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device operating temperature range package semiconductor technical data easy switcher ? 0.5 a stepdown voltage regulator ordering information lm2574dwadj t a = 40 to +125 c so16l n suffix plastic package case 626 (dip8) 8 1 pin connections order this document by lm2574/d device type/nominal output voltage lm25743.3 lm25745 lm257412 lm257415 lm2574adj 3.3 v 5.0 v 12 v 15 v 1.23 v to 37 v xx = voltage option, i.e, 3.3, 5, 12, 15 v; and adj for adjustable output. * no internal connection, but should be soldered to * pc board for best heat transfer. * (top view) 12 pwr gnd on /off * * * * 11 10 9 5 6 7 8 lm2574nxx dip8 dw suffix plastic package case 751g (so16l) 16 1 * 16 * * fb sig gnd output * v in 15 14 13 1 2 3 4 * * (top view) 8 fb sig gnd on /off pwr gnd output * v in 7 6 5 1 2 3 4 ?
the lm2574 series of regulators are monolithic integrated circuits ideally suited for easy and convenient design of a stepdown switching regulator (buck converter). all circuits of this series are capable of driving a 0.5 a load with excellent line and load regulation. these devices are available in fixed output voltages of 3.3 v, 5.0 v, 12 v, 15 v, and an adjustable output version. these regulators were designed to minimize the number of external components to simplify the power supply design. standard series of inductors optimized for use with the lm2574 are offered by several different inductor manufacturers. since the lm2574 converter is a switchmode power supply, its efficiency is significantly higher in comparison with popular threeterminal linear regulators, especially with higher input voltages. in most cases, the power dissipated by the lm2574 regulator is so low, that the copper traces on the printed circuit board are normally the only heatsink needed and no additional heatsinking is required. the lm2574 features include a guaranteed 4% tolerance on output voltage within specified input voltages and output load conditions, and 10% on the oscillator frequency ( 2% over 0 c to +125 c). external shutdown is included, featuring 60 m a (typical) standby current. the output switch includes cyclebycycle current limiting, as well as thermal shutdown for full protection under fault conditions. features ? 3.3 v, 5.0 v, 12 v, 15 v, and adjustable output versions ? adjustable version output voltage range, 1.23 to 37 v 4% max over line and load conditions ? guaranteed 0.5 a output current ? wide input voltage range: 4.75 to 40 v ? requires only 4 external components ? 52 khz fixed frequency internal oscillator ? ttl shutdown capability, low power standby mode ? high efficiency ? uses readily available standard inductors ? thermal shutdown and current limit protection applications ? simple and highefficiency stepdown (buck) regulators ? efficient preregulator for linear regulators ? oncard switching regulators ? positive to negative converters (buckboost) ? negative stepup converters ? power supply for battery chargers ? motorola, inc. 1999 rev 2, 07/1999
lm2574 2 motorola analog ic device data figure 1. block diagram and typical application 7.0 40 v unregulated dc input l1 330 m h pwr gnd +v in 5 c in 22 m f 4on /off 3 output 7 feedback 1 d1 1n5819 c out 220 m f typical application (fixed output voltage versions) representative block diagram and typical application unregulated dc input +v in 5 c out feedback 1 c in l1 d1 r2 r1 1.0 k output 7 pwr gnd 4 on /off 3 reset latch thermal shutdown 52 khz oscillator 1.235 v bandgap reference freq shift 18 khz comparator fixed gain error amplifier current limit driver 1.0 amp switch on /off 3.1 v internal regulator v out load output voltage versions 3.3 v 5.0 v 12 v 15 v r2 ( w ) 1.7 k 3.1 k 8.84 k 11.3 k for adjustable version r1 = open, r2 = 0 w lm2574 5.0 v regulated output 0.5 a load sig gnd 2 sig gnd 2 absolute maximum ratings (absolute maximum ratings indicate limits beyond which damage to the device may occur). rating symbol value unit maximum supply voltage v in 45 v on /off pin input voltage 0.3 v v +v in v output voltage to ground (steady state) 1.0 v dw suffix, plastic package case 751g max power dissipation p d internally limited w thermal resistance, junctiontoair r q ja 145 c/w n suffix, plastic package case 626 max power dissipation p d internally limited w thermal resistance, junctiontoambient r q ja 100 c/w thermal resistance, junctiontocase r q jc 5.0 c/w storage temperature range t stg 65 c to +150 c c minimum esd rating 2.0 kv (human body model: c = 100 pf, r = 1.5 k w ) lead temperature (soldering, 10 seconds) 260 c maximum junction temperature t j 150 c note: esd data available upon request.
