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current-mode pwm controller page 1 pt4201_ds rev en_2.0 pt4201 general description pt4201 is a highly integrated current mode pwm controller providing low standby power and cost effective system solution for the sub 30w flyback converter applications. it is also suitable for high precision and high reliable led lighting applications. it features power saving oper ation at no load or light load condition, pwm frequency is reduced to minimize switching loss and low standby power and high efficiency is thus achieved. pt4201 also features low vdd startup current which also contributes to low standby power. the built in leb on the current sense input removes the signal glitch due to snubber circuit diode reverse recovery thus reduce the external component count and system cost in the design. rich protection is implemented in pt4201 including cycle-by-cycle current limiting (ocp), over load protection (olp), vdd over voltage clamp and under voltage lockout (uvlo). gate drive output is clamped at 18v to protect the power mosfet. by limiting the minimum frequency above 22 khz eliminates the potential audible noise when the system works under light or no load conditions. excellent emi performance is achieved with c.r.powtech proprietary frequency jittering technique together with soft driving control at totem pole gate drive output. the pt4201 is available in sot23-6, sop-8 and dip-8 packages. features z frequency jittering for improved emi performance z green-mode pwm for improved efficiency and minimum standby power design z low start up current 20ua ( typ. 3ua) and low operation current 2ma (typ. 1ma) z current mode operation z leading-edge blanking on current sense input z programmable pwm frequency z constant output power limit for universal ac input z built-in power limit control (olp) z cycle-by-cycle current limiting (ocp) z under voltage lockout (uvlo) z gate output maximum voltage clamped at 18v z totem pole output includes soft driving for better emi applications offline ac/dc flyback converter for z power adapter z open-frame smps z battery charger adapter z 1w-30w hb led lighting. ordering information package temperature range ordering part number transport media marking sot23-6, pb free -40 to 85 pt4201e23f tape and reel 4201 dip8, pb free -40 to 85 pt4201edih tube pt4201 xxxxxx sop8, pb free -40 to 85 PT4201ESOH tape and reel pt4201 xxxxxx note: xxxxxx assembly factory code lot number www.micro-bridge.com
current-mode pwm controller page 2 pt4201_ds rev en_2.0 pt4201 typical applications (switching power supply) typical applications (hb led lighting) pin assignment pt4201 4201 www.micro-bridge.com
current-mode pwm controller page 3 pt4201_ds rev en_2.0 pt4201 pin descriptions names pin no. (sot23-6) pin no. (sop8, dip8) description gnd 1 8 ground fb 2 7 feedback input pin. pwm duty cycle is determined by voltage level into this pin and sense pin voltage level. ri 3 5 internal oscillator frequency setting pin. a resistor connected between ri and gnd sets the pwm frequency. sense 4 4 current sense input pin. connect ed to mosfet current sensing resistor node. vdd 5 2 dc power supply pin. gate 6 1 totem-pole gate drive output for power mosfet. 3, 6 no connection absolute maximum ratings (note1) sym parameter value unit v dd v dd dc supply voltage 30 v v clamp v dd clamp voltage 33 v i dd -clamp v dd dc clamp current 10 ma v fb v fb pin input voltage -0.3~7 v v sense v sense input voltage -0.3~7 v v ri v ri input voltage -0.3~7 v t j min/max operating junction temperature t j -40~150 t stg storage temperature range -55~160 hbm esd capability, hbm model(note 2) 2.0 kv package dissipation rating sym parameter value unit r ja dip8 sop8 sot23-6 90 150 250 /w /w /w operating range sym parameter value unit v dd v dd supply voltage 10~30 v ri ri resistor value 100 kohm t a operating ambient temperature -20~85 note 1: absolute maximum ratings indicate limits beyond which damage to the device may occur. recommended operating range indicates conditions for which the device is functional, but do not guarantee specific performance limits. electrical characteristics state dc and ac electrical specifications und er particular test conditions which guarantee specific performance limits. this assumes that the device is within the operatin g range. specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device performance. www.micro-bridge.com
