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preliminary datasheet current mode pwm controller for bjt ap3720 jul. 2009 rev. 1. 0 bcd semiconductor manufacturing limited 1 general description the ap3720 is a low startup current, current mode pwm controller with green -mode operation. the pwm switching frequency at normal operation is 65k, but when the output power drops below the specifically level, the device enters the frequency-drop mode and the typical operating frequency is 20khz (no audible noise). additionally, when the load drops to a very low level or zero, the ic operates in so called ?burst mode? to minimize switching loss. the ic integrated a lot of functions such as the lead-edge blanking (leb) of the current sensing, internal slope compensatio n, line compensation, and several protection features. the protection functions include cycle-by-cycle current limit (ocp), vcc over voltage protection (ovp), otp and olp. the ap3720 is available in dip-8 and soic-8 packages. features ? low startup current 2.5 a and low operating current (1.2ma) ? off-line converter applied in sub 25w range ? skip cycle mode achi eves low standby power (<200mw) ? cycle-by-cycle power limited ? frequency-drop mode ? soft start with 2ms ? programmable drive current for bjt ? leading edge blanking ? pre-shutdown decreases turn-off losses ? reliable protection: accurate ocp with line compensation short circuit protection over voltage protection for vcc hysteretic thermal shutdown protection applications ? stb ? cable modem ? adsl modem ? dvd recorder figure 1. package types of ap3720 dip-8 soic-8
preliminary datasheet current mode pwm controller for bjt ap3720 jul. 2009 rev. 1. 0 bcd semiconductor manufacturing limited 2 pin configuration p package m package (dip-8) (soic-8) line nc fb bias 1 2 3 4 8 7 6 5 cs gnd drv vcc 1 2 3 4 8 7 6 5 line nc fb bias cs gnd drv vcc figure 2. pin configuration of ap3720 (top view) pin description pin number pin name function 1 line line compensation for olp 2 nc no connection 3 fb connect opto-coupler to this pin. the voltage of fb controls the mode of operation in one of the three modes: burst mode, frequency-drop mode (20khz) and normal mode ( 65khz). when the voltage of fb reaches a limit-point, the syst em enters the olp mode 4 bias this pin sets the driver current inside ap3720 with an external resistor to gnd 5 vcc this pin is the positive supply voltage input. during start up, the power is supplied from line voltage. when v cc reaches 20v, the system begins running and the power is supplied from the auxiliary transformer winding 6 drv this pin supplies the drive current for the external power npn switch 7 gnd this pin is the control ground 8 cs this pin senses the primary current and routes it to internal comparator. by changing the value of the sense resistor, the primary peak current set point is adjusted according to the output power demand
preliminary datasheet current mode pwm controller for bjt ap3720 jul. 2009 rev. 1. 0 bcd semiconductor manufacturing limited 3 functional block diagram skip olp vf4 vf2 vf3 duty pwm comp cs fb slope compensation r s osc 65k/20k q drive ocp v2 comp comp comp comp line compensation drv regulator &uvlo internal supply vcc gnd line olp otp fault protect logic skip vref&vbias vf4 vf3 vf2 k1 ovp v1 comp ovp bias 1 3 4 5 6 7 8 figure 3. functional block diagram of ap3720 ordering information ap3720 - package temperature range part number marking id packing type dip-8 AP3720P-G1 AP3720P-G1 tube soic-8 -40 to 85 c ap3720mtr-g1 3720m-g1 tape & reel bcd semiconductor's pb-free products, as designated with "g1" suffix in the part number, are rohs compliant and green. g1: green circuit type package p: dip-8 m: soic-8 tr: tape and reel blank: tube
preliminary datasheet current mode pwm controller for bjt ap3720 jul. 2009 rev. 1. 0 bcd semiconductor manufacturing limited 4 absolute maximum ratings (note 1) parameter symbol value unit supply voltage v cc -0.3 to 28 v voltage at drv, fb, cs, bias, line -0.3 to 7 v output current at drv i drv internally limited a dip-8 1.35 power dissipation at t a =25oc p d soic-8 0.55 w operating junction temperature t j 160 oc storage temperature t stg -65 to 150 oc lead temperature (soldering, 10 sec) t lead 300 oc dip-8 83 thermal resistance (junction-to-ambient) ja soic-8 186 oc/w esd (machine model) 400 v note 1: stresses greater than those listed under ?absolute maximum ratings? 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 co nditions? is not implied. exposure to ?absolute maximum ratings? for extended periods may affect device reliability. recommended operating conditions parameter symbol min max unit supply voltage v cc 12 18 v ambient temperature t a -40 85 oc