lm2574 3 motorola analog ic device data operating ratings (operating ratings indicate conditions for which the device is intended to be functional, but do not guarantee specific performance limits. for guaranteed specifications and test conditions, see the electrical characteristics). rating symbol value unit operating junction temperature range t j 40 to +125 c supply voltage v in 40 v system parameters ([note 1] test circuit figure 16) electrical characteristics (unless otherwise specified, v in = 12 v for the 3.3 v, 5.0 v, and adjustable version, v in = 25 v for the 12 v version, v in = 30 v for the 15 v version. i load = 100 ma. for typical values t j = 25 c, for min/max values t j is the operating junction temperature range that applies [note 2], unless otherwise noted). characteristic symbol min typ max unit lm25743.3 ([note 1] test circuit figure 16) output voltage (v in = 12 v, i load = 100 ma, t j = 25 c) v out 3.234 3.3 3.366 v output voltage (4.75 v v in 40 v, 0.1 a i load 0.5 a) v out v t j = 25 c 3.168 3.3 3.432 t j = 40 to +125 c 3.135 3.465 efficiency (v in = 12 v, i load = 0.5 a) h 72 % lm25745 ([note 1] test circuit figure 16) output voltage (v in = 12 v, i load = 100 ma, t j = 25 c) v out 4.9 5.0 5.1 v output voltage (7.0 v v in 40 v, 0.1 a i load 0.5 a) v out v t j = 25 c 4.8 5.0 5.2 t j = 40 to +125 c 4.75 5.25 efficiency (v in = 12 v, i load = 0.5 a) h 77 % lm257412 ([note 1] test circuit figure 16) output voltage (v in = 25 v, i load = 100 ma, t j = 25 c) v out 11.76 10 12.24 v output voltage (15 v v in 40 v, 0.1 a i load 0.5 a) v out v t j = 25 c 11.52 12 12.48 t j = 40 to +125 c 11.4 12.6 efficiency (v in = 15 v, i load = 0.5 a) h 88 % lm257415 ([note 1] test circuit figure 16) output voltage (v in = 30 v, i load = 100 ma, t j = 25 c) v out 14.7 15 15.3 v output voltage (18 v < v in < 40 v, 0.1 a < i load < 0.5 a) v out v t j = 25 c 14.4 15 15.6 t j = 40 to +125 c 14.25 15.75 efficiency (v in = 18 v, i load = 0.5 a) h 88 % lm2574 adjustable version ([note 1] test circuit figure 16) feedback voltage v in = 12 v, i load = 100 ma, v out = 5.0 v, t j = 25 c v fb 1.217 1.23 1.243 v feedback voltage 7.0 v v in 40 v, 0.1 a i load 0.5 a, v out = 5.0 v v fbt v t j = 25 c 1.193 1.23 1.267 t j = 40 to +125 c 1.18 1.28 efficiency (v in = 12 v, i load = 0.5 a, v out = 5.0 v) h 77 % notes: 1. external components such as the catch diode, inductor, input and output capacitors can affect the switching regulator system performance. when the lm2574 is used as shown in the figure 16 test circuit, the system performance will be as shown in the system parameters section of the electrical characteristics. 2. tested junction temperature range for the lm2574: t low = 40 c t high = +125 c
lm2574 4 motorola analog ic device data system parameters ([note 1] test circuit figure 16) electrical characteristics (continued) (unless otherwise specified, v in = 12 v for the 3.3 v, 5.0 v, and adjustable version, v in = 25 v for the 12 v version, v in = 30 v for the 15 v version. i load = 100 ma. for typical values t j = 25 c, for min/max values t j is the operating junction temperature range that applies [note 2], unless otherwise noted). characteristic unit max typ min symbol all output voltage versions feedback bias current v out = 5.0 v (adjustable version only) i b na t j = 25 c 25 100 t j = 40 to +125 c 200 oscillator frequency (note 3) f o khz t j = 25 c 52 t j = 0 to +125 c 47 52 58 t j = 40 to +125 c 42 63 saturation voltage (i out = 0.5 a, [note 4]) v sat v t j = 25 c 1.0 1.2 t j = 40 to +125 c 1.4 max duty cycle (aono) [note 5] dc 93 98 % current limit peak current (notes 3 and 4) i cl a t j = 25 c 0.7 1.0 1.6 t j = 40 to +125 c 0.65 1.8 output leakage current (notes 6 and 7), t j = 25 c i l ma output = 0 v 0.6 2.0 output = 1.0 v 10 30 quiescent current (note 6) i q ma t j = 25 c 5.0 9.0 t j = 40 to +125 c 11 standby quiescent current (on /off pin = 5.0 v (aoffo)) i stby m a t j = 25 c 60 200 t j = 40 to +125 c 400 on /off pin logic input level v v out = 0 v v ih t j = 25 c 2.2 1.4 t j = 40 to +125 c 2.4 nominal output voltage v il t j = 25 c 1.2 1.0 t j = 40 to +125 c 0.8 on /off p in input current m a on /off p in = 5.0 v (aoffo), t j = 25 c i ih 15 30 on /off p in = 0 v (aono), t j = 25 c i il 0 5.0 notes: 1. external components such as the catch diode, inductor, input and output capacitors can affect the switching regulator system performance. when the lm2574 is used as shown in the figure 16 test circuit, the system performance will be as shown in the system parameters section of the electrical characteristics. 2. tested junction temperature range for the lm2574: t low = 40 c t high = +125 c 3. the oscillator frequency reduces to approximately 18 khz in the event of an output short or an overload which causes the regulated output voltage to drop approximately 40% from the nominal output voltage. this self protection feature lowers the average power dissipation of the ic by lowering the minimum duty cycle from 5% down to approximately 2%. 4. output (pin 2) sourcing current. no diode, inductor or capacitor connected to the output pin. 5. feedback (pin 4) removed from output and connected to 0 v. 6. feedback (pin 4) removed from output and connected to 12 v for the adjustable, 3.3 v, and 5.0 v versions, and 25 v for the 12 v and 15 v versions, to force the output transistor off. 7. v in = 40 v.
