used as latch shutdown control input. 6 sense i current sense input pin. connected to mosfet current sensing resistor node. 7 vdd p dc power supply pin. 8 gate o totem-pole gate drive output for power mosfet. on-bright confidential to bona free datasheet http://www.datasheetlist.com/
?on-bright electronics confidential - 4 - ob_doc_ds_8800 OB2288 highly integrated current mode pwm controller block diagram recommended oper ating condition symbol parameter min max unit vdd vdd supply voltage 11.5 25 v ri ri resistor value 10 40 kohm t a operating ambient temperature -20 85 o c on-bright confidential to bona free datasheet http://www.datasheetlist.com/
?on-bright electronics confidential - 5 - ob_doc_ds_8800 OB2288 highly integrated current mode pwm controller electrical characteristics (t a = 25 o c, ri=20k ohm, vdd=16v, if not otherwise noted) symbol parameter test conditions min typ max unit supply voltage (vdd) section i_vdd_startup vdd startup current vdd =13.5v 5 20 ua i_vdd_ops operation current v fb =3v 2.3 ma uvlo(enter) vdd under voltage lockout enter 8 9 10 v uvlo(exit) vdd under voltage lockout exit 14.2 15.2 16.2 v ovp vdd over voltage protection 26 28 30 v t d _ovp vdd ovp debounce time 100 usec vdd_de-latch latch release voltage threshold 6.5 v i_vdd_latch vdd current at latch shutdown vdd=8v 45 ua v dd _clamp v dd zener clamp voltage i(v dd ) = 15 ma 31 v t_softstart soft start time 4 msec feedback input section(fb pin) a vcs pwm input gain v fb / v cs 2.2 v/v v fb_ open fb pin open voltage vdd=18v 6 v i fb _max fb pin maximum source current vdd=18v, short fb pin to gnd. 1.1 ma v fb _ th zero duty cycle threshold voltage vdd=9.5v, vsense=0v 0.9 1 1.1 v v th _bm burst mode fb threshold voltage 1.6 v v th _pl power limiting fb threshold voltage 4.4 v t d _pl power limiting debounce time 250 msec z fb _in input impedance 6 kohm current sense input(sense pin) section t_blanking sense input leading edge blanking time vdd=18v 300 nsec v th _oc internal current limiting comparator threshold 0.67 0.7 0.73 v t d _oc propagation delay to gate cl=1nf at gate 70 nsec oscillator section f osc normal oscillation frequency 60 65 70 khz ? f(shuffle)/fosc frequency shuffling range -4 4 % f_shuffle frequency shuffling cycling frequency 32 hz ? f_temp frequency temperature stability -20 o c to 100 o c 3 % on-bright confidential to bona free datasheet http://www.datasheetlist.com/
?on-bright electronics confidential - 6 - ob_doc_ds_8800 OB2288 highly integrated current mode pwm controller ? f_vdd frequency voltage stability vdd = 12-25v 3 % dmax max duty cycle 45 48 50 % dmin min duty cycle - - 0 % ri_range operating ri range 10 20 40 kohm v_ri ri operation voltage 2.0 v f_bm burst mode pulse switching frequency 22 khz gate drive output vol low output voltage io = 30 ma (sink) 0.3 v voh high output voltage io = 30 ma (source) 11 v vg_clamp output clamp voltage vdd=25v 17 v t_r rising time cl = 1nf, 10-90%. 70 nsec t_f falling time cl = 1nf, 10-90%. 30 nsec over temperature protection i_rt rt pin source current vdd = 18v 100 ua v th _otp otp threshold voltage vdd = 18v 1.0 1.05 1.1 v v th _otp_off otp recovery threshold voltage vdd = 18v 1.15 v v th _rt_latch rt input latch threshold voltage vdd = 18v 0.6 v t d _otp otp de-bounce time vdd = 18v 100 usec v_rt_open rt pin floating voltage vdd = 18v 3.2 v brownout section vth_bo brownout threshold 1.0 1.05 1.1 v t d _bo brownout debounce time 50 msec ibo_hys source current for brownout hysteresis programming 2 ua restart timer section rst_auto auto recovery restart timer 1 sec on-bright confidential to bona free datasheet http://www.datasheetlist.com/
?on-bright electronics confidential - 7 - ob_doc_ds_8800 OB2288 highly integrated current mode pwm controller characterization plot i_vdd vs load 1 2 3 4 5 6 0 500 1000 1500 2000 load(nf) i_vdd(ma) 50khz 65khz 100khz i_rt vs ri 0 50 100 150 200 250 10 20 30 40 50 ri(kohm) i_rt(ua) fosc vs ri 0 30 60 90 120 150 10 20 30 40 50 ri(kohm) fosc(khz) fosc vs vdd 50 55 60 65 70 75 10 13 16 19 22 25 vdd(v) fosc(khz) i_vdd_startup vs temperature 1.0 1.2 1.4 1.6 1.8 2.0 -20 10 40 70 100 130 temperature( ) i_vdd_startup(ua ) v fb_ open vs temperature 5.90 5.95 6.00 6.05 6.10 -20 10 40 70 100 130 temperature( ) v fb_ open(v) on-bright confidential to bona free datasheet http://www.datasheetlist.com/
?on-bright electronics confidential - 8 - ob_doc_ds_8800 OB2288 highly integrated current mode pwm controller i_vdd_lacth vs temperature 35 40 45 50 55 60 -20 10 40 70 100 130 temperature( ) i_vdd_lacth(ua) fosc vs temperature 60 61 62 63 64 65 66 -20 5 30 55 80 105 130 temperature( ) fosc(khz) uvlo(enter) vs temperature 8.0 8.5 9.0 9.5 10.0 -20 10 40 70 100 130 temperature( ) uvlo(enter)(v) uvlo(exit) vs temperature 15.0 15.1 15.2 15.3 15.4 15.5 -20 10 40 70 100 130 temperature( ) uvlo(exit)(v) on-bright confidential to bona free datasheet http://www.datasheetlist.com/
