simple step-up voltage regulator requires few external components npn output switches 3.0a, 65v(max) extended input voltage range: 3.0v to 40v current mode operation for improved transient response, line regulation, and current limiting soft start function provides controlled startup 52khz internal oscillator output switch protected by current limit, undervoltage lockout and thermal shutdown improved replacement for lm2577-adj series the uc2577-adj device provides all the active functions neces- sary to implement step-up (boost), flyback, and forward converter switching regulators. requiring only a few components, these sim- ple regulators efficiently provide up to 60v as a step-up regulator, and even higher voltages as a flyback or forward converter regula- tor. the uc2577-adj features a wide input voltage range of 3.0v to 40v and an adjustable output voltage. an on-chip 3.0a npn switch is included with undervoltage lockout, thermal protection circuitry, and current limiting, as well as soft start mode operation to reduce current during startup. other features include a 52khz fixed fre- quency on-chip oscillator with no external components and current mode control for better line and load regulation. a standard series of inductors and capacitors are available from several manufacturers optimized for use with these regulators and are listed in this data sheet. uc2577-adj 3/97 features description connection diagram block diagram udg-94034 simple boost and flyback converters sepic topology permits input voltage to be higher or lower than output voltage transformer coupled forward regulators multiple output designs typical applications 5-pin to-220 (top view) t package also available in to-263 package (td).
parameter test conditions min typ max units system parameters circuit figure 1 (note 3) output voltage vin = 5v to 10v, i load = 100ma to 800ma 11.40 12.0 12.60 v t j = 25 c 11.60 12.40 v line regulation vin = 3.0v to 10v, i load = 300ma 20 100 mv t j = 25 c50mv load regulation vin = 5v, i load = 100ma to 800ma 20 100 mv t j = 25 c50mv efficiency vin = 5v, i load = 800ma 80 % device parameters input supply current v fb = 1.5v (switch off) 7.5 14 ma t j = 25 c10ma i switch = 2.0a, v comp = 2.0v (max duty cycle) 45 85 ma t j = 25 c70ma input supply uvlo i switch = 100ma 2.70 2.95 v t j = 25 c2.85v oscillator frequency measured at switch pin, i switch = 100ma 42 52 62 khz t j = 25 c4856khz reference voltage measured at fb pin, vin = 3.0v to 40v, v comp = 1.0v 1.206 1.230 1.254 v t j = 25 c 1.214 1.246 v reference voltage line regulation vin = 3.0v to 40v 0.5 mv error amp input bias current v comp = 1.0v 100 800 na t j = 25 c 300 na error amp transconductance i comp = - 30 m a to +30 m a, v comp = 1.0v 1600 3700 5800 m mho t j = 25 c 2400 4800 m mho error amp voltage gain v comp = 0.8v to 1.6v, r comp = 1.0mw (note 4) 250 800 v/v t j = 25 c 500 v/v error amplifier output swing upper limit v fb = 1.0v 2.0 2.4 v t j = 25 c2.2v lower limit v fb = 1.5v 0.3 0.55 v t j = 25 c0.40v error amp output current v fb = 1.0v to 1.5v, v comp = 1.0v 90 200 400 m a t j = 25 c 130 300 m a soft start current v fb = 1.0v, v comp = 0.5v 1.5 5.0 9.5 m a t j = 25 c2.57.5 m a maximum duty cycle v comp = 1.5v, i switch = 100ma 90 95 % t j = 25 c93% unless otherwise stated, these specifications apply for t a = - 40 c to +125 c, vin = 5v, v fb = v ref , i switch = 0, and t a =t j . electrical characteristics recommended operating range supply voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45v output switch voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65v output switch current (note 2) . . . . . . . . . . . . . . . . . . . . . 6.0a power dissipation . . . . . . . . . . . . . . . . . . . . . . internally limited storage temperature range . . . . . . . . . . . . . - 65 c to +150 c lead temperature (soldering, 10 sec.) . . . . . . . . . . . . . . 260 c maximum junction temperature . . . . . . . . . . . . . . . . . . . 150 c minimum esd rating (c = 100pf, r = 15k w ) . . . . . . . . . . . 2kv absolute maximum ratings (note 1) uc2577-adj supply voltage . . . . . . . . . . . . . . . . . . . . . . . . 3.0v vin 40v output switch voltage . . . . . . . . . . . . . . . 0v v switch 60v output switch current . . . . . . . . . . . . . . . . . . . . i switch 3.0a junction temperature range . . . . . . . . . . - 40 c t j +125 c 2
