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r ev . 2.0 iw1692 p age 1 f ebr ua r y 13, 2012 1.0 features ? primary-side feedback eliminates opto-isolators and simplifes design ? multi-mode operation for highest overall effciency ? built-in cable drop compensation ? v ery tight output voltage regulation ? no external loop compensation components required ? complies with cec/epa/iec no load power consumption and average effciency regulations ? built-in output constant-current control with primary-side feedback ? low start-up current (10 a typical) ? built-in soft start ? built-in short circuit protection ? ac line under/overvoltage and output overvoltage protection ? 40 khz pwm switching frequency ? pfm operation at light load ? built-in i sense pin short protection ? space-saving sot -23 package figure 2.0.1 iw1692 typical application circuit 2.0 description the iw1692 is a high performance ac/dc power supply controller which uses digital control technology to build peak current mode pwm fyback power supplies. the device provides high effciency along with a number of key built-in protection features while minimizing the external component count and bill of material cost. the iw1692 removes the need for secondary feedback circuitry while achieving excellent line and load regulation. it also eliminates the need for loop compensation components while maintaining stability over all operating conditions. pulse-by-pulse waveform analysis allows for a loop response that is much faster than traditional solutions, resulting in improved dynamic load response. the built-in power limit function enables optimized transformer design in universal off-line applications and allows for a wide input voltage range. the low start-up power and pfm operation at light load ensure that the iw1692 is ideal for applications targeting the newest regulatory standards for standby power. 3.0 applications ? low power ac/dc adapter/chargers for cell phones, pdas, digital still cameras ? standby supplies for televisions, dvds, set-top boxes and other consumer electronics l n v out rtn + + + + u1 iw1692 v cc i sense v in output gnd v sense 4 2 6 5 3 1 iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 2 f ebr ua r y 13, 2012 pin # name type pin description 1 v sense input voltage sense input from the auxiliary winding. 2 gnd ground ground connection. 3 output output gate drive output for the external power mosfet switch. 4 v cc input supply voltage. 5 i sense input primary current sense. used for cycle-by-cycle peak current control and limit. 6 v in input senses average rectifed input voltage. parameter symbol value units dc supply voltage range (pin 4, i cc = 20ma max) v cc -0.3 to 18 v dc supply current at v cc pin i cc 20 ma output (pin 3) -0.3 to 18 v v sense input (pin 1, i vsense 10 ma) -0.7 to 4.0 v i sense input (pin 5) -0.3 to 4.0 v v in input (pin 6) -0.3 to 18 v power dissipation at t a 25c p d 400 mw maximum junction temperature t j (max) 125 c storage temperature t stg C65 to 150 c lead temperature during ir refow for 15 seconds t lead 260 c thermal resistance junction-to-ambient ja 240 c/w esd rating per jedec jesd22-a114 (hbm) 2,000 v latch-up test per jedec 78 100 ma 5.0 absolute maximum ratings absolute maximum ratings are the parametric values or ranges which can cause permanent damage if exceeded. for maximum safe operating conditions, refer to electrical characteristics in section 6.0. 4.0 pinout description iw1692 v sense gnd output v in i sense v cc 1 2 3 6 5 4 iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 3 f ebr ua r y 13, 2012 v cc = 12 v, -40c t a 85c, unless otherwise specifed (note 1) parameter symbol test conditions min typ max unit v in section (pin 6) start-up voltage threshold v inst t a = 25c, positive edge 366 407 448 mv start-up current i inst v in = 10 v, c vcc = 10 f r output = 10 kw to gnd 10 15 a shutdown low voltage threshold v uvdc t a = 25c 216 240 264 mv shutdown high voltage threshold v ovdc t a = 25c 1.834 1.988 2.123 v input impedance z in after start-up 20 kw v sense section (pin 1) input leakage current i bvs v sense = 2 v 1 a nominal voltage threshold v sense(nom) t a =25c, negative edge 1.523 1.538 1.553 v output ovp threshold (1692-00) v sense(max) t a =25c, negative edge 1.649 1.700 1.751 v output section (pin 3) output low level on-resistance r ds(on)lo i sink = 5 ma 45 100 w output high level on-resistance r ds(on)hi i source = 5 ma 65 100 w rise time (note 2) t r t a = 25c, c l = 330 pf 10% to 90% 40 75 ns fall