preliminary datasheet current mode pwm controller for bjt ap3720 jul. 2009 rev. 1. 0 bcd semiconductor manufacturing limited 5 electrical characteristics v cc =15v, t a =25c, unless otherwise specified. parameter conditions min typ max unit supply voltage ( vcc pin ) startup current v cc =15v 2.5 8 a operating current v fb =v cs =0v 1.2 2.5 ma uvlo (on) 18.5 20 21.5 v uvlo (off) 7.1 8 8.9 v vcc ovp 26.5 28.5 v pwm section / oscillator section maximum duty cycle 67 75 83 % normal frequency v fb =3v 60 65 70 khz green frequency v fb =2v 20 khz from 65k to 20k 64 ms frequency switch delay time from 20k to 65k 0 ms frequency temperature stability -40oc to 85oc 5 8 % frequency voltage stability v cc =8v to 18v 1.5 3 % current sense section ( cs pin ) maximum cs voltage v line =0.95v 0.983 1.032 1.081 v line compensation coefficient 4.6 9.5 % leb time 250 350 400 ns soft start time 2 ms feedback input section ( fb pin ) the ratio of fb to cs g fb 2.5 3 3.5 v/v input impedance r fb 7 10 13 k ? source current i fb -1 -0.5 ma output section ( gate pin ) output maximum current r bias =1m 32 ma output sink current v fb =v cs =0v 0.5 ma protection section olp delay time v fb =5.1v 64 ms shutdown temperature 160 oc
preliminary datasheet current mode pwm controller for bjt ap3720 jul. 2009 rev. 1. 0 bcd semiconductor manufacturing limited 6 1.45v 4.85v v fb < 1.45v monitor v fb soft start (2ms) start vcc > 20v control flow chart
preliminary datasheet current mode pwm controller for bjt ap3720 jul. 2009 rev. 1. 0 bcd semiconductor manufacturing limited 7 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 52 53 54 55 56 57 58 59 60 61 62 63 64 65 temperature ( o c) the highest f sw the lowest f sw the average f sw switch frequency (khz) -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 temperature ( o c) start up current ( a) 0 500 1000 1500 2000 2500 3000 3500 0 20 40 60 80 100 drive current (ma) r bias (k ? ) -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 16.0 16.5 17.0 17.5 18.0 18.5 19.0 19.5 20.0 20.5 21.0 temperature ( o c) the highest f sw the lowest f sw the average f sw switch frequency (khz) typical performance characteristics figure 4. drive current vs. r bias figure 5. start-up current vs. temperature figure 6. switch frequency (65k) vs. temperature figure 7. switch frequency (20k) vs. temperature
preliminary datasheet current mode pwm controller for bjt ap3720 jul. 2009 rev. 1. 0 bcd semiconductor manufacturing limited 8 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 320 325 330 335 340 345 350 355 360 365 370 temperature ( o c) leb (ns) typical performance characteristics (continued) figure 8. leb vs. temperature operation description figure 9. operation diagram of ap3720
preliminary datasheet current mode pwm controller for bjt ap3720 jul. 2009 rev. 1. 0 bcd semiconductor manufacturing limited 9 operation description (continued) start sequence when the vcc capacitor reaches the uvlo (on) level (typically 20v), the controller runs. at this time, vcc capacitor supplies the controller and the auxiliary supply takes over before vcc collapses below uvlo (off) . soft start the internal soft start function is activated at start-up with a duration of 2ms (typical). the current sense compensation starts from 1.0v and slowly decreases to zero at the end of the 2ms duration. this function is activated at each auto-restart attempt due to olp or tsd condition. the feature also helps minimize output overshoot and prevents saturation of transformer during start-up. fb pin operation the ap3720 can automatically adjust the operating mode according to the load ing condition. the voltage of fb controls the mode of operation in one of the three modes: burst mode, frequency-drop mode (20khz) and normal mode (65khz). to prevent saturation of transformer and achieve good transient load performance, the sw itch from frequency-drop mode to normal mode occurs with no delay time and that from normal mode to frequency-drop mode occurs with 64ms delay time when the load condition changes. burst mode operation at zero load or light load condition, majority of the power dissipation is in proportion to the number of switch events within a fixed period of time. to reduce the loss in this situation, the device enters burst mode control which makes some switching cycle skip when v fb drops below the burst mode threshold level. frequency-drop mode (20khz) when the output power drops below a specific level, the device enters the frequency-drop mode and the typical operating frequency is 20khz. in this mode, the system efficiency at specific load will improve obviously. normal mode (65khz) at the higher load, the de vice operates in normal mode and the frequency is 65khz (typical). cycle-by-cycle current limit the cycle terminates when the cs voltage exceeds 1.074v. the ap3720 operates as a current mode controller, whereby output switch conduction is initiated by the oscillator and terminated when the peak inductor current reaches the threshol d level established by v fb . the inductor current is converted to a voltage by inserting the ground referenced sense resistor r s in series with the emitter of the power transistor. when the power supply output is overload or the control loop is open, the current sense comparator threshold will be internally clamped to about 1.074v. therefore the maximum peak inductor current is: s line pk r v k i ? ? = 074 . 