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? 2015 microchip technology inc. ds20005394a-page 1 lr745 features ? accepts inputs from 35 to 450v ? output current limiting ? for pwm ics with start-up threshold voltage of 13.9 - 18.0v ? very low power consumption after start-up applications ? notebook and laptop computers ? telecommunication power supplies ? battery chargers ? motor controllers description lr745 is a high input voltage smps start-up circuit. lr745 is ideally suited for use with industry standard low-voltage, pulse-width modulation (pwm) ics hav- ing start thresholds of 13.9 to 18.0v. it allows the pwm ics to be operated from rectified 120 or 240vac lines, and eliminates the use of power resistors often used for this purpose. the internal circuitry of the lr745 allows the pwm ics to operate at a v cc voltage below their start-threshold voltage after start-up. the auxiliary voltage can be less than the start-threshold voltage, which allows for improved efficiency. current from the high voltage line is drawn only during the start-up period. after start-up, the internal, high-voltage line is disconnected from the ic, thereby reducing the continuous power dissipation to a minimum. high-input voltage smps start-up
lr745 ds20005394a-page 2 ? 2015 microchip technology inc. package type to-92 see table 2-1 for pin information to-243aa (sot-89) vin vout gnd gnd gnd vin vout
? 2015 microchip technology inc. ds20005394a-page 3 lr745 1.0 electrical characteristics absolute maximum ratings input voltage .................................................................................................................. ................................................................ 450v output voltage................................................................................................................. ................................................................. 25v operating and storage temperature .............................................................................................. ............................... -55c to +150c note : stresses above those listed under ?absolut e maximum ratings? may cause permanent dam age to the device. this is a stress rating only and functional operation of the devi ce at those or any other conditions, above those indicated in the operational l istings of this specification, is not implied. ex posure to maximum rating conditions for ext ended periods may affect device reliability. 1.1 electrical specifications table 1-1: electrical characteristics 1 1 test conditions unless otherwise specified: t a = 25c, v in = 450v symbol parameter min typ max units conditions v out output voltage 18.0 24 v i out = 0 v out over temperature 17.7 24.3 v i out = 0, t a = -40c to +85c i out output current limiting 2.0 3.0 4.0 ma v in operating input voltage range 35 450 v i inq input quiescent current 500 a v in = 400v, i out = 0 v off output turn off voltage 12.6 13.25 13.9 v v off over temperature 12.3 13.25 14.2 v t a = -40c to +85c v reset output reset voltage 6.3 7.0 7.7 v v reset over temperature 6.0 7.0 8.0 v t a = -40c to +85c i off v in off-state leakage current 75 a v in = 400v v aux external voltage applied to v out 22 v i aux input current applied to v out 500 a v aux = 22v table 1-2: thermal characteristics package ja to-92 132c/w to-243aa (sot-89) 133c/w
lr745 ds20005394a-page 4 ? 2015 microchip technology inc. 2.0 pin description the locations of the pins are listed in package type . table 2-1: pin description function description vin regulator input. 8 - 450v. gnd ground return for all internal circuitry. this pin must be electrically connected to circuit common. vout regulator output.
? 2015 microchip technology inc. ds20005394a-page 5 lr745 3.0 application information figure 3-1 shows a simplified typical configuration of a switch mode power supply, smps, using lr745 in the start-up circuit. lr745?s vout terminal is connected to the vcc line of a pwm ic. an auxiliary winding on the transformer generates a v cc voltage to power the pwm ic after start-up. lr745 supplies power for the pwm ic only during start-up. after start-up, lr745 turns off and the auxiliary winding supplies power for the pwm ic. figure 3-2 shows the typical curr ent and voltage wave- forms at various stages from power-up to operation powered by the auxiliary winding. 