uc2577-adj parameter test conditions min typ max units device parameters (cont.) switch transconductance 12.5 a/v switch leakage current v switch = 65v, v fb = 1.5v (switch off) 10 600 m a t j = 25 c300 m a switch saturation voltage i switch = 2.0a, v comp = 2.0v (max duty cycle) 0.5 0.9 v t j = 25 c0.7v npn switch current limit v comp = 2.0v 3.0 4.3 6.0 a thermal resistance junction to ambient 65 c/w junction to case 2 c/w comp pin current v comp = 0 25 50 m a t j = 25 c40 m a unless otherwise stated, these specifications apply for t a = - 40 c to +125 c, vin = 5v, v fb = v ref , i switch = 0, and t a =t j . electrical characteristics note 1: absolute maximum ratings indicate limits beyond which damage to the device may occur. operating ratings indicate conditions during which the device is intended to be functional, but device parameter specifications may not be guaranteed under these conditions. for guaranteed specifications and test conditions, see the electrical characteristics. note 2: output current cannot be internally limited when the uc2577 is used as a step-up regulator. to prevent damage to the switch, its current must be externally limited to 6.0a. however, output current is internally limited when the uc2577 is used as a flyback or forward converter regulator. note 3. external components such as the diode, inductor, input and output capacitors can affect switching regulator performance. when the uc2577 is used as shown in the test circuit, system performance will be as specified by the system parameters. note 4: a 1.0m w resistor is connected to the compensation pin (which is the error amplifiers output) to ensure accuracy in measuring a vol. in actual applications, this pins load resistance should be 3 10m w , resulting in a vol that is typically twice the guaranteed minimum limit. figure 1. circuit used to specify system parameters udg-94035 l = 415-0930 (aie) d = any manufacturer c out = sprague type 673d electrolytic 680 m f, 2 0 v r1 = 48.7k in series with 511 w (1%) r2 = 5.62k (1%) 3
the block diagram shows a step-up switching regulator utilizing the uc2577. the regulator produces an output voltage higher than the input voltage. the uc2577 turns its switch on and off at a fixed frequency of 52khz, thus storing energy in the inductor (l). when the npn switch is on, the inductor current is charged at a rate of vin/l. when the switch is off, the voltage at the switch termi- nal of the inductor rises above vin, discharging the stored current through the output diode (d) into the out- put capacitor (c out ) at a rate of (v out - vin)/l. the en- ergy stored in the inductor is thus transferred to the output. the output voltage is controlled by the amount of energy transferred, which is controlled by modulating the peak inductor current. this modulation is accomplished by feeding a portion of the output voltage to an error ampli- fier which amplifies the difference between the feedback voltage and an internal 1.23v precision reference volt- age. the output of the error amplifier is then compared to a voltage proportional to the switch current, or the induc- tor current, during the switch on time. a comparator ter- minates the switch on time when the two voltages are equal and thus controls the peak switch current to main- tain a constant output voltage. figure 2 shows voltage and current waveforms for the circuit. formulas for calcu- lation are shown in figure 3. step-up regulator design procedure refer to the block diagram given: v inmin = minimum input supply voltage v out = regulated output voltage uc2577-adj step-up (boost) regulator duty cycle d v out + v f - v in v out + v f - v sat ? v out - v in v out avg. inductor current i ind(avg) i load 1 - d inductor current ripple d i ind v in - v sat l d 52,000 peak inductor current i ind(pk) i load 1 - d + d i ind 2 peak switch current i sw(pk) i load 1 - d + d i ind 2 switch voltage when off v sw(off) v out + v f diode reverse voltage v r v out - v sat avg. diode current i d(avg) i load peak diode current i d(pk) i load 1 - d + d i ind 2 . power dissipation p d 0.25 w ? ? i load 1 - d ? ? 2 d + i load d v in 50 ( 1 - d ) v f = forward biased diode voltage, i load = output load figure 2. step-up regulator waveforms first, determine if the uc2577 can provide these values of v out and i loadmax when operating with the minimum value of v in . the upper limits for v out and i loadmax are given by the following equations. v out 60v and v out 10 v inmin i loadmax 2.1a v inmin v out these limits must be greater than or equal to the values specified in this application. 1. output voltage section resistors r1 and r2 are used to select the desired out- put voltage. these resistors form a voltage divider and present a portion of the output voltage to the error ampli- fier which compares it to an internal 1.23v reference. se- lect r1 and r2 such that: r1 r2 = v out 1.23v - 1 figure 3. step-up regulator formulas applications information 4