1 (max) ( k=0.0444 ) leading edge blanking (leb) at the instant the power transistor is turned on, there usually exists a high current spike through the bjt, caused by primary-side capacitance and secondary-side rectifier reverse recovery. excessive voltage across the r s can lead to incorrect feedback operation in the current mode pwm control. to counter this effect, the ap3720 employs a leading edge blanking (leb) circuit. this circuit inhibits the pwm comparator for a short time (t leb ) after the bjt is turn on. line compensation the ap3720 has an adjust able line compensation so that achieves constant output power limit over the universal input voltage range. drive current control the ap3720 drive current is programmable through an external resistor to gnd (see figure 4).
preliminary datasheet current mode pwm controller for bjt ap3720 jul. 2009 rev. 1. 0 bcd semiconductor manufacturing limited 10 operation description (continued) protection circuit the ap3720 has several self-protective functions such as over load protection (olp), open loop protection, over voltage protection for vcc, thermal shutdown (tsd). because these protection circuits are fully integrated into the ic without external components, the reliability can be improved without increasing cost. once the fault condition occurs, switching is terminated and the power transistor remains off. this causes v cc to fall. when v cc reaches the uvlo stop vo ltage of 8v, the current consumed by the ap3720 decreases to the start-up current (typically 2.5 a) and the current supplied from the dc link charges the vcc capacitor. when v cc reaches the start voltage of 20v, the ap3720 resumes its normal operation. in this manner, the auto-restart can alternately enable and disable the switching of the power transistor until the fault condition is eliminated. over load protection: in this situation, the protection circuit should be activated to protect the smps. however, even when the smps is in the normal operation, the over load protection circuit can be activated during the load transition. to avoid this undesired operation, the over load protection circuit is designed to be activated after a specified time (typically 64ms) to determine whether it is a transient situation or an overload situation. because of the cycle-by-cycle current limit, the maximum peak current through the bjt is limited, and therefore the maximum input power is restricted. if the output consumes exceeds this maximum power, the voltage decreases below the rated voltage. this reduces the current through the opto-coupler led, which also reduces the opto-coupler transistor current, thus increasing v fb . if v fb exceeds 4.85v and holds the situation beyond 64ms, the over load protection circuit is activated. open loop protection: in this abnormal situation, olp or ovp will be activated. over voltage protection: if the control loop is open, the current through the opto-coupler transistor becomes almost zero. then v fb climbs up to the over load situation and the over load protection is activated. but maybe the output voltage exceed the rated voltage before the over load protection is activated, resulting in the breakdown of the devices in the secondary side and the primary side. to prevent this situation, an over voltage protection circuit is employed. in general, v cc is proportional to the output voltage. if v cc exceeds 26.5v, an ovp circuit is activated resulting in the termination of the switching operation. to avoid undesired activation of ovp during normal operation, v cc should be designed to be below 20v. thermal shutdown thermal shutdown is provided by a precision analog circuit that turns the power transistor off when the junction temperature exceeds the thermal shutdown temperature (typically 160 oc ). when the junction temperature drops about the hysteretic temperature, normal operation resumes.
preliminary datasheet current mode pwm controller for bjt ap3720 jul. 2009 rev. 1. 0 bcd semiconductor manufacturing limited 11 mechanical dimensions dip-8 unit: mm(inch) r0.750(0.030) 0.254(0.010)typ 0.130(0.005)min 8.200(0.323) 9.400(0.370) 0.204(0.008) 0.360(0.014) 7.620(0.300)typ 5 0.700(0.028) 9.000(0.354) 9.400(0.370) 3.710(0.146) 4.310(0.170) 3.000(0.118) 3.600(0.142) 0.360(0.014) 0.560(0.022) 2.540(0.100) typ 6.200(0.244) 6.600(0.260) 3.200(0.126) 3.600(0.142) 0.510(0.020)min 3.000(0.118) depth 0.100(0.004) 0.200(0.008) 1.524(0.060) typ note: eject hole, oriented hole and mold mark is optional.