time (note 2) t f t a = 25c, c l = 330 pf 90% to 10% 40 75 ns output switching frequency f s i load > 15% of maximum 36 40 44 khz v cc section (pin 4) maximum operating voltage v cc(max) 16 v start-up threshold v cc(st) v cc rising 11.0 12.0 13.2 v undervoltage lockout threshold v cc(uvl) v cc falling 5.5 6.0 6.6 v operating current i ccq c l = 330 pf, v sense = 1.5 v 2.5 3.5 ma i sense section (pin 5) peak limit threshold v peak 1000 mv cc limit threshold v cc-th 900 mv 6.0 electrical characteristics notes: note 1. adjust v cc above the start-up threshold before setting at 12 v. note 2. these parameters are not 100% tested, guaranteed by design and characterization. iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 4 f ebr ua r y 13, 2012 7.0 typical performance characteristics 12.4 12.3 12.2 12.1 12.0 v cc start-up threshold (v) ambient temperature (c) -50 -25 0 25 50 75 100 figure 7.0.3 start-up threshold vs. temperature 2.015 2.010 2.005 2.000 1.995 internal reference voltage (v) ambient temperature (c) -50 -25 0 25 50 75 100 v cc = 12 v figure 7.0.4 internal reference vs. temperature 2.8 2.6 2.4 2.2 2.0 1.8 1.6 v cc supply current (ma) load capacitance (pf) 0 200 400 600 800 1000 v cc = 12 v t a = 25 figure 7.0.1 supply current vs. load capacitance 44 42 40 38 36 switching frequency (khz) ambient temperature (c) -50 -25 0 25 50 75 100 v cc = 12 v figure 7.0.2 switching frequency vs. temperature iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 5 f ebr ua r y 13, 2012 8.0 functional block diagram 9.0 theory of operation ? + v in gnd v insw v cc 2 v sense v fb v vms v ipk output i sense 5 1.0 v 0.2 v ~ 0.9 v v in_a 0.2 v ~ 2.0 v i peak adc v ocp ? start-up dac ? + 1 6 4 digital logic control signal conditioning gate driver 3 v insw figure 8.0.1 iw1692 functional block diagram the iw1692 is a digital controller which uses a new, proprietary primary-side control technology to eliminate the opto-isolated feedback and secondary regulation circuits required in traditional designs. this results in a low-cost solution for low power ac/dc adapters. the core pwm processor uses fxed-frequency discontinuous conduction mode (dcm) operation at heavy load and switches to variable frequency operation at light loads to maximize effciency. furthermore, iwatts digital control technology enables fast dynamic response, tight output regulation, and full featured circuit protection with primary-side control. referring to the block diagram in figure 8.0.1, the digital logic control generates the switching on-time and off-time information based on the line voltage and the output voltage feedback signal. the system loop is internally compensated inside the digital logic control, and no external analog components are required for loop compensation. the iw1692 uses an advanced digital control algorithm to reduce system design time and improve reliability. furthermore, accurate secondary constant-current operation is achieved without the need for any secondary-side sense and control circuits. the iw1692 uses pwm mode control at higher output power levels and switches to pfm mode at light load to minimize power dissipation. additional built-in protection features include overvoltage protection (ovp), output short circuit protection (scp), ac low line brown out, over current protection, single pin fault protection and i sense fault detection. iwatts digital control scheme is specifcally designed to address the challenges and trade-offs of power conversion design. this innovative technology is ideal for balancing new regulatory requirements for green mode operation with more practical design considerations such as lowest possible cost, smallest size and high performance output control. iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 6 f ebr ua r y 13, 2012 v cc v cc(st) off enable start-up sequencing 200s v in v in impedance = 20k ? v insw on figure 9.2.1 start-up sequencing diagram 9.3 understanding primary feedback figure 9.3.1 illustrates a simplifed fyback converter. when the switch q1 conducts during t on , the current i g is directly drawn from rectifed sinusoid v g . the energy e g is stored in the primary winding. the rectifying diode d1 is reverse biased and the load current i o is supplied by the secondary capacitor c o . when q1 turns off, d1 conducts and the stored energy e g (t) is delivered to the output. + v in (t) t s (t) i o v o n p n s n aux d1 q1 v aux c o v g (t) i g (t) + C i in (t) i d (t) figure 9.3.1 simplifed flyback converter in order to