current-mode pwm controller page 4 pt4201_ds rev en_2.0 pt4201 note 2: human body model, 100pf discharged through a 1.5k ? resistor. electrical characteristics ( t opt =25 , vdd=16v unless specified otherwise ) symbol parameter test condition min typ max unit supply voltage (vdd) v dd_on v dd start-up voltage v dd rising 14.0 15.0 16.0 v v dd_min v dd minimum operating level v dd falling 6.5 7.5 8.5 v v dd_ovp v dd over voltage protection level v dd rising 22.5 24.0 25.5 v v dd_ovp_off v dd over voltage protection release level v dd falling 21.0 22.5 24.0 v v ovp_hys v dd over voltage hysteresis v dd_ovp -v dd_ovp_off 1.5 v v zener v dd pin zener diode clamp voltage i(v dd )=5ma 33 v current into vdd i vdd_start v dd start-up current v dd =13.5v measuring current into v dd 3 20 ua i vdd_oper v dd operating current v dd =16v, ri=100kohm v fb =3v, gate floating 1 ma feed back pin (fb) v ofb v fb open loop voltage v dd =16v, 4.8 v v pl fb over load protection level 3.7 v v gm green mode fb threshold 1.6 v v bm burst mode entering threshold 1.2 v v zd zero duty cycle fb threshold v dd =16v, ri=100kohm 0.70 v t pl_delay over load protection delay time ri=100kohm 32 ms z fb fb pin input impendence 6.0 kohm i fb fb pin supply current fb short to gnd, measuring current flowing from fb pin 0.8 ma oscillator (osc) f osc oscillator frequency ri=100kohm 60 65 70 khz f jit fosc/fosc ri=100kohm -3 3 % t jittring frequency modulation period ri=100kohm 32 ms f min minimum pwm frequency v dd =16v, ri=100kohm 22 khz ri acceptable ri range 50 100 250 kohm www.micro-bridge.com
current-mode pwm controller page 5 pt4201_ds rev en_2.0 pt4201 electrical character istics (continued) symbol parameter test condition min typ max unit f dt oscillator frequency stability at different temperature v dd =16v, ri=100kohm -20 o c 100 o c 2 % f dv oscillator frequency stability at different vdd input level v dd =12~25v, ri=100kohm 2 % pwm section a v pwm input gain v fb / v cs 2.0 v/v t blk leading edge blanking time 300 ns d max pwm maximum duty cycle 75 % d min pwm minimum duty cycle 0 % current sense input (sense) z cs sense input impendence 80 kohm v th_oc ocp threshold at duty=0 fb=3v, v gate <0.3v 0.70 0.75 0.80 v t oc_delay delay time from ocp to gate output off v dd =16v, cs>v th _oc c gate =1000pf 100 ns gate output v ol gate output low level v dd =16v, io=-20ma 0.8 v v oh gate output high level v dd =16v, io=20ma 10 v t_r gate output rising time v dd =16v, cl=1000pf 220 ns t_f gate output falling time v dd =16v, cl=1000pf 70 ns v gmax gate output clamp voltage 18 v www.micro-bridge.com
current-mode pwm controller page 6 pt4201_ds rev en_2.0 pt4201 simplified block diagram operation description with enhanced functions and extremely low start up current and low operating current together with optimized controlling mode, the pt4201 is easy to meet the high performance as well as low standby power requirement in the smps application. its detail features are described as below: startup and uvlo the start up of pt4201 is realized through the current provided by a resistor connecting to hv line charges the capacitor connecting to vdd pin to the start up threshold voltage. as shown below, initially the voltage on chold is below the start up threshold the pt4201 stays in uvlo status. the current supplied by rstart charges the chold thus the voltage on vdd increases. the pt4201 starts to operate when the voltage on vdd reaches v dd_on start up threshold. after startup the pt4201 begins to deliver drive signal on gate and the operating current is supplied by the auxiliary winding of the transformer. since the pt4201 sinks a few macro amperes of current before start up, a large start up resistor could be used in the start up circuit to mini mize standby power. as for the applications with general ac input range a 2mohm 1/8w resistor and a 10uf/50v capacitor compose a simple and reliable start up circuit. www.micro-bridge.com
