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r ev . 1.2 i w1698 p age 1 f ebr ua r y 6, 2012 1.0 features primary-side feedback eliminates opto-isolators and simplifes design no-load power consumption < 30 mw at 230 v ac with typical application circuit (5 star rating) adaptive multi-mode pwm/pfm control improves effciency quasi-resonant operation for highest overall effciency ez-emi ? design to easily meet global emi standards direct drive of low-cost bjt switch dynamic base current control very tight constant voltage and constant current regulation with primary-side-only feedback no external compensation components required complies with epa 2.0 energy-effciency specifcations with ample margin low start-up current (8 a typical) built-in soft start built-in short circuit protection and output overvoltage protection built-in current sense resistor short circuit protection no audible noise over entire operating range figure 3.1: IW1698 typical application circuit (achieving < 30 mw no-load power consumption) 2.0 description the IW1698 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 IW1698 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 IW1698 can achieve both highest average effciency and less than 30 mw no-load power consumption with typical application circuit. 3.0 applications low power ac/dc adapter/chargers for cell phones, pdas, digital still cameras linear ac/dc replacement l + v out gnd u1 IW1698 v cc gnd v sense output i sense 1 3 2 5 4 n + IW1698 low-power off-line digital green-mode pwm controller
r ev . 1.2 i w1698 p age 2 f ebr ua r y 6, 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. IW1698 v cc gnd v sense output i sense 1 2 3 5 4 5.0 absolute maximum ratings 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 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 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 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 IW1698 low-power off-line digital green-mode pwm controller
r ev . 1.2 i w1698 p age 3 f ebr ua r y 6, 2012 6.0 electrical characteristics v cc = 12 v, -40c t a +85c 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 1.538 v output ovp threshold -00 v sense(max) t a =25c, negative edge 1.834 v output ovp threshol -05 v sense(max) t a =25c, negative edge load = 100 % 1.880 v i sense section (pin 4) overcurrent threshold v ocp 1.1 1.15 v i sense regulation upper limit (note 1) v ipk(high) 1.0 v i sense regulation lower limit (note 1) v ipk(low) 0.25 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 3 6 w switching frequency (note 2) f sw > 50% load 40 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 9.5 10.5 11.5 v undervoltage lockout threshold v cc(uvl) v cc falling 3.9 4.1 4.3 v start-up current i in(st) v cc = 10 v 8 15 a quiescent current i ccq no i b current 2.5 3.5 ma zener breakdown voltage v zb zener current = 1 ma t a =25c 18 19 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. 1.523 1.553 IW1698 low-power off-line digital green-mode pwm controller
r ev . 1.2 i w1698 p age 4 f ebr ua r y 6, 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 10.20 -50 -25 10.30 10.40 10.50 10.60 10.70 0 25 50 75 100 125 150 v cc start-up threshold (v) ambient temperature (oc) 34 -50 -25 36 38 40 42 44 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) 4.94 -50 -25 4.96 4.98 4.00 4.02 4.04 0 25 50 75 100 125 150 v cc uvlo (v) ambient temperature (oc) 0.0 0.0 2.0 4.0 6.0 8.0 10.0 3.5 7.0 10.5 14.0 v cc (v) v cc supply start-up current (a) figure 7.5 : v cc vs. v cc supply start-up current notes: note 1. operating frequency varies based on the load conditions, see section 9.6 for more details. IW1698 low-power off-line digital green-mode pwm controller
r ev . 1.2 i w1698 p age 5 f ebr ua r y 6, 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 1.1 v b j t b a s e d r i v e e nable 3 ocp = 1.538 v v cc v fb v sense(nom) v sense i sense v ipk i pk figure 8.1: IW1698 functional block diagram 9.0 theory of operation the IW1698 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 IW1698 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 IW1698 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 protection features include overvoltage protection (ovp), output short circuit protection (scp), over current protection (ocp), single point 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. IW1698 low-power off-line digital green-mode pwm controller