regulate the output voltage within a tight specifcation, the information about the output voltage and load current needs to be accurately sensed. in the dcm fyback converter, this information can be read via the auxiliary winding or the primary magnetizing inductance (l m ). during the q 1 on-time, the load current is supplied from the output flter capacitor c o . the voltage across the primary winding is v g (t) , assuming the voltage dropped across q 1 is zero. the current in q 1 ramps up linearly at a rate of: () () gg m di t v t dt l (9.1) 9.1 pin detail pin 1 C v sense sense signal input from auxiliary winding. this provides the secondary voltage feedback used for output regulation. pin 2 C gnd analog, digital and power ground. pin 3 C output gate drive signal for the external power mosfet switch. pin 4 C v cc power supply for the controller during normal operation. the controller starts up when v cc reaches 12 v (typical) and shuts-down when the v cc voltage is below 6 v (typical). a 100 nf decoupling capacitor should be connected between the v cc pin and gnd. pin 5 C i sense primary current sense. pin 6 C v in sense signal input representing the instantaneous rectifed line voltage. v in is used for line regulation. the internal impedanace is 20 k w and the scale factor is 0.0043. it also provides input undervoltage and overvoltage protection. this pin also provides the supply current to the ic during start-up. 9.2 start-up prior to start-up the v in pin charges up the v cc capacitor, through the diode between v in and v cc . when v cc is fully charged to a voltage higher than v cc(st) threshold, then the v in_sw turns on and the analog-to-digital converter begins to sense the input voltage. the iw1692 commences soft-start function as soon as the voltage on v in pin is above v inst . the iw1692 incorporates an internal soft-start function. the soft-start time is set at 3.0 ms. once the v in pin voltage has reached its turn-on threshold, the iw1692 starts switching, but limits the on-time to a percentage of the maximum on- time. during the frst 1 ms, the on-time is limited to 25%. during the next 1 ms, the on-time is limited to 50% and during the last 1 ms, the on-time is limited to 75%. if at any time the v cc voltage drops below v cc(uvl) threshold then all the digital logic is fully reset. at this time the v in_sw switches off so that the v cc capacitor can be charged up again. iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 7 f ebr ua r y 13, 2012 at the end of on-time, the current has ramped up to: () () () g on g m vt t t it l = (9.2) this current represents a stored energy of: 2 () 2 m gg l e it = (9.3) when q 1 turns off, i g (t) in l m forces a reversal of polarities on all windings. ignoring the communication-time caused by the leakage inductance l k at the instant of turn-off, the primary current transfers to the secondary at an amplitude of: () () p dg s n it it n = (9.4) assuming the secondary winding is master, the auxiliary winding is slave. v aux 0v v aux = -v g x n aux n p see equation 9.5 figure 9.3.2 auxiliary voltage waveforms the auxiliary voltage is given by: () aux aux o s n v vv n = +? (9.5) and refects the output voltage as shown in figure 9.3.2. the voltage at the load differs from the secondary voltage by a diode drop and ir losses. the diode drop is a function of current, as are ir losses. thus, if the secondary voltage is always read at a constant secondary current, the difference between the output voltage and the secondary voltage is a fxed v . furthermore, if the voltage can be read when the secondary current is small, v is small. the real-time waveform analyzer in the iw1692 reads this information cycle by cycle and then generates a feedback voltage v fb . the v fb signal precisely represents the output voltage and is used to regulate the output voltage. 