lm2574 5 motorola analog ic device data i stby , standby quiescent current ( a) m i q , quiescent current (ma) v out , output voltage change (%) t j , junction temperature ( c) i o , output current (a) t j , junction temperature ( c) v in , input voltage (v) v in , input voltage (v) input output differential (v) t j , junction temperature ( c) v out , output voltage change (%) figure 2. normalized output voltage t j , junction temperature ( c) figure 3. line regulation v in = 20 v i load = 100 ma normalized at t j = 25 c figure 4. dropout voltage figure 5. current limit figure 6. quiescent current figure 7. standby quiescent current i load = 100 ma t j = 25 c 3.3 v, 5.0 v and adj 12 v and 15 v v in = 25 v i load = 100 ma i load = 500 a v in = 12 v v in = 40 v l = 300 m h i load = 500 ma i load = 100 ma v out = 5.0 v measured at ground pin t j = 25 c v on /off = 5.0 v typical performance characteristics (circuit of figure 16) 1.0 0.8 0.6 0.4 0.2 0 0.2 0.4 0.6 0.8 1.0 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0.2 0.4 0.6 2.0 1.5 1.0 0.5 0 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 20 18 16 14 12 10 8.0 6.0 4.0 200 180 160 140 120 100 80 60 40 20 0 125 100 75 60 25 0 25 50 40 35 30 25 20 15 10 5.0 0 125 100 75 60 25 0 25 50 125 100 75 60 25 0 25 50 40 35 30 25 20 15 10 5.0 0 125 100 75 60 25 0 25 50
lm2574 6 motorola analog ic device data , input voltage (v) v in v sat , saturation voltage (v) i fb , feedback pin current (na) a b c 5 m s/div t j , junction temperature ( c) switch current (a) 5 m s/div t j , junction temperature ( c) normalized frequency (%) figure 8. oscillator frequency t j , junction temperature ( c) figure 9. switch saturation voltage figure 10. minimum operating voltage figure 11. feedback pin current figure 12. continuous mode switching waveforms v out = 5.0 v, 500 ma load current, l = 330 m h figure 13. discontinuous mode switching waveforms v out = 5.0 v, 100 ma load current, l = 100 m h v in = 1.23 v i load = 100 ma adjustable version only v in = 12 v normalized at 25 c adjustable version only a b c a: output pin voltage, 10 v/div. b: inductor current, 0.2 a/div. c: output ripple voltage, 20 mv/div, accoupled a: output pin voltage, 10 v/div. b: inductor current, 0.2 a/div. c: output ripple voltage, 20 mv/div, accoupled typical performance characteristics (circuit of figure 16) (continued) 8.0 6.0 4.0 2.0 0 2.0 4.0 6.0 8.0 10 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 100 80 60 40 20 0 20 40 60 80 100 125 100 75 50 25 0 25 50 0 0.1 0.2 0.3 0.4 0.5 125 100 75 50 25 0 25 50 125 100 75 50 25 0 25 50 20 v 10 v 0 0.6 a 0.4 a 0.2 a 0 20 mv ac 20 v 10 v 0 0.6 a 0.4 a 0.2 a 0 20 mv ac 40 c 25 c 125 c
lm2574 7 motorola analog ic device data a b 200 m s/div 200 m s/div figure 14. 500 ma load transient response for continuous mode operation, l = 330 