3.1 stage i once a voltage is applied on vin, lr745 starts to charge the v cc capacitor, c 1 . the v cc voltage starts to increase at a rate limited by the internal current limiter of 3.0ma. the pwm ic is in its start-up condition and will typically draw 0.5ma from the v cc line. the v cc voltage will continue to increase until it reaches the pwm ic?s start threshold voltage, typically 16v. 3.2 stage ii once v cc reaches 16v, the pwm ic is in its operating condition and will typically draw 20ma, depending on the operating frequency a nd size of th e switching metal?oxide?semiconductor field-effect transistor (mosfet). the output of lr745, v out , is internally current limited to 3.0ma. the remaining 17ma will be supplied by c 1 , causing the v cc voltage decrease. when v cc decreases to 13.25v, lr745 will turn off its output, thereby reducing its input current from 3.0ma to 10s of microamperes. at this point, all 20ma will be supplied by c 1 . the pwm ic can now operate to a min- imum v cc voltage, typically 10v. once the switching mosfet starts operating, the energy in the primary winding is transferred to the sec- ondary outputs and the auxiliary winding, thereby build- ing up v aux . it is necessary to size the v cc storage capacitor, c 1 , such that v aux increases to a voltage greater than 10v before v cc decreases to 10v. this allows v aux to supply the require d operating current for the pwm ic. if for some reason the auxiliary voltage does not reach 10v, v cc will continue to decrease. once v cc goes below 10v, the pwm ic will return to its start-up condi- tion. the pwm ic will now only draw 0.5ma. v cc will continue to decrease but at a much slower rate. once v cc decreases below 7.0v, lr745 will turn the output, v out , back on. v out will start charging c 1 as described in stage i. 3.3 stage iii at this stage, lr745 output is turned off and the pwm ic is operating from the v aux supply. the auxiliary volt- age, v aux , can be designed to vary anywhere between the minimum operating v cc voltage of the pwm ic (10v) to the maximum auxiliary voltage rating of the lr745 (22v). figure 3-1: simplified smps using lr745 high voltage v in vout v cc i aux v aux c 1 c 2 d 2 i in gnd lr7 pwm ic
lr745 ds20005394a-page 6 ? 2015 microchip technology inc. figure 3-2: start-up waveforms 12.0 8.0 4.0 0.0 30.0 20.0 10.0 0.0 pwm ic start threshold voltage lr7 v off trip point auxiliary supply powers pwm ic t t t t 16.0 13.5 12.0 8.0 4.0 0.0 v out (v) i in (ma) v aux (v) i aux (ma) v aux = 12v i aux = 20ma i in 0ma 3.0 2.0 1.0 0.0 stage i stage ii stage iii
? 2015 microchip technology inc. ds20005394a-page 7 lr745 3.4 block diagram figure 3-3: block diagram lr745 is a high voltage, switch-mode power supply start-up circuit which has 3 terminals: vin, gnd, and vout. an input voltage range of 35 - 450v dc can be applied directly at the input vin pin. the output voltage, v out , is monitored by the 2 comparators: comp1 and comp2. an internal reference, v ref , and resistor divider r1, r2, and r3set the nominal v out trip points of 7.0v for comp1 and 13.25v for comp2. when a voltage is applied on vin, v out will start to ramp up from 0v. when v out is less than 7.0v, the out- put of comp1 will be at a logic high state, keeping the d flip-flop in a reset state. th e output of the d flip-flop, q, will be at logic low keeping transistor m 2 off. the data input for the d flip-flop, d, is internally connected to a logic high. as v out becomes greater than 7.0v, comp1 will change to a logic low state. v out will continue to increase, and the constant current source, typically 3.0ma output, will charge an external storage capaci- tor. as v out reaches above 13.25v, the output of comp2 will then switch from a logic high to a logic low state. the d flip-flop?s output does not change state since its clock input is designed to trigger only on a ris- ing edge, logic low to logic high transition. when there is no load connected to t he output, the output voltage will continue to increase until it reaches 21.5v, which is the zener voltage minus the threshold voltage of tran- sistor m 1 . the zener voltage is typically 23v, and the threshold voltage of m 1 is typically 1.5v. the zener diode is biased by resistor r 4 . v out will start to decrease when it is connected to an external load greater than the internal constant current source, which is the case when the pwm ic starts up. when v out falls below 13.25v, the output of comp2 will switch from a logic low to a logic high. the output of comp2 will clock in a logic 1 into the d flip-flop, causing the d flip-flop?s output, q, to switch from a logic low to a logic high. transistor m 2 will then be turned on pulling the gate of transistor m 1 to ground, thereby turning transistor m 1 off. transistor m 1 will remain off as long as vout is greater than 7.0v. once v out decreases below 7.0v, comp1 will reset the d flip-flop, thereby turning transistor m 2 off and transistor m 1 back on. clk clock q gnd r d v out vout vin m2 m 1 r 3 2.0 - 4.0m a + 23v - v z v ref reset - comp1 + - comp1 + r 2 r 1 r 4
