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r ev . 1.1 i w1706 p age 1 f ebr ua r y 1, 2012 1.0 features primary-side feedback eliminates opto-isolators and simplifes design adaptively controlled soft start-up enables fast and smooth start-up for a wide range of capacitive loads (from 330 f to 6000 f) very tight constant voltage regulation ez-emi ? design enhances manufacturability intrinsically low common mode noise optimized 72 khz maximum pwm switching frequency achieves best size and effciency adaptive multi-mode pwm/pfm control improves effciency quasi-resonant operation for highest overall effciency direct drive of low-cost bjt switch dynamic base current control no external compensation components required complies with epa 2.0 energy-effciency specifcations with ample margin built-in short circuit protection and output overvoltage protection built-in current sense resistor short circuit protection constant current control enables output current limit and overload protection no audible noise over entire operating range figure 3.1: IW1706 typical application circuit 2.0 description the IW1706 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 directly drives a power bjt and operates in quasi-resonant mode to provide high effciency along with a number of key built-in protection features while minimizing the external component count, simplifying emi design and lowering the total bill of material cost. the IW1706 features a distinctive soft-start scheme, which allows for fast and yet smooth start-up with both small and large capacitive loads. the IW1706 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. iwatts innovative proprietary technology ensures that power supplies built with the IW1706 can achieve both highest average effciency and fast yet smooth start-up with a wide range of capacitive loads, and are ideal for network power adapter applications. 3.0 applications network power adapters for adsl, wireless access points, routers. l + v out gnd u1 IW1706 v cc gnd v sense output i sense 1 3 2 5 4 n + IW1706 low-power off-line digital green-mode pwm controller
r ev . 1.1 i w1706 p age 2 f ebr ua r y 1, 2012 4.0 pinout description pin # name type pin description 1 v cc power input power supply for control logic. 2 gnd ground ground. 3 v sense analog input auxiliary voltage sense (used for primary regulation). 4 i sense analog input primary current sense. used for cycle-by-cycle peak current control and limit. 5 output output base drive for bjt. IW1706 v cc gnd v sense output i sense 1 2 3 5 4 absolute maximum ratings are the parameter values or ranges which can cause permanent damage if exceeded. for maximum safe operating conditions, refer to electrical characteristics in section 6.0. parameter symbol value units dc supply voltage range (pin 1, i cc = 20ma max) v cc -0.3 to 18.0 v continuous dc supply current at v cc pin (v cc = 15 v) i cc 20 ma output (pin 5) -0.3 to 4.0 v v sense input (pin 3, i vsense 10 ma) -0.7 to 4.0 v i sense input (pin 4) -0.3 to 4.0 v maximum junction temperature t j max 150 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 190 c/w esd rating per jedec jesd22-a114 2,000 v latch-up test per jedec 78 100 ma figure 4.1: 5 lead sot-23 package 5.0 absolute maximum ratings IW1706 low-power off-line digital green-mode pwm controller
r ev . 1.1 i w1706 p age 3 f ebr ua r y 1, 2012 6.0 electrical characteristics v cc = 12 v, -40c t a +85c, unless otherwise specifed. parameter symbol test conditions min typ max unit v sense section (pin 3) input leakage current i bvs v sense = 2 v 1 a nominal voltage threshold v sense(nom) t a =25c, negative edge 1.518 1.533 1.548 v output ovp threshold -00 (note 1) v sense(max) t a =25c, negative edge 1.834 v output ovp threshold -01 (note 1) v sense(max) t a =25c, negative edge load = 100 % 1.855 v output ovp threshold -03 (note 1) v sense(max) t a =25c, negative edge load = 100% 1.901 v i sense section (pin 4) overcurrent threshold v ocp 1.11 1.15 1.19 v i sense regulation upper limit (note 1) v ipk(high) 1.0 v i sense regulation lower limit (note 1) v ipk(low) 0.23 v input leakage current i lk i sense = 1.0 v 1 a output section (pin 5) output low level on-resistance r ds(on)lo i sink = 5 ma 1 3 w switching frequency (note 2) f sw > 50% load 72 khz v cc section (pin 1) maximum operating voltage (note 1) v cc(max) 16 v start-up threshold v cc(st) v cc rising 10.0 11.0 12.0 v undervoltage lockout threshold v cc(uvl) v cc falling 3.8 4.0 4.2 v start-up current i in(st) v cc = 10 v 1.0 1.7 3.0 a quiescent current i ccq no i b current 2.7 4.0 ma zener breakdown voltage v zb zener current = 5 ma t a =25c 18.5 19.5 20.5 v notes: note 1. these parameters are not 100% tested, guaranteed by design and characterization. note 2. operating frequency varies based on the load conditions, see section 9.6 for more details. IW1706 low-power off-line digital green-mode pwm controller