2. inductor selection (l) a. preliminary calculations to select the inductor, the calculation of the following three parameters is necessary: dmax, the maximum switch duty cycle (0 d 0.9): d max = v out + v f - v inmin v out + v f - 0.6v where typically v f = 0.5v for schottky diodes and v f = 0.8v for fast recovery diodes. e t, the product of volts time that charges the induc- tor: e t = d max ( v inmin - 0.6v ) 10 6 52,000hz ( v m s ) i ind, dc , the average inductor current under full load: i ind, dc = 1.05 i loadmax 1 - d max b. identify inductor value: 1. from figure 4, identify the inductor code for the region indicated by the intersection of e t and i ind, dc . this code gives the inductor value in microhenries. the l or h prefix signifies whether the inductor is rated for a maxi- mum e t of 90v m s (l) or 250v m s (h). 2. if d < 0.85, go to step c. if d 3 0.85, calculate the minimum inductance needed to ensure the switching regulators stability: 0.3 0.4 0.45 0.35 0.5 0.6 0.7 0.8 0.9 1.0 1.5 2.0 2.5 3.0 20 30 35 25 40 45 50 60 70 80 90 100 200 150 l47 l68 l100 l150 l220 l330 h2200 l680 h1500 h1000 h680 h470 h330 h220 h150 l470 et (v m s) i ind, dc (a) figure 4. inductor selection graph if l min is smaller than the inductor values found in step b1, go on to step c. otherwise, the inductor value found in step b1 is too low; an appropriate inductor code should be obtained from the graph as follows: 1. find the lowest value inductor that is greater than l min . 2. find where e t intersects this inductor value to determine if it has an l or h prefix. if e t intersects both the l and h regions, select the inductor with an h prefix. c. inductor selection select an inductor from the table of figure 5 which cross references the inductor codes to the part numbers of the three different manufacturers. the inductors listed in this table have the following characteristics: aie (ferrite, pot-core inductors): benefits of this type are low etectromagnetic interference (emi), small physical size, and very low power dissipation (core loss). pulse (powdered iron, toroid core inductors): bene- fits are low emi and ability to withstand e t and peak current above rated value better than ferrite cores. renco (ferrite, bobbin-core inductors): benefits are low cost and best ability to withstand e t and peak current above rated value. be aware that these in- ductors generate more emi than the other types, and this may interfere with signals sensitive to noise. uc2577-adj note: this chart assumes that the inductor ripple current inductor is approximately 20% to 30% of the average inductor current (when the regulator is under full load). greater ripple current causes higher peak switch currents and greater output ripple vo lt- age. lower ripple current is achieved with larger value inductors. the factor of 20% to 30% is chosen as a convenient balance between the two extremes. applications information (cont.) 5
uc2577-adj 3. compensation network (r c , c c ) and output capacitor (c out ) selection the compensation network consists of resistor r c and capacitor c c which form a simple pole-zero network and stabilize the regulator. the values of r c and c c depend upon the voltage gain of the regulator, i loadmax , the in- ductor l, and output capacitance c out . a procedure to calculate and select the values for r c , c c, and c out which ensures stability is described below. it should be noted, however, that this may not result in optimum com- pensation. to guarantee optimum compensation a stand- ard procedure for testing loop stability is recommended, such as measuring v out transient responses to pulsing i load . a. calculate the maximum value for r c . r c 750 i loadmax v out 2 v inmin 2 select a resistor less than or equal to this value, not to exceed 3k w . b. calculate the minimum value for c out using the fol- lowing two equations. c out 3 0.19 l r c i loadmax v inmin v out and c out 3 v inmin r c ( v inmin + ( 3.74 10 5 l )) 487,800 v out 3 the larger of these two values is the minimum value that ensures stability. c. calculate the minimum value of c c . c c 3 58.5 v out 2 c out r c 2 v inmin the compensation capacitor is also used in the soft start function of the regulator. when the input voltage is ap- plied to the part, the switch duty cycle is increased slowly at a rate defined by the compensation capacitor and the soft start current, thus eliminating high input currents. without the soft start circuitry, the switch duty cycle would instantly rise to about 90% and draw large currents from the input supply. for proper soft starting, the value for c c should be equal or greater than 0.22 m f. figure 6 lists several types of aluminum electrolytic ca- pacitors which could be used for the output filter. use the following parameters to select the capacitor. working voltage (wvdc): choose a capacitor with a working voltage at least 20% higher than the regulator output voltage. ripple current: this is the maximum rms value of cur- rent that charges the capacitor during each switching cy- cle. for step-up and flyback regulators, the formula for ripple current is: i ripplerms = i loadmax d max 1 - d max choose a capacitor that is rated at least 50% higher than this value at 52khz. equivalent series resistance (esr): this is the primary cause of output ripple voltage, and it also affects the val- ues of r c and c c needed to stabilize the regulator. as a result, the preceding calculations for c c and r c are only valid if the esr does not exceed the maximum value specified by the following equations. esr 0.01 15v i ripple ( p - p ) and 8.7 10 - 3 v in i loadmax where i ripple ( p - p ) = 1.15 i loadmax 1 - d max select a capacitor with an esr, at 52khz, that is less than or equal to the lower value calculated. most electro- lytic capacitors specify esr at 120khz which is 15% to 30% higher than at 52khz. also, note that esr increases by a factor of 2 when operating at - 20 c. in general, low values of esr are achieved by using large value capacitors (c 3 470 m f), and capacitors with high wvdc, or by paralleling smaller value capacitors. inductor code manufacturers part number aie pulse renco l47 415 - 0932 pe - 53112 rl2442 l68 415 - 0931 pe - 92114 rl2443 l100 415 - 0930 pe - 92108 rl2444 l150 415 - 0953 pe - 53113 rl1954 l220 415 - 0922 pe - 52626 rl1953 l330 415 - 0926 pe - 52627 rl1952 l470 415 - 0927 pe - 53114 rl1951 l680 415 - 0928 pe - 52629 rl1950 h150 415 - 0936 pe - 53115 rl2445 h220 430 - 0636 pe - 53116 rl2446 h330 430 - 0635 pe - 53117 rl2447 h470 430 - 0634 pe - 53118 rl1961 h680 415 - 0935 pe - 53119 rl1960 h1000 415 - 0934 pe - 53120 rl1959 h1500 415 - 0933 pe - 53121 rl1958 h2200 415 - 0945 pe - 53122 rl2448 aie magnetics, div. vernitron corp., (813)347-2181 2801 72nd street north, st. petersburg, fl 33710 pulse engineering, (619)674-8100 12220 world trade drive, san diego, ca 92128 renco electronics, inc., (516)586-5566 60 jeffryn blvd. east, deer park, ny 11729 figure 5. table of standardized inductors and manufacturers part numbers applications information (cont.) 6
unitrode corporation 7 continental blvd. merrimack, nh 03054 tel. (603) 424-2410 fax (603) 424-3460 4. input capacitor selection (c in ) to reduce noise on the supply voltage caused by the switching action of a step-up regulator (ripple current noise), vin should be bypassed to ground. a good qual- ity 0.1 m f capacitor with low esr should provide suffi- cient decoupling. if the uc2577 is located far from the supply source filter capacitors, an additional electrolytic (47 m f, for example) is required. nichicon - types pf, px, or pz 927 east stateparkway, schaumburg, il 60173 (708)843-7500 united chemi-con - types lx, sxf, or sxj 9801 west higgens, rosemont, il 60018 (708)696-2000 figure 6. aluminum electrolytic capacitors recommended for switching regulators 5. output diode selection (d) in the step-up regulator, the switching diode must with- stand a reverse voltage and be able to conduct the peak output current of the uc2577. therefore a suitable diode must have a minimum reverse breakdown voltage greater than the circuit output voltage, and should also be rated for average and peak current greater than i loadmax and i dpk . because of their low forward voltage drop (and thus higher regulator efficiencies), schottky barrier diodes are often used in switching regulators. re- fer to figure 7 for recommended part numbers and volt- age ratings of 1a and 3a diodes. v outmax schottky fast recovery 1a 3a 1a 3a 20v 1n5817 1n5820 mbr120p mbr320p 30v 1n5818 1n5821 mbr130p mbr330p 11dq03 31dq03 40v 1n5819 1n5822 mbr140p mbr340p 11dq04 31dq04 50v mbr150 mbr350 1n4933 11dq05 31dq05 mur105 100v 1n4934 mr851 mur110 30dl1 10dl1 mr831 mbrxxx and murxxx are manufactured by motorola. 1ddxxx, 11cxx and 31dxx are manufactured by international rectifier figure 7. diode selection chart uc2577-adj ordering information unitrode type number uc2577t-adj 5 pin to-220 plastic package UC2577TD-ADJ 5 pin to-263 plastic package applications information (cont.) 7
important notice texas instruments and its subsidiaries (ti) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. all products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. ti warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with ti's standard warranty. testing and other quality control techniques are utilized to the extent ti deems necessary to support this warranty. specific testing of all parameters of each device is not necessarily performed, except those mandated by government requirements. certain applications using semiconductor products may involve potential risks of death, personal injury, or severe property or environmental damage (acritical applicationso). ti semiconductor products are not designed, authorized, or warranted to be suitable for use in life-support devices or systems or other critical applications. inclusion of ti products in such applications is understood to be fully at the customer's risk. in order to minimize risks associated with the customer's applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. ti assumes no liability for applications assistance or customer product design. ti does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right of ti covering or relating to any combination, machine, or process in which such semiconductor products or services might be or are used. ti's publication of information regarding any third party's products or services does not constitute ti's approval, warranty or endorsement thereof. copyright ? 1999, texas instruments incorporated
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