preliminary datasheet current mode pwm controller for bjt ap3720 jul. 2009 rev. 1. 0 bcd semiconductor manufacturing limited 12 mechanical dimensions (continued) soic-8 unit: mm(inch) 1 5 1.000(0.039) 0.330(0.013) 0.510(0.020) 1.350(0.053) 1.750(0.069) 0.100(0.004) 0.300(0.012) 0.900(0.035) 0.800(0.031) 0.200(0.008) 3.800(0.150) 4.000(0.157) 1.270(0.050) typ 0.190(0.007) 0.250(0.010) 5.800(0.228) 6.200(0.244) 0.675(0.027) 0.725(0.029) 0.320(0.013) 0.450(0.017) 0.800(0.031) 4.700(0.185) 5.100(0.201) note: eject hole, oriented hole and mold mark is optional.
important notice bcd semiconductor manufacturing limited reserves the right to make changes without further not ice to any products or specifi- cations herein. bcd semiconductor manufacturing limited does not as sume any responsibility for us e of any its products for any particular purpose, nor does bcd semiconductor manufacturi ng limited assume any liability aris ing out of the application or use of any its products or circui ts. bcd semiconductor manufacturing limited does not convey any license under its patent rights or other rights nor the rights of others. - wafer fab shanghai sim-bcd semiconductor manufacturing co., ltd. 800 yi shan road, shanghai 200233, china tel: +86-21-6485 1491, fax: +86-21-5450 0008 main site regional sales office shenzhen office shanghai sim-bcd semiconductor manuf acturing co., ltd., shenzhen office unit a room 1203, skyworth bldg., gaoxin ave.1.s., nanshan district, shenzhen, china tel: +86-755-8826 7951 fax: +86-755-8826 7865 taiwan office bcd semiconductor (taiwan) company limited 4f, 298-1, rui guang road, nei-hu district, taipei, taiwan tel: +886-2-2656 2808 fax: +886-2-2656 2806 usa office bcd semiconductor corp. 30920 huntwood ave. hayward, ca 94544, usa tel : +1-510-324-2988 fax: +1-510-324-2788 - headquarters bcd semiconductor manufacturing limited no. 1600, zi xing road, shanghai zizhu sc ience-based industrial park, 200241, china tel: +86-21-24162266, fax: +86-21-24162277 bcd semiconductor manufacturing limited important notice bcd semiconductor manufacturing limited reserves the right to make changes without further not ice to any products or specifi- cations herein. bcd semiconductor manufacturing limited does not as sume any responsibility for us e of any its products for any particular purpose, nor does bcd semiconductor manufacturi ng limited assume any liability aris ing out of the application or use of any its products or circui ts. bcd semiconductor manufacturing limited does not convey any license under its patent rights or other rights nor the rights of others. - wafer fab shanghai sim-bcd semiconductor manufacturing limited 800, yi shan road, shanghai 200233, china tel: +86-21-6485 1491, fax: +86-21-5450 0008 bcd semiconductor manufacturing limited main site regional sales office shenzhen office shanghai sim-bcd semiconductor manuf acturing co., ltd. shenzhen office advanced analog circuits (shanghai) corporation shenzhen office room e, 5f, noble center, no.1006, 3rd fuzhong road, futian district, shenzhen 518026, china tel: +86-755-8826 7951 fax: +86-755-8826 7865 taiwan office bcd semiconductor (taiwan) company limited 4f, 298-1, rui guang road, nei-hu district, taipei, taiwan tel: +886-2-2656 2808 fax: +886-2-2656 2806 usa office bcd semiconductor corporation 30920 huntwood ave. hayward, ca 94544, u.s.a tel : +1-510-324-2988 fax: +1-510-324-2788 - ic design group advanced analog circuits (shanghai) corporation 8f, zone b, 900, yi shan road, shanghai 200233, china tel: +86-21-6495 9539, fax: +86-21-6485 9673 bcd semiconductor manufacturing limited http://www.bcdsemi.com bcd semiconductor manufacturing limited

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