lr745 ds20005394a-page 8 ? 2015 microchip technology inc. 4.0 design considerations to ensure the best design using lr745, evaluate the value of c 1 and the smps requirements. 4.1 calculating the value for c 1 sizing the v cc capacitor, c 1 , is an important factor. making c 1 too large will cause the smps to power up too slowly. however, if too small, c 1 will not allow the smps to power up due to insufficient charge in the capacitor to power the ic and mosfet until the auxil- iary supply is available. the value of c 1 can be approx- imated by the following equation: definitions: - f = switching frequency - n = number of clock cycles required to charge v aux to v min value - i = pwm operating current -v start = pwm ic start threshold rating -v min = pwm ic minimum v cc operating volt- age consider for example, a pwm ic with a switching fre- quency of 100khz, operating current of 20ma, start threshold of 16v, and a minimum operating voltage of 10v. if 100 clock cycles are required to charge the aux- iliary voltage to 10v, the minimum value of c 1 is calcu- lated as follows: 4.2 smps with wide minimum to maximum load an important point is that the lr745?s output voltage, v out , must discharge to below the nominal v off trip point of 13.25v in order for its output to turn off. if the smps requires a wide minimum to maximum output load variation, it will be difficult to guarantee that v cc will fall below 13.25v under minimum load conditions. consider an smps that is required to power small as well as large loads and is also required to power up quickly. such a smps may power up too fast with a small load, not allowing the v cc voltage to fall below 13.25v. for such conditions, the circuit in figure 4-1 is recommended. in figure 4-1 , the v ref pin of the uc3844 is used to bias the ground pin of the lr745. the v ref pin on the uc3844 is a 5.0v reference, which stays at 0v until the v cc voltage reaches the start threshold voltage. once v cc reaches the start threshold voltage, v ref will switch digitally from 0v to 5.0v. during start-up, the lr745 will be on, and v cc will start to increase up to 16v. once v cc reaches16v, the uc3844 will start to operate and v ref will increase from 0v to 5.0v. the lr745 will see an effective v out voltage of 11v (16v minus 5.0v) because the gr ound of the lr745 is now at 5.0v. the lr745 will immediately turn off its output, vout, without having to wait for the v cc voltage to decrease. the v ref switching from 0 to 5.0v during start is a common feature in most pwm ics. figure 4-1: using v ref for ground voltage c 1 1 f -- - n1 ? ? v start v min ? ------------------------------------ = c 1 1 100khz -------------------- - 100 20ma ? ? 16v 10v ? ---------------------------------------------------------------- - = c 1 3.3 ? f = gnd vin vout vcc vref c 1 pwm ic lr7
? 2015 microchip technology inc. ds20005394a-page 9 lr745 5.0 packaging information 5.1 package marking information legend: xx...x product code or customer-specific information y year code (last digit of calendar year) yy year code (last 2 digits of calendar year) ww week code (week of january 1 is week ?01?) nnn alphanumeric traceability code pb-free jedec ? designator for matte tin (sn) * this package is pb-free. the pb-free jedec designator ( ) can be found on the outer packaging for this package. note : in the event the full microchip part nu mber cannot be marked on one line, it will be carried over to the next line, thus limiting the number of available characters for product code or custom er-specific information. package may or not include the corporate logo. 3 e 3 e 3-lead to-243aa * (sot-89) example xxxyyww nnn lr7513 343 3-lead to-92 ywwnnn xxxxxx xxxx e 3 example 513343 lr745 n3 e 3
lr745 ds20005394a-page 10 ? 2015 microchip technology inc. 3-lead to-243aa (sot-89) package outline (n8) symbol a b b1 c d d1 e e1 e e1 h l dimensions (mm) min 1.40 0.44 0.36 0.35 4.40 1.62 2.29 2.00 ? 1.50 bsc 3.00 bsc 3.94 0.73 ? nom-------- -- max 1.60 0.56 0.48 0.44 4.60 1.83 2.60 2.29 4.25 1.20 jedec registration to-243, variation aa, issue c, july 1986. ? this dimension differs from the jedec drawing drawings not to scale . b b1 d d1 e h e1 c a 12 3 e e1 top view side view l note: for the most current package drawings, see the microchip packaging specification at www.microchip.com/packaging. note: for the most current package drawings, see the microchip packaging specification at www.microchip.com/packaging.