current-mode pwm controller page 7 pt4201_ds rev en_2.0 pt4201 operating current the pt4201 is fabricated w ith bicmos process, the operating current has been reduced to less 1ma when gate is floating, thus the system efficiency is improved and at the same time, a smaller hold up capacitor can be used to speed up start up progress. feedback and pwm smps application the pt4201 adopts current mode control scheme. the voltage feedback loop is closed by the tl431 and an opto-coupler connected between output node and fb pin, as shown below: a 2.5v reference voltage has been implemented in the tl431, if the divided voltage of r1 and r2 is less than 2.5v tl431 sinks current from vo and the current is transferred to the fb pin by the opto-coupler. the transferred current is loaded by a resistor connected to the internal regulator output so fb pin voltage is determined and thus pwm signal is generated. constant current operation led application : pt4201 senses the led current via an opto-coupler and generates a pwm driving signal to control the led current. reference to the following schematic, current sense resistor r2 and turn on voltage of the opto-coupler determine the led current. when the voltage across r2 turns the opto-coupler on the current of the photo diode of the opto-coupler drives fb pin decrease so the duty cycle of pwm signal is decreased thus the output current is limited. so the output current can be calculated as iout=vonopto/r2. vonopto represents the led turn on voltage of the opto-coupler. energy save operation at light load: generally the smps switching loss is proportional to switching frequency of power mosfet. in order to achieve high conversion ef ficiency when the load decrease pt4201 automatically debase pwm frequency to reduce switching loss. the reduction of the load current results in the decrease of voltage on fb pin, when the voltage on fb pin is lower than 1.6v the pwm frequency will linear ly decrease with v fb until touch bottom which is 1/3 normal operating frequency. if the fb pin voltage drops below the preset level the pt4201 enters burst mode operation, some pwm cycles is skipped to minimize switching loss. moreover if the fb pin voltage falls below zero-duty level the pwm is disabled immediately until it recovers to above zero-duty threshold. led open circuit (led application) when led open circuit occurs, the output voltage rises to break down the zener diode. the inverse current of the zener diode generates a voltage across r1 and r2 to turn on the opto-coupler, thus the voltage on fb pin decrease to reduce the pwm signal duty cycle, so that the power delivered to the output is limited. therefore the system is safe under led open circuit condition. led short circuit (led application) when led short circuit occurs, for the output voltage is low and the output current is limited thus the output power is so small that the system is safe. because the voltage on auxiliary winding is proportion to the output voltage, vdd will then drops due to internal power consumption. when vdd drops below the v dd_min turn-off threshold, the pt4201 will be totally shut down. when this happens, the start up sequence will kick in and vdd is charging up again. when the current sense www.micro-bridge.com
current-mode pwm controller page 8 pt4201_ds rev en_2.0 pt4201 resistor is shorted, because the opto-coupler is turned off the voltage on fb will rise over the protection threshold which is set to be 3.7v, after a delay time the pt4201 will stop delivering pwm signal to protect the system from being damaged. oscillator and frequency jittering the operating frequency can be easily set via a resistor connected to the ri pin and gnd. the relationship between operating frequency and ri follows the expression: fosc=6500/ri. which fosc represents normal operating frequency with unit in khz, and ri with unit in kohm. the frequency jittering is implemented in the pt4201. the oscillation frequency is