r ev . 1.1 i w1706 p age 4 f ebr ua r y 1, 2012 7.0 typical performance characteristics figure 7.1: v cc uvlo vs. temperature figure 7.2: start-up threshold vs. temperature figure 7.3: switching frequency vs. temperature 1 figure 7.4: internal reference vs. temperature 10.0 -50 -25 10.4 10.8 11.2 11.6 12.0 0 25 50 75 100 125 150 v cc start-up threshold (v) ambient temperature (oc) 60 -50 -25 64 68 72 76 80 0 25 50 75 100 125 150 f sw @ load > 50% (khz) ambient temperature (oc) 1.990 -50 -25 1.994 1.998 2.002 2.006 2.010 0 25 50 75 100 125 150 internal reference voltage (v) ambient temperature (oc) 3.88 -50 -25 3.92 3.96 4.00 4.04 4.08 0 25 50 75 100 125 150 v cc uvlo (v) ambient temperature (oc) 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 6.0 9.0 12.0 v cc (v) v cc supply start-up current (a) figure 7.5: v cc vs. v cc supply start-up current otes: note 1. operating frequency varies based on the load conditions, see section 9.6 for more details. IW1706 low-power off-line digital green-mode pwm controller
r ev . 1.1 i w1706 p age 5 f ebr ua r y 1, 2012 8.0 functional block diagram 1 5 2 4 g n d o u t p u t s t a r t-up d i g i t a l l o g i c c o n t r o l s i g n a l c o n d i t i o n i n g d a c 1.15 v b j t b a s e d r i v e e nable 3 ocp = 1.533 v v cc v fb v sense(nom) v sense i sense v ipk i pk figure 8.1: IW1706 functional block diagram 9.0 theory of operation the IW1706 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 higher power levels 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 8.1, the digital logic control block generates the switching on-time and off-time information based on the output voltage and current feedback signal and provides commands to dynamically control the external bjt base current. the system loop is automatically compensated internally by a digital error amplifer. adequate system phase margin and gain margin are guaranteed by design and no external analog components are required for loop compensation. the IW1706 uses an advanced digital control algorithm to reduce system design time and increase reliability. furthermore, accurate secondary constant-current operation is achieved without the need for any secondary-side sense and control circuits. the IW1706 uses adaptive multi-mode pwm/pfm control to dynamically change the bjt switching frequency for effciency, emi, and power consumption optimization. in addition, it achieves unique bjt quasi-resonant switching to further improve effciency and reduce emi. built-in single- point fault protection features include overvoltage protection (ovp), output short circuit protection (scp), over current protection (ocp), and i sense fault detection. in particular, it ensures that power supplies built with the IW1706 are best suited for power adapter applications such as adsl modems that have large capacitive loads. 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. IW1706 low-power off-line digital green-mode pwm controller
r ev . 1.1 i w1706 p age 6 f ebr ua r y 1, 2012 9.1 pin detail pin 1 C v cc power supply for the controller during normal operation. the controller will start up when v cc reaches 11.0 v (typical) and will shut-down when the v cc voltage is 4.0 v (typical). a decoupling capacitor of 0.1 f or so should be connected between the v cc pin and gnd. pin 2 C gnd ground. pin 3 C v sense sense signal input from auxiliary winding. this provides the secondary voltage feedback used for output regulation. pin 4 C i sense primary current sense. used for cycle-by-cycle peak current control and limit. pin 5 C output base drive for the external power bjt switch. 