?on-bright electronics confidential - 9 - ob_doc_ds_8800 OB2288 highly integrated current mode pwm controller operation description OB2288 is a highly integrated pwm controller ic optimized for forward mode converter applications. the versatile protections and high performance make it very suitable for large power applications. z startup current and startup control startup current of OB2288 is designed to be very low so that vdd could be charged up above uvlo(exit) threshold level and device starts up quickly. a large value startup resistor can therefore be used to minimize the power loss yet reliable startup in application. for a typical ac/dc adaptor with universal input range design, a 2 m ? , 1/8 w startup resistor could be used together with a vdd capacitor to provide a fast startup and yet low power dissipation design solution. z operating current the operating current of OB2288 is low at 2.3ma. good efficiency is achieved with OB2288 low operating current together with extended burst mode control schemes at zero or light load condition. z extended burst mode operation at zero load or light load condition, most of the power dissipation in a switching mode power supply is from switching loss on the mosfet transistor, the core loss of the transformer and the loss on the snubber circuit. the magnitude of power loss is proportional to the number of switching events within a fixed period of time. reducing switching events leads to the reduction on the power loss and thus conserves the energy. OB2288 self adjusts the switching mode according to the loading condition. at no load or light load conditions, the fb input drops below burst mode threshold level. device enters burst mode control. the gate drive output switches only when vdd voltage drops below a preset level and fb input is active to output an on state. otherwise the gate drive remains at off state to minimize the switching loss thus reduce the standby power consumption to the greatest extend. the nature of high frequency switching also reduces the audio noise at any loading conditions. z oscillator/frequency shuffling operation a resistor connected between ri and gnd sets the constant current source to charge/discharge the internal cap and thus the pwm oscillator frequency is determined. the relationship between ri and switching frequency follows the below equation within the specified ri in kohm range at nominal loading operational condition. ) ( ) ( 1300 khz kohm ri f osc in OB2288, the proprietary frequency shuffling method can soften the emi signature by spreading the energy in the vicinity of the main switching component and its harmonics. the magnitude of shuffling lies in the range of 4% of the main switching frequency. z current sensing and leading edge blanking cycle-by-cycle current limiting is offered in OB2288 current mode pwm control. the switch current is detected by a sense resistor into the sense pin. an internal leading edge blanking circuit chops off the sense voltage spike at initial mosfet on state due to snubber diode reverse recovery so that the external rc filtering on sense input is no longer needed. the current limit comparator is disabled and can not turn off the external mosfet during the blanking period. the pwm duty cycle is determined by the current sense input voltage and the fb input voltage. z over temperature protection with latch shutdown a ntc resistor in series with a regular resistor should be connected between rt and gnd for temperature sensing and protection. ntc resistor value becomes lower when the ambient temperature rises. with a fixed internal current i rt flowing through the resistors, the voltage at rt pin becomes lower at high temperature. the internal otp circuit is triggered and shuts down the mosfet when the sensed input voltage is lower than v th _otp. it is selectable for auto recover or latched shutdown. z rt pin used as latch shutdown input control rt pin could also be used as a control input to implement system latch shutdown function. an example is to implement system ovp protection with a latch shutdown function through a photo coupler and affiliated circuits. when ovp detection signal connected to rt is lower than v th _otp OB2288 controls system into latch shutdown. the recovery of the ac/dc system could only be realized by resetting internal latch when vdd voltage drops below vdd_de-latch on-bright confidential to bona free datasheet http://www.datasheetlist.com/