9.4 understanding cc and cv mode the constant current mode (cc mode) is useful in battery charging applications. during this mode of operation the iw1692 will regulate the output current at a constant maximum level regardless of the output voltage drop, while avoiding continuous conduction mode. to achieve this regulation the iw1692 senses the load current indirectly through the primary current. the primary current is detected by the i sense pin through a resistor from the mosfet source to ground (r ss ). this resistor value is given by: 2 c ss outmax nk r i = (9.6) n is the ratio of primary turns to secondary turns of the transformer and k c is given as 0.264 v. 9.5 constant voltage operation after soft-start is completed, the digital control block measures the output conditions. if the i sense signal is not consistently over 0.9 v, then the device will operate in constant voltage mode. if no voltage is detected on v sense after 20 pulses, it is assumed that the auxiliary winding of the transformer is either open or shorted and the iw1692 shuts down. as long as calculated t on for cv is less than the t on in cc the ic operates in constant voltage mode. 9.6 constant current operation the iw1692 has been designed to work in constant-current mode for battery charging applications. if the output voltage drops, but does not go below 20% of the nominal designed value, the device operates in this mode. iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 8 f ebr ua r y 13, 2012 output voltage output current i out(cc) v nom cv mode cc mode figure 9.6.1 modes of operation 9.7 variable frequency mode the iw1692 is designed to operate in discontinuous conduction (dcm) mode at a fxed frequency of 40 khz in both cc and cv modes. to avoid operation in continuous conduction (ccm) mode, the iw1692 checks for the falling edge of the v sense input on every cycle. if a falling edge of v sense is not detected during the normal 25s period, the switching period is extended until the falling edge v sense does occur. if the switching period reaches 75s without v sense being detected, the iw1692 immediately shuts off. 9.8 pfm mode at light load the iw1692 operates in a fxed frequency pwm mode when i out is greater than approximately 5% of the specifed maximum load current. as the output load i out is reduced, the on-time t on is decreased. at the moment that t on drops below t on_min , the controller transitions to pulse frequency modulation (pfm) mode. thereafter, the on-time is modulated by the line voltage and the off-time is modulated by the load current. the device automatically returns to pwm mode when the load current increases. 9.9 internal loop compensation the iw1692 incorporates an internal digital error amplifer with no requirement for external loop compensation. the loop stability is guaranteed by design to provide at least 45 degrees of phase margin and C20db of gain margin. 9.10 voltage protection functions the iw1692 includes functions that protect against input and output overvoltage. the input voltage is monitored by the v in pin and the output voltage is monitored by the v sense pin. if the voltage at these pins exceed their undervoltage or overvoltage thresholds for more than 6 cycles, the iw1692 shuts-down immediately. however, the ic remains biased which discharges the v cc supply. once v cc drops below the uvlo threshold, the controller resets itself and then initiates a new soft-start cycle. the controller continues attempting start-up, but does not fully start-up until the fault condition is removed. the output voltage can be high enough to damage the output capacitor when the feedback loop is broken. the iw1692 uses the primary feedback only with no secondary feedback loop. when the v sense pin is shorted to gnd (by shorting/open sense resistor). the controller will shut off with 6 consecutive pulses after start-up. 9.11 cable drop compensation the iw1692-30 incorporates an innovative method to compensate for any ir drop in the secondary circuitry including cable and cable connector. a 5 w ac adapter with 5 vdc output has 6% deviation at 1 a load current due to the drop across the dc cable without cable compensation. the iw1692-30 cancels this error by providing a voltage offset to the feedback signal based on the amount of load current detected. the iw1692-30 has 300mv of cable drop compensation at maximum current. the IW1692-00 does not include any cable drop compensation. iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 9 f ebr ua r y 13, 2012 10.0 design example 10.1 design procedure this design example gives the procedure for a fyback converter using iw1692. refer to fgure 12.0.1 for the application circuit. the design objectives for this adapter are given in table 10.1. it meets ul, iec, and cec requirements. determine output voltage d etermine the design specifications (vout, iout_max, vin_max, vin_min, efficiency, and ripple) determine turns ratio determine input bulk capacitance determine current sensing resistor determine magnetizing inductance determine primary turns determine secondary turns can you wind this transformer ? determine bias turns determine vsense turns and resistors determine