9.2 adaptively controlled soft start-up the IW1706 features an innovative proprietary soft-start scheme to achieve fast yet smooth start-up with a wide range of output loads, including capacitive loads typically from 330 f to 6000 f, and for output voltage covering typically from 5v to 12v. prior to the start-up, the v cc pin is charged through startup resistors. when v cc bypass capacitor is fully charged to a voltage higher than the start- up threshold v cc(st) , the enable signal becomes active to enable the control logic, and the IW1706 commences the soft-start function. during the soft-start process, the primary-side peak current is limited cycle by cycle by the i peak comparator. the whole soft-start process can break down into several stages based on the output voltage levels, which is indirectly sensed by v sense signal at the primary side. at different stages, the IW1706 adaptively controls the switching frequency and primary-side peak current such that the output voltage can always build up very fast at the early stages and smoothly transition to the desired regulation voltage at the fnal stage, regardless of any capacitive and resistive loads that the applications may incur. with a lowest system cost, this adaptively controlled soft start-up feature makes the IW1706 ideal in network power adapter applications such as adsl modems that have large capacitive loads. if at any time the vcc voltage drops below the undervoltage lockout (uvlo) threshold v cc(uvl) then the IW1706 goes to shutdown. at this time enable signal becomes low and the v cc capacitor begins to charge up again towards the start- up threshold to initiate a new soft-start process. v cc v cc(st) enable start-up sequencing figure 9.1: start-up sequencing diagram 9.3 understanding primary feedback figure 9.2 illustrates a simplifed fyback converter. when the switch q1 conducts during t on (t), the current i g (t) is directly drawn from rectifed sinusoid v g (t). the energy e g (t) is stored in the magnetizing inductance l m . 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 d1 q1 n:1 v aux c o v g (t) i g (t) + ? i in (t) i d (t) figure 9.2: simplifed flyback converter in order to tightly regulate the output voltage, the information about the output voltage and load current need to be accurately sensed. in the dcm fyback converter, this information can be read via the auxiliary winding or IW1706 low-power off-line digital green-mode pwm controller
r ev . 1.1 i w1706 p age 7 f ebr ua r y 1, 2012 the primary magnetizing inductance (l m ). during the q1 on-time, the load current is supplied from the output flter capacitor c o . the voltage across l m is v g (t), assuming the voltage dropped across q1 is zero. the current in q1 ramps up linearly at a rate of: ( ) ( ) gg m di t v t dt l = (9.1) at the end of on-time, the current has ramped up to: ( ) ( ) _ g on g peak m vt t it l = (9.2) this current represents a stored energy of: ( ) 2 _ 2 m g g peak l e it = (9.3) when q1, turns off at t o , 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 t o , the primary current transfers to the secondary at a peak amplitude of: ( ) ( ) _ p d g peak s n it i t n = (9.4) assuming the secondary winding is master, and the auxiliary winding is slave, v aux 0v v aux = -v in x n aux n p v aux = v o x n aux n s 1 2 figure 9.3: auxiliary voltage waveforms the auxiliary voltage is given by: ( ) v aux aux o s n vv n = +? (9.5) and refects the output voltage as shown in figure 9.3. the voltage at the load differs from the secondary voltage by a diode drop and 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 will be a fxed v. furthermore, if the voltage can be read when the secondary current is small, v will also be small. with the IW1706, v can be ignored. the real-time waveform analyzer in the IW1706 reads this information cycle by cycle. the part then generates a feedback voltage v fb . the v fb signal precisely represents the output voltage under most conditions and is used to regulate the output voltage. 9.4 constant voltage operation after soft-start has been completed, the digital control block measures the output conditions. it determines output power levels and adjusts the control system according to a light load or heavy load. if this is in the normal range, the device operates in the constant voltage (cv) mode, and changes the pulse width (t on ) and off time (t off ) in order to meet the output voltage regulation requirements. if no voltage is detected on v sense it is assumed that the auxiliary winding of the transformer is either open or shorted and the IW1706 shuts down. 9.5 current limit and constant current operation at overload condition, the IW1706 enters constant current (cc) mode to limit the output current on cycle-by-cycle basis. during this mode of operation the output current is limited to a constant level regardless of the output voltage, while avoiding continuous conduction mode operation. in case of very heavy loading, when the output voltage is low enough, the IW1706 shuts down. the IW1706 senses the load current indirectly through the primary current, which is detected by the pin i sense through a resistor from the bjt emitter to ground. IW1706 low-power off-line digital green-mode pwm controller