?on-bright electronics confidential - 10 - ob_doc_ds_8800 OB2288 highly integrated current mode pwm controller value. this could be achieved by unplugging/re- plugging of ac source in ac start-up configuration. z brownout protection by monitoring the voltage level on pin bo during normal operation, the controller protects the smps against low main condition. when bo voltage level falls below 1.05v, and if it lasts for about 50ms, the controller stops pulsing until this level goes back and the operation resumes. by adjusting the resistor divider connected between the high input voltage and this pin, start and stop levels are programmable. z restart timer in some special applications, such as lcdtv, the power supply of pwm stage is provided by other dc source and it is always on. the following diagram shows an ac/dc part of the lcdtv. the front end is a pfc stage, followed by a pwm stage. a stand along standby converter provides the dc power supply for both pwm and pfc stages. in such conditions, for example, when the over loading protection (olp) occurs, pwm stage will be latched of and it will not recover since it is powered by the standby dc supply. OB2288 overcomes this shortcoming by an internal restart timer. when olp occurs, the timer begins counting. when counting over, the olp states will be cleared. system tends to restart and auto-recover. if olp still exists, then another counting cycle begins. the counting time in OB2288 is 1 second. therefore, the nominal operation of olp is not disturbed. z pin floating and short protection OB2288 provides pin floating protection for ri, sense, fb, etc., and ri pin short protection. in cases when the pin are floating or ri pin is shorted to ground, pwm switching is disabled, thus protect the power system. z overload operation when over load (for exampl e, short circuit) occurs, a fault is detected. if this fault is present for more than 250ms, OB2288 enters an auto-recovery soft burst mode. all pulses are stopped, vdd will drops below uvlo and the controller will try to restart, with the power-on soft start. the smps resumes operation if the fault has gone. otherwise, a burst sequence starts again. z soft start OB2288 features an internal 4ms soft start to soften the constraints occurring in the power supply during startup. it is activated during the power on sequence. as soon as vdd reaches uvlo(exit), the peak current is gradually increased from nearly zero to the maximum clamping level 0.7v. the soft start is also activated during olp sequence. every restart attempt is followed by soft start. z gate drive the pwm output is connected to the gate of an external mosfet for power switch control. too weak the gate drive strength results in higher conduction and switch loss of mosfet, on the anther hand, too strong gate drive output will compromise emi. good tradeoff is achieved through the built-in totem pole gate drive design with right output strength and dead time control. the low idle loss and good emi system design is easy to be achieved with this dedicated control scheme. an internal 17v clamp is added for mosfet gate protection at higher than expected vdd input. on-bright confidential to bona free datasheet http://www.datasheetlist.com/
?on-bright electronics confidential - 11 - ob_doc_ds_8800 OB2288 highly integrated current mode pwm controller package mechanical data 8-pin plastic dip on-bright confidential to bona free datasheet http://www.datasheetlist.com/
?on-bright electronics confidential - 12 - ob_doc_ds_8800 OB2288 highly integrated current mode pwm controller 8-pin plastic sop on-bright confidential to bona free datasheet http://www.datasheetlist.com/
?on-bright electronics confidential - 13 - ob_doc_ds_8800 OB2288 highly integrated current mode pwm controller important notice right to make changes on-bright electronics corp. reserv es the right to make corrections, modifications, enhancements, improvements and other changes to its products and ser vices at any time and to discontinue any product or service without notice. customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. warranty information on-bright electronics corp. warrants performance of its ha rdware products to the speci fications applicable at the time of sale in accordance with its standard warranty. testing and othe r quality control techniques are used to the extent it deems necessary to support this warra nty. except where mandated by government requirements, testing of all parameters of each product is not necessarily performed. on-bright electronics corp. assumes no liability for a pplication assistance or customer product design. customers are responsible for their products and appli cations using on-bright?s components, data sheet and application notes. to minimize the risks associated with customer produc ts and applications, customers should provide adequate design and operating safeguards. life support on-bright electronics corp.?s products are not designe d to be used as components in devices intended to support or sustain human life. on-bright electronics corp. will not be held liable for any damages or claims resulting from the use of its products in medical applications. military on-bright electronics corp.?s products are not designed fo r use in military applications. on-bright electronics corp. will not be held liable for a ny damages or claims r esulting from the use of its products in military applications. on-bright confidential to bona free datasheet http://www.datasheetlist.com/

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