output capacitance determine snubber network determine ton delay compensation finish yes no determine rvin resistors figure 10.0.1 iw1692 design flow chart parameter symbol range input voltage v in 85 - 264 v rms frequency f in 47 - 64 hz no load input p in 200 mw output voltage v out_pcb 4.95 - 5.05 v output current i out 1 a output ripple v ripple <100 mv power out p out 5 w cec effciency h 65% table 10.1 iw1692 design specifcation table 10.2 output voltage use equation 10.1 for v out in the following equations, where v fd is the forward voltage of the output diode: () out out pcb fd vv v = + since no cable is used and the forward drop on the output diode (v fd ) is 500 mv, v out is 5.0 v. 10.3 input selection v in resistors are chosen primarily to scale down the input voltage for the ic. the scale factor for the input voltage in the ic is 0.0043 and the internal impedance of this pin is 20 k. therefore, the v in resistors should equate to: 20 20 4.63 0.0043 vin k r km w = ? w= w from equation 10.2, ideally r vin should be 4.63 m because r10 and r11 add up to approximately 4.6 m. by selecting the value of r vin , the (v in ?t on ) max_limit and (v in ?t on ) pfm are determined: ( ) _ 900 s 0.0043 20 20 in on max limit vin v vt k rk ?m ?= ?? w ?? +w ?? ( ) 185 s 0.0043 20 20 in on pfm vin v vt k rk ?m ?= ?? w ?? +w ?? keep in mind by changing r vin to be something other than 4.63 m the minimum and maximum input voltage for start- up will also change. iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 10 f ebr ua r y 13, 2012 since the iw1692 uses the exact scaled value of v in for its calculations, c6 should be included to flter out any noise that may appear on the v in signal. this is especially important for line-in surge conditions. 10.4 turns ratio the maximum allowable turns ratio between the primary and secondary winding is determined by the minimum detectable reset time of the transformer, during pfm mode ( ) _ _ in on pfm tr max reset min out vt n tv = (10.5) to avoid continuous conduction the turns ratio must be high enough so that t reset does not exceed t period C t on C t dead . t period is given by the pwm switching frequency of 40 khz. t reset_max is given by: __ reset max period on max dead t tt t =?? (10.6) thus, the minimum turns ratio is given by: ( ) _ _ in on max tr min reset max out vt n tv = (10.7) (v in t on ) pfm is limited by the iw1692 to be 185 v?s, and t reset_min is required by the ic to be 2.3 s. _ 185 s 15 2.3 s 5.5 tr max v n v ?m = = m the product of v in and t on is typically chosen by equation 10.8 for cc limit performance. for this example we choose 750 v?s. ( ) 700 850 s in on max vs v t v ?m < < ?m (10.8) assuming v indc_min is 77.0 v, then ( ) max (max) (min) (max) 750 s = 9.7 s 77 in on on indc on vt t v v t v ? = ?m = m (10.9) t dead is estimated to be about 4.8 ms, solving for the minimum turns ratio yields. _ _ 25 s 9.7 s 4.8 s 10.5 s reset max reset max t t = m? m? m = m ( ) _ 750 sec 13 10.5 sec 5.5 tr min v n v ?m = = m pick a number between the maximum and minimum turns ratio; in the example the turn ratio is 13. a turns ratio in the range of 11 to 15 is suggested for optimal performance. 10.5 input bulk capacitor the input bulk capacitance (c1 // c2) is chosen to maintain enough input power to sustain constant output power even as the input voltage is dropping. in order for this to be true the minimum total input bulk capacitance must be: (min) (min) 1 2 2 22 (min) (min) power supply power supply 2 0.25 arcsin 2 assume 72% 5.5 1 7.333 72% indc inac v in v bulk inac indc line out out in in p c vv f vi p va pw ?? ?? + ?? ?? ?? ?? = ?? ? ?? = h h= = = (10.10) from this result we can now get v indc_min with 77.0 v into equation 10.10. ( ) ( ) 77 1 2 2 85 22 2 7.333 0.25 arcsin 13.26 f 2 85 77 47 v vac w hz ?? + ?? ?? = m ? increase the value of c1 // c2 to account for effciency losses. for this example, 13.6 f is chosen. 10.6 current sense resistor the i sense resistor determines the maximum current output of the power supply. the output current of the power supply is determined by: 1 _ 2 reset out tr pri pk x period t i ni t = h (10.11) x is the transformer conversion effciency. when the maximum current output is achieved the voltage seen on the i sense pin (v isense ) should reach its maximum. thus, at constant current limit: iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 11 f ebr ua r y 13, 2012 _ _ isense cc pri pk isense v i r = (10.12) substituting this into equation 10.11 gives: () 2 out isense period isense cc tr x reset ir t v nt = h (10.13) during constant current mode, where output current is at its maximum, the frst term in equation 10.13 is constant. therefore, we can call this k c . substituting this back into equation 10.13 we get: _ period isense cc c reset t vk t = (10.14) for iw1692 k c is 0.264 v, therefore r isense depends on the maximum output current by: 2 tr c isense x out nk r i = h (10.15) using this equation and n tr from section 10.4 assume x is 87%: 13 0.264 87% 1.5 21 isense v r a = =w we recommend using 1% tolerance resistors for r isense . 