r ev . 1.2 i w1698 p age 6 f ebr ua r y 6, 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 10.5 v (typical) and will shut-down when the v cc voltage is 4.0 v (typical). a decoupling capacitor 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 start-up prior to start-up, the v cc pin is charged typically through start- up 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 IW1698 commences soft start function. an adaptive soft-start control algorithm is applied at startup state, during which the initial output pulses will be small and gradually get larger until the full pulse width is achieved. the peak current is limited cycle by cycle by the i peak comparator. if at any time the v cc voltage drops below v cc(uvl) threshold then all the digital logic is reset. at this time enable signal becomes low and the v cc capacitor is charged up again towards the start-up threshold. 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 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: IW1698 low-power off-line digital green-mode pwm controller
r ev . 1.2 i w1698 p age 7 f ebr ua r y 6, 2012 ( ) ( ) _ 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 IW1698, v can be ignored. the real-time waveform analyzer in the IW1698 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 IW1698 shuts down. 9.5 constant current operation the constant current (cc mode) is useful in battery charging applications. during this mode of operation the IW1698 will regulate the output current at a constant level regardless of the output voltage, while avoiding continuous conduction mode. to achieve this regulation the IW1698 senses the load current indirectly through the primary current. the primary current is detected by the i sense pin through a resistor from the bjt emitter to ground. output voltage output current i out(cc) v nom cv mode cc mode figure 9.4: power envelope IW1698 low-power off-line digital green-mode pwm controller
r ev . 1.2 i w1698 p age 8 f ebr ua r y 6, 2012 9.6 multi-mode pwm/pfm control and quasi-resonant switching the IW1698 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 IW1698 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. as the load current is further reduced, the IW1698 transitions to a deep pfm mode (dpfm) which reduces the switching frequency to a very low level. while operating in the adaptive multi-mode pwm/pfm control, IW1698 also incorporates a unique quasi-resonant switching in both cv and cc operations. together these innovative digital control architecture and algorithms enable IW1698 to achieve highest overall effciency and lowest emi. 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 IW1698 shuts off. 9.8 internal loop compensation the IW1698 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 IW1698. when the v sense signal exceeds the output ovp threshold at point 1 indicated in fgure 9.3 the IW1698 shuts down. the IW1698 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 IW1698 detects that the minimum v in is reached, and shuts down. the maximum t on limit is set to 22 s. also, the IW1698 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 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 IW1698. with the i sense pin the IW1698 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 1.1 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 IW1698 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 IW1698 is that it directly drives a bjt switching device with dynamic base current control to optimize performance. the bjt base current ranges from 10 ma to 31 ma, and is dynamically controlled according to the power supply load change. the higher the output power, IW1698 low-power off-line digital green-mode pwm controller
r ev . 1.2 i w1698 p age 9 f ebr ua r y 6, 2012 the higher the base current. specifcally, the base current is related to v ipk , as shown in figure 9.5. 0 5 10 15 20 25 30 35 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) figure 9.5: base drive current vs. v ipk 9.12 cable drop compensation the IW1698 incorporates an innovative method to compensate for any ir drop in the secondary circuitry including cable and cable connector. a 2.5 w adapter with 5 v dc output has 3% deviation at 0.5 a load current due to the drop across a 24 awg, 1.8 meter dc cable without cable compensation. the IW1698 compensates for this voltage drop by providing a voltage offset to the feedback signal based on the amount of load current detected. to calculate the amount of cable compensation needed, take the resistance of the cable and connector and multiply by the maximum output current. IW1698 low-power off-line digital green-mode pwm controller
r ev . 1.2 i w1698 p age 10 f ebr ua r y 6, 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 IW1698-00 cable comp = 0 mv sot-23 tape & reel 1 IW1698-05 cable comp = 150 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 IW1698 low-power off-line digital green-mode pwm controller
r ev . 1.2 i w1698 p age 11 f ebr ua r y 6, 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: http://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 IW1698 low-power off-line digital green-mode pwm controller

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