modulated so that the tone energy is spread out. the spread spectrum minimizes the conduction band emi and therefore reduces system design challenge. care should be considered that the pwm frequency will be reduced to one third of normal operating frequency so a large ri is not recommended because the audible noise maybe exists when the load is too light. current sense and leb: one function of the sense pin is sensing the current of the power mosfet to generate a current slope and the other function is providing cy cle by cycle current limit. the current of the power mosfet is transferred to voltage signal through a resistor connected between source terminal and gnd and feed to sense input. the voltage on sense and fb determines duty cycle of the pwm signal. as for cycle by cycle current limit, at each pwm cycle when the voltage of sense input excess the internal threshold the pwm signal is terminated after a short delay to protect the power mosfet. the relationship between the ocp threshold and the current of power mosfet follows below expression: i oc =voc/rcs; ioc is the current of power mosfet, voc is the threshold of ocp and rcs represents sensing resistor. the internal ocp threshold is modulated by the pwm duty cycle, with zero pwm duty cycle the threshold is 0.75v. a spike is inevitable on the sensed signal on rcs at the instance when the power mosfet is turned on due to the recovery time of the secondary rectifier and the snubber circuit. the leb has been implemented in pt4201, during the leb time the ocp comparator is disabled so the pwm signal can not be terminated by the turn-on spike on the sens ed signal so the external rc filter can be removed. internal slope compensation: to eliminate the potential sub-harmonic oscillation problem when the duty cy cle excess 0.5, the slope compensation has been implem ented in the pt4201. at each pwm duty cycle a constant slope is added to the sensed current ramp so that the system stability is improved. universal input ocp compensation: because there is always a constant delay time td from ocp is triggered to the power mosfet is turned off, the actual current of the mosfet at the instance it is turned off is different from the setting value. taking the below figure as reference, considering the dela y time of td the actual current is: ipeak=ipeak1+islope1*td. islope1=vindc/lpri. with a higher input level the actual ocp current is ipeak=ipeak2+islope2*td, islope2=vindc2/lpri. which lpri represents primary winding inductance of transformer; td is a constant delay time and does not vary with vin. from above www.micro-bridge.com
current-mode pwm controller page 9 pt4201_ds rev en_2.0 pt4201 equations it can be derived that the actual ocp threshold of the power mosfet is always larger than setting value due to the ocp delay time and the difference increases with the increase of vin. in order to compensate the difference ocp threshold in pt4201 has been designed to vary with the duty cycle, it means that a smaller duty cycle results in a smaller ocp threshold. when the input ac voltage increase the duty cycle gets small and the ocp point decrease, thus the actual ocp threshold of power mosfet maintains unchanged in the universal input range. the relationship between ocp threshold voltage and pwm signal duty cycle follows below expression: voc=0.75+0.52*duty duty represents the duty cycle of pwm signal. vdd over voltage protection: when open loop occurs the opto-coupler does not sink current thus the voltage on fb rise and current limit will be triggered. if the load is not large enough the output voltage will increase because of redundant power is delivered to the load. under this condition if the olp is not triggered the output voltage will lost control and the load is in danger of damaged of over voltage. because the voltage on auxiliary winding is proportional to the output voltage the vdd rises with the output. when the volta ge on vdd reaches the ovp threshold the pt4201 stops delivering pwm signal to the power mosfet, voltage on vdd begins to drop due to the internal power consumption, the pt4201 will recover