10.7 magenitizing inductance a feature of the iw1692 is the lack of dependence on the magnetizing inductance for the cc curve. although the constant current limit does not depend on the magnetizing inductance, there are still restrictions on the magnetizing inductance. the maximum l m is limited by the amount of power that needs to come out of the transformer in order for the power supply to regulate. this is given by: ( ) 2 ' max _ _ _ 40 2 in on m max xfmr max out out xfmr max x v t khz l p vi p ? = = h (10.16) the minimum l m is limited by the maximum allowable primary peak current (i pri_pk ). 0.9 v on the i sense pin should correspond to the maximum allowable primary peak current. therefore, the maximum primary peak current is: _ 0.9 pri pk isense v i r < (10.17) thus, l m is limited by: ( ) _ 0.9 in on max m min isense vt l vr ? = (10.18) there is also a lower limit on i sense signal of 0.2 v. this gives a second maximum value on l m ; compare this with the value obtained from equation 10.16 and pick the smaller of the two values. ( ) 2 _ _ 2 2 0.2 40 xfmr max isense m max pr l v khz = (10.19) we can obtain the amount of power that needs to come out of the transformer as: _ 5.5 1 6.332 87% xfmr max va pw = = substituting this into equation 10.16 we get: ( ) 2 ' _ 750 s 40 1.78 2 6.322 m max v khz l mh w ?m = = to get the minimum value of the primary inductance, use the value for r isense from section 10.6. _ 0.9 .6 1.5 pri pk v ia <= w substituting this primary peak current into equation 10.18: _ 750 sec 1.25 0.9 1.5 m min v l mh v ?m = = w choose a primary inductance somewhere between 1.78 mh and 1.42 mh; we chose 1.5 mh. 10.8 primary winding in order to keep the transformer from saturation, the maximum fux density must not be exceeded. therefore the minimum primary winding on the transformer must meet: ( ) in on max pri max e vt n ba ? (10.19) where: b max is maximum fux density and a e is the cross- sectional area of the core. iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 12 f ebr ua r y 13, 2012 picking (v in t on ) max to be 750 v?sec and getting the maximum fux density and core area from the transformer datasheet, we can calculate the minimum number of turns for the primary winding. substitute b max as 320mt and the area of the core to be 19.2 mm 2 we solve equation 10.19 to get: 2 750 s 122.1 320 19.2 pri v n turns mt mm ?m = to avoid hitting the maximum fux density, pick a value for n pri to be higher than this. in this example 144 turns is picked. 10.9 secondary winding from the primary winding turns, we obtain the secondary winding. . pri sec tr n n n = (10.20) thus, in our example: 144 11 13 sec n turns = = at this point it is advantageous to make sure the primary winding and secondary winding chosen is actually feasible to wind. 10.10 bias winding v cc is the supply to the iw1692 and should be between 12 v and 16 v. the number of auxiliary windings needs to ensure that v cc does not exceed 16 v. ( ) sec cc fd bias out n vv n v + = (10.21) the number of auxiliary windings can be calculated using equation 10.21. let v cc = 12 v 11 12.5 25 5.5 bias turns v n turns v = = here weve actually chosen a lower number for the bias winding, 22 turns. 10.11 vsense resistors and winding the output voltage regulation is mainly determined by the feedback signal v sense . _ sense out pcb sense vv k = (10.22) where: 4 43 vsense sense sec n r k rr n = + (10.23) internally, v sense is compared to a reference voltage 1.538 v. from equation 10.22 we get: 1.538 0.3076 5.0 sense v k v = = (10.24) (5.0 v without the addition of v fd is used here see 9.3 for details) solving for r4 in equation 10.23 assuming r3 is 20 k, and n vsense is 24 turns we get r4 should be around 3 k. in fgure 12.0.1, c8 is used to help flter the v sense signal. 10.12 output capacitors assuming an ideal capacitor where esr (equivalent series resistance) and esl (equivalent series inductance) are negligible then: __ out out out ripple pk q c v = (10.25) the output capacitor supplies the load current when the secondary current is below the output current. ( ) 2 _ 2 2 m sec pk out out tr x out li i q nv ? = h (10.26) the secondary peak current is: ( ) in on max sec tr x m vt in l ? = h (10.27) assuming we want to get under 50 mv of ripple on the output: ( ) 2 2 720 s 13 87% 5.655 1.5 1.5 5.655 1 20 c 2 13 87% 5.5 20 c c 402 f 50 sec out out v ia mh mh a a q v mv ?m = = ? = = m m = = m in this calculations esr and esl are ignored; the reason this calculation is still valid is because of the second stage lc flter, l3 and c11. these two components reduce the esr iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 13 f ebr ua r y 13, 2012 and esl ripple. however, the actual output capacitance needs to be higher than this calculated value. 10.13 snubber network the snubber network is implemented to reduce the voltage stress on the mosfet immediately following the turn off of the gate drive. the goal is to dissipate the energy from the leakage inductance of the transformer. for simplicity and a more conservative design frst assume the energy of the leakage inductance is only dissipated through the snubber. thus: 2 22 11 _3 22 lk pri pk pk val li c v v ?? = ? ?? (10.28) l lk can be measured from the transformer, i pri_pk is 0.9 v divided by r isense , and v pk is the peak v ds of the mosfet. choose c3, keeping in mind that the larger the value of c3 you choose, the lower the voltage stress is that is applied to the mosfet. however, capacitors are more expensive the larger their capacitance. choose c3 based on these two criteria and select v pk and v val . now a resistor needs to be selected to dissipate v pk to v val during the on-time of the gate driver. the dissipation of this resistor is given by: 53 tperiod rc val pk v e v ? ? = (10.29) using equation 10.29 solve for r5. this will give a conservative estimate of what c3 and r5 should be. included in the snubber network is also a resistor (r6) in series with the diode (d6). d6 directs the current to c3 when the mosfet is turned off; however there is some reverse current that goes through the diode immediately after the mosfet is turned back on. this reverse current occurs because there is a short period of time when the diode still conducts after switching from forward biased to reverse biased. this conduction will distort the falling edge of the v sense curve and affect the operation of the ic. so, the resistor, r6, is there to diminish the reverse current that goes through d6 immediately after the mosfet is turned on. 10.14 on-time delay filter iw1692 also contains a feature that allows for adjustment to match high line and low line constant current curves. the mismatch in high line and low line curves is due to the ic propagation delay, and the mosfet turn off delay. iw1692 slightly over compensates for them to provide fexibility in design by providing extra delay. r15 and c5 can be used to adjust the compensation. to determine values r15 and c5 follow these steps: 1. measure the difference between high line and low line constant current limit without r15 and c5. 2. find the curve that best matches this difference from figure 11.0.7. 3. find the l m that matches the power supply. match the t rc . 4. find r15 and c5 from equation 10.30: 15 5 rc rc t= (10.30) we observe that the difference between high line and low line constant current limit is 20 ma. matching the primary inductance 2 mh and the curve, we fnd t rc to be 4.410 -8 s. we then pick r15 to be 1 k and substitute into equation 10.30. 8 5 4.4 10 sec 1 kc ? ? = w solving for c5, we get 44 pf. the result should be a match between high line and low line constant current curves. see fgure 11.0.7 for details. 10.15 pcb layout in the iw1692, there are two signals that are important to control output performance; these are the i sense signal and the v sense signal. the i ss resistor should be close to the source of the mosfet to avoid any trace resistance from contaminating the i sense signal. also the i sense signal should be placed close to the i sense pin. the v sense signal should be placed close to the transformer to improve the quality of the sensing signal. iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 14 f ebr ua r y 13, 2012 iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 15 f ebr ua r y 13, 2012 figure 11.0.1 v sense effciency at 90 v ac and 264 v ac figure 11.0.2 regulation figure 11.0.4 v sense short before start-up (no load) 