? 2015 microchip technology inc. ds20005394a-page 11 lr745 note: for the most current package drawings, see the microchip packaging specification at www.microchip.com/packaging.
lr745 ds20005394a-page 12 ? 2015 microchip technology inc. appendix a: revision history revision a (april 2015) ? update file to new format
? 2015 microchip technology inc. ds20005394a-page 13 lr745 product identification system to order or obtain information, e.g., on pricing or de livery, refer to the factory or the listed sales office . device: lr745 = high-input, voltage smps, start-up/linear regulator package: n3 = to-92 (fixed voltage) n8 = to-243aa (sot-89) (fixed voltage) environmental g = lead (pb)-free/rohs-compliant package media type: (blank) = 1000/bag for n3 packages = 2000/reel for n8 packages p003 = 2000/reel for n3 package p013 = 2000/ammo pack for n3 package examples: a) lr745n3-g to-92 package, 1000/bag b) LR745N3-G-P003: to-92 package, 2000/reel. c) lr745n3-g-p013: to-92 package, 2000/ammo pack. d) lr745n8-g to-243aa package, 2000/reel part no. x device x environmental x x package options media - - type
ds20005394a-page 14 ? 2015 microchip technology inc. information contained in this publication regarding device applications and the like is prov ided only for your convenience and may be superseded by updates. it is your responsibility to ensure that your application me ets with your specifications. microchip makes no representations or warranties of any kind whether express or implied, written or oral, statutory or otherwise, related to the information, including but not limited to its condition, quality, performance, merchantability or fitness for purpose . microchip disclaims all liability arising from this information and its use. use of microchip devices in life support and/or safe ty applications is entirely at the buyer?s risk, and the buyer agrees to defend, indemnify and hold harmless microchip from any and all damages, claims, suits, or expenses resulting fr om such use. no licenses are conveyed, implicitly or ot herwise, under any microchip intellectual property rights. trademarks the microchip name and logo, th e microchip logo, dspic, flashflex, flexpwr, jukeblox, k ee l oq , k ee l oq logo, kleer, lancheck, medialb, most, most logo, mplab, optolyzer, pic, picstart, pic 32 logo, righttouch, spynic, sst, sst logo, superflash and uni/o are registered trademarks of microchip te chnology incorporated in the u.s.a. and other countries. the embedded control solutions company and mtouch are registered trademarks of microc hip technology incorporated in the u.s.a. analog-for-the-digital age, bodycom, chipkit, chipkit logo, codeguard, dspicdem, dspicdem.net, ecan, in-circuit serial programming, icsp, inter-chip connectivity, kleernet, kleernet logo, miwi, mpasm, mpf, mplab certified logo, mplib, mplink, multitrak, netdetach, omniscient code generation, picdem, picdem.net, pickit, pictail, righttouch logo, real ice, sqi, serial quad i/o, total endurance, tsharc, usbcheck, varisense, viewspan, wiperlock, wireless dna, and zena are trademarks of microchip technology incorporated in the u.s.a. and other countries. sqtp is a service mark of mi crochip technology incorporated in the u.s.a. silicon storage technology is a registered trademark of microchip technology inc. in other countries. gestic is a registered tradem arks of microchip technology germany ii gmbh & co. kg, a subsidiary of microchip technology inc., in other countries. all other trademarks mentioned herein are property of their respective companies. ? 2015, microchip technology incorporated, printed in the u.s.a., all rights reserved. isbn: 978-1-63277-243-5 note the following details of the code protection feature on microchip devices: ? microchip products meet the specification cont ained in their particular microchip data sheet. ? microchip believes that its family of products is one of the mo st secure families of its kind on the market today, when used i n the intended manner and under normal conditions. ? there are dishonest and possibly illegal meth ods used to breach the code protection fe ature. all of these methods, to our knowledge, require using the microchip pr oducts in a manner outside the operating specif ications contained in microchip?s data sheets. most likely, the person doing so is engaged in theft of intellectual property. ? microchip is willing to work with the customer who is concerned about the integrity of their code. ? neither microchip nor any other semiconduc tor manufacturer can guarantee the security of their code. code protection does not mean that we are guaranteeing the product as ?unbreakable.? code protection is constantly evolving. we at microchip are committed to continuously improving the code protection features of our products. attempts to break microchip?s c ode protection feature may be a violation of the digital millennium copyright act. if such acts allow unauthorized access to your softwa re or other copyrighted work, you may have a right to sue for relief under that act. microchip received iso/ts-16949:2009 certification for its worldwide headquarters, design and wafer fabrication facilities in chandler and tempe, arizona; gresham, oregon and design centers in california and india. the company?s quality system processes and procedures are for its pic ? mcus and dspic ? dscs, k ee l oq ? code hopping devices, serial eeproms, microperi pherals, nonvolatile memory and analog products. in addition, microchip?s quality system for the design and manufacture of development systems is iso 9001:2000 certified. quality management s ystem by dnv == iso/ts 16949 ==
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