r ev . 1.1 i w1706 p age 8 f ebr ua r y 1, 2012 output voltage output current i out(cc) v nom cv mode cc mode figure 9.4: power envelope 9.6 multi-mode pwm/pfm control and quasi-resonant switching the IW1706 uses a proprietary adaptive multi-mode pwm/pfm control to dramatically improve the light-load effciency and thus the overall average effciency. during the constant voltage (cv) operation, the IW1706 normally operates in a pulse-width-modulation (pwm) mode during heavy load conditions. in the pwm mode, the switching frequency keeps around constant. as the output load i out is reduced, the on-time t on is decreased, and the controller adaptively transitions to a pulse-frequency- modulation (pfm) mode. during the pfm mode, the bjt is turned on for a set duration under a given instantaneous rectifed ac input voltage, but its off time is modulated by the load current. with a decreasing load current, the off time increases and thus the switching frequency decreases. when the switching frequency approaches to human ear audio band, the IW1706 transitions to a second level of pwm mode, namely deep pwm mode (dpwm). during the dpwm mode, the switching frequency keeps around 25 khz in order to avoid audible noise. as the load current is further reduced, the IW1706 transitions to a second level of pfm mode, namely deep pfm mode (dpfm), which can reduce the switching frequency to a very low level. although the switching frequency drops across the audible frequency range during the dpfm mode, the current in the power converter has reduced to an insignifcant level in the dpwm mode before transitioning to the dpfm mode. therefore, the power converter practically produces no audible noise, while achieving high effciency across varying load conditions. the IW1706 also incorporates a unique proprietary quasi- resonant switching scheme that achieves valley-mode turn on for every pwm/pfm switching cycle, during all pfm and pwm modes, and in both cv and cc operations. this unique feature greatly reduces the switching loss and dv/dt across the entire operating range of the power supply. due to the nature of quasi-resonant switching, the actual switching frequency can vary slightly cycle by cycle, providing the additional beneft of reducing emi. together these innovative digital control architecture and algorithms enable the IW1706 to achieve highest overall effciency and lowest emi, without causing audible noise over entire operating range. 9.7 variable frequency operation mode at each of the switching cycles, the falling edge of v sense will be checked. if the falling edge of v sense is not detected, the off-time will be extended until the falling edge of v sense is detected. the maximum allowed transformer reset time is 110 s. when the transformer reset time reaches 110 s, the IW1706 shuts off. 9.8 internal loop compensation the IW1706 incorporates an internal digital error amplifer with no requirement for external loop compensation. for a typical power supply design, the loop stability is guaranteed to provide at least 45 degrees of phase margin and -20 db of gain margin. 9.9 voltage protection features the secondary maximum output dc voltage is limited by the IW1706. when the v sense signal exceeds the output ovp threshold at point 1 indicated in figure 9.3 the IW1706 shuts down. the IW1706 protects against input line undervoltage by setting a maximum t on time. since output power is proportional to the squared v in t on product then for a given output power as v in decreases the t on will increase. thus by knowing when the maximum t on time occurs the IW1706 detects that the minimum v in is reached, and shuts down. the maximum t on limit is set to 13.8 s. also, the IW1706 monitors the voltage on the v cc pin and when the voltage on this pin is below uvlo threshold the ic shuts down immediately. when any of these faults are met the ic remains biased to discharge the v cc supply. once v cc drops below uvlo threshold, the controller resets itself and then initiates a new IW1706 low-power off-line digital green-mode pwm controller