11.0 design example performance characteristics figure 11.0.5 i sense short at 90 v ac figure 11.0.6 output short fault (50% load) iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 16 f ebr ua r y 13, 2012 12.0 application circuit n rtn l t1-b t1-a 5v/1a q1 d1 - d4 in4007 + + + + u1 iw1692 4 2 6 5 3 1 r1 4.7 k ? r11 2.2 m ? r16 100 ? r9 100 ? r15 1 k ? r13 56 k ? r18 1.5 ? r10 2.43 m ? l1 1 mh l3 1h r14 560 ? r5 100 k ? f1 10 ? r6 150 ? r12 1 ? r3 20k ? r4 3.0 k ? c1 6.8 f/400 v c2 6.8 f/400 v d5 fr102 d6 z1 15v c3 1 nf/500 v c10 650 f /10 v c11 330 f/10v c5 47 pf c6 470 pf c7 470 nf c8 68 pf c9 4.7f output gnd i sense v in v cc v sense figure 12.0.1. typical application circuit figure 11.0.7. t on compensation chart 11.0 design example performance characteristics 180 150 120 90 60 30 0 ( r dly x c dly ), rc (ns) magnetizing inductance l m (mh) 0 0.75 1.50 2.25 3.0 50 ma 40 ma 30 ma 20 ma 10 ma iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 17 f ebr ua r y 13, 2012 13.0 physical dimensions figure 13.0.1. physical dimensions, 6-lead sot-23 package 14.0 ordering information 1 3 4 6 5 2 6-lead small outline transistor package d compliant to jedec standard mo-178ab controlling dimensions are in millimeters this package is rohs compliant and halide free. soldering temperature resistance: [a] package is ipc/jedec std 020d moisture sensitivity level 1 [b] package exceeds jedec std no. 22-a111 for solder immersion resistance; packages can withstand 10 s immersion < 270oc dimension d does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.25 mm per side. the package top may be smaller than the package bottom. dimensions d and e1 are are determined at the outermost extremes of the plastic body exclusive of mold flash, tie bar burrs and interlead flash, but including any mismatch between top and bottom of the plastic body. seating plane a1 coplanarity 0.10 e1 b e e1 a a2 c l symbol millimeters a1 min max 0.00 0.15 a - 1.45 b 0.30 0.50 c 0.08 0.22 d 2.80 3.00 e e1 e 0.95 bsc e1 1.90 bsc 2.80 bsc 1.60 bsc l 0.30 0.60 0 8 a2 0.90 1.30 e 2.90 bsc part number mark package description IW1692-00 gxxx sot23-6l tape & reel 1 note 1: tape & reel quantity for sot23 is 3,000/reel. iw1692 low-power off-line digital pwm controller not recommended for new designs
r ev . 2.0 iw1692 p age 18 f ebr ua r y 13, 2012 iwatt inc. is a fabless semiconductor company that develops intelligent power management ics for computer, communication, and consumer markets. the companys patented pulsetrain ? technology, the industrys frst truly digital approach to power system regulation, is revolutionizing power supply design. trademark information ? 2012 iwatt, inc. all rights reserved. iwatt, ez-emi, and pulsetrain are trademarks of iwatt, inc. all other trademarks and registered trademarks are the property of their respective companies. contact information web: https://www.iwatt.com e-mail: info@iwatt.com phone: 408-374-4200 fax: 408-341-0455 iwatt inc. 675 campbell technology parkway, suite 150 campbell, ca 95008 disclaimer iwatt reserves the right to make changes to its products and to discontinue products without notice. the applications information, schematic diagrams, and other reference information included herein is provided as a design aid only and are therefore provided as-is. iwatt makes no warranties with respect to this information and disclaims any implied warranties of merchantability or non-infringement of third-party intellectual property rights. iwatt cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an iwatt product. no circuit patent licenses are implied. certain applications using semiconductor products may involve potential risks of death, personal injury, or severe property or environmental damage (critical applications). iwatt semiconductor products are not designed, intended, authorized, or warranted to be suitable for use in life - support applications, devices or systems, or other critical applications. inclusion of iwatt products in critical applications is understood to be fully at the risk of the customer. questions concerning potential risk applications should be directed to iwatt, inc. iwatt semiconductors are typically used in power supplies in which high voltages are present during operation. high-voltage safety precautions should be observed in design and operation to minimize the chance of injury . about iwatt iw1692 low-power off-line digital pwm controller not recommended for new designs

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