from ovp status when voltage on vdd drops below the ovp release threshold. the ovp cycle will repeat after recovery until if the fault condition is removed. over load protection: the over load protection function (olp) provides another protection to the system from damage when load short circuit or over load occurs. in that condition the voltage on the fb rise, when the v fb excesses 3.7v the pt4201 starts a timer, after a delay time t pl_delay if the fault condition still exists the pwm signal is blocked. vdd will then drops due to internal power consumption. when vdd drops below the v dd_min threshold, the pt4201 will be totally shut down. when this happens, the start up sequence will kick in and vdd is charging up again. gate output the output drives the gate of the power mosfet. the optimized totem-pole type driver offers a good tradeoff between driving ability and emi. additionally the output high level is clamped to 18v by an internal clamp so that power mosfet transistor can be protected against undesirable gate over voltage. a resistor between gate and gnd initials the gate voltage to zero at the off state. www.micro-bridge.com
current-mode pwm controller page 10 pt4201_ds rev en_2.0 pt4201 typical performance characteristics v dd =16v, ri=100kohm, t a =25 if not otherwise noted i dd vs. v dd 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 0.00 2.50 5.00 7.50 10.00 12.50 15.00 v dd (v) i dd (ua) v dd_on vs.temperature 15.0 15.1 15.2 15.3 15.4 15.5 15.6 15.7 -20 0 20 40 60 80 100 120 temp(c) v dd_on (v) i dd_start vs. temperature 0.0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0 -20 0 20 40 60 80 100 120 temp(c) i vdd _ start (ua) v dd_min vs temperature 7.4 7.5 7.6 7.7 7.8 7.9 8.0 8.1 8.2 -20 0 20 40 60 80 100 120 temp(c) v dd_min (v) fosc vs.temperature ri=100k 60.0 61.0 62.0 63.0 64.0 65.0 66.0 67.0 68.0 69.0 70.0 -20 0 20 40 60 80 100 120 tempc fosc(khz) pwm frequency vs. ifb ri=100k 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 440 460 480 500 520 540 560 580 600 ifb(ua) fosc (khz) www.micro-bridge.com
current-mode pwm controller page 11 pt4201_ds rev en_2.0 pt4201 typical performance char acteristics (continued) fosc vs. ri 0 20 40 60 80 100 120 140 50 70 90 110 130 150 170 190 rikohm f osc khz dmax vs.temperature ri=100k 71.0% 72.0% 73.0% 74.0% 75.0% 76.0% 77.0% 78.0% 79.0% -20 0 20 40 60 80 100 120 tempc dmax voc vs. temperature 0.700 0.720 0.740 0.760 0.780 0.800 -20 0 20 40 60 80 100 120 tempc vocv fosc vs. vdd ri=100k 60.00 61.00 62.00 63.00 64.00 65.00 66.00 67.00 68.00 69.00 70.00 10.00 12.00 14.00 16.00 18.00 20.00 22.00 24.00 vddv fosckhz www.micro-bridge.com
current-mode pwm controller page 12 pt4201_ds rev en_2.0 pt4201 package information sot23-6 millimeters inches symbol min max min max a 1.050 1.250 0.041 0.049 a1 0.000 0.100 0.000 0.004 a2 1.050 1.150 0.041 0.045 b 0.300 0.400 0.012 0.016 c 0.100 0.200 0.004 0.008 d 2.820 3.020 0.111 0.119 e 1.500 1.700 0.059 0.067 e1 2.650 2.950 0.104 0.116 e 0.950typ 0.037typ e1 1.800 2.000 0.071 0.079 l 0.700ref 0.028ref l1 0.300 0.600 0.012 0.024 0 8 0 8 d b e1 e e e1 a a2 a1 l c l1 0.2 www.micro-bridge.com
current-mode pwm controller page 13 pt4201_ds rev en_2.0 pt4201 package information sop8 l dimensions in millimeter s dimensions in inch symbol min max min max a 1.350 1.750 0.053 0.069 a1 0.100 0.250 0.004 0.010 a2 1.350 1.550 0.053 0.061 b 0.330 0.510 0.013 0.020 c 0.170 0.250 0.006 0.010 d 4.700 5.100 0.185 0.200 e 3.800 4.000 0.150 0.157 e1 5.800 6.200 0.228 0.244 e 1.270(bsc) 0.050(bsc) l 0.400 1.270 0.016 0.050 0 8 0 8 www.micro-bridge.com
current-mode pwm controller page 14 pt4201_ds rev en_2.0 pt4201 package information dip8 dimensions in millimeters dimensions in inches symbol min max min max a 3.710 4.310 0.146 0.170 a1 0.510 0.020 a2 3.200 3.600 0.126 0.142 b 0.380 0.570 0.015 0.022 b1 1.524 (bsc) 0.060 (bsc) c 0.204 0.360 0.008 0.014 d 9.000 9.400 0.354 0.370 e 6.200 6.600 0.244 0.26 e1 7.320 7.920 0.288 0.312 e 2.540(bsc) 0.100(bsc) l 3.000 3.600 0.118 0.142 e2 8.400 9.000 0.331 0.354 www.micro-bridge.com

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