r ev . 1.1 i w1706 p age 9 f ebr ua r y 1, 2012 soft-start cycle. the controller continues attempting start-up until the fault condition is removed. 9.10 pcl, ocp and srs protection peak-current limit (pcl), over-current protection (ocp) and sense-resistor short protection (srsp) are features built-in to the IW1706. with the i sense pin the IW1706 is able to monitor the peak primary current. this allows for cycle by cycle peak current control and limit. when the primary peak current multiplied by the i sense resistor is greater than 1.15 v over current (ocp) is detected and the ic will immediately turn off the base driver until the next cycle. the output driver will send out a switching pulse in the next cycle, and the switching pulse will continue if the ocp threshold is not reached; or, the switching pulse will turn off again if the ocp threshold is reached. if the ocp occurs for several consecutive switching cycles, the IW1706 shuts down. if the i sense resistor is shorted there is a potential danger of the over current condition not being detected. thus, the ic is designed to detect this sense-resistor-short fault after startup and shut down immediately. the v cc will be discharged since the ic remains biased. once v cc drops below the uvlo threshold, the controller resets itself and then initiates a new soft-start cycle. the controller continues attempting to startup, but does not fully startup until the fault condition is removed. 9.11 dynamic base current control one important feature of the IW1706 is that it directly drives a bjt switching device with dynamic base current control to optimize performance. the bjt base current ranges from 13 ma to 40 ma, and is dynamically controlled according to the power supply load change. the higher the output power, the higher the base current. specifcally, the base current is related to v ipk , as shown in figure 9.5. 0 10 20 30 40 base drive current (ma) 0.1 0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 v ipk (v) 50 figure 9.5: base drive current vs. v ipk 9.12 cable drop compensation the IW1706 incorporates an innovative method to compensate for any ir drop in the secondary circuitry including cable and cable connector. a 6-w adapter with 12 v dc output has 1.26% deviation at 0.5 a load current due to the drop across a 24 awg, 1.8 meter dc cable without cable compensation. the IW1706 compensates for this voltage drop by providing a voltage offset to the feedback signal based on the amount of load current detected. the cable comp specifed in the table in section 11.0 refers to the voltage increment at pcb end from no-load to full-load conditions in the cv mode, with the assumption that the secondary diode voltage drop can be ignored at the point when the secondary voltage is sensed. also, the cable comp is specifed based on the nominal output voltage of 5 v. for different output voltage, the actual voltage increment needs to be scaled accordingly. to calculate the amount of cable compensation needed, take the resistance of the cable and connector and multiply by the maximum output current. IW1706 low-power off-line digital green-mode pwm controller
r ev . 1.1 i w1706 p age 10 f ebr ua r y 1, 2012 1 3 4 5 2 5-lead sot package d compliant to jedec standard mo178 controlling dimensions are in millimeters this package is rohs compliant, and conform to halide free limits. 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 @ < 270 c dimension d does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.25 mm per end. dimension e1 does not include interlead flash or protrusion. interlead flash or protrusion shall not exceed 0.25 mm per side. the package top may be smaller than the package bottom. dimension d and e1 are determined at the outermost extremes of the plastic body exclusive of mold flash, tie bar burrs, gate burrs and interlead flash, but including any mismatch between the 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 0.0 0.15 a - 1.45 b 0.30 0.50 c 0.08 0.22 d 2.90 bsc e e1 1.60 bsc e 0.95 bsc e1 1.90 bsc 2.80 bsc l 0.30 0.60 0 8 a2 0.90 1.30 e 10.0 physical dimensions figure 10.1: physical dimensions, 5-lead sot-23 package part number options package description IW1706-00 cable comp = 0 mv sot-23 tape & reel 1 IW1706-01 cable comp = 75 mv sot-23 tape & reel 1 IW1706-03 cable comp = 225 mv sot-23 tape & reel 1 note 1: tape & reel packing quantity is 3,000 per reel. minimum ordering quantity is 3,000. 11.0 ordering information IW1706 low-power off-line digital green-mode pwm controller
r ev . 1.1 i w1706 p age 11 f ebr ua r y 1, 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). iw att 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 IW1706 low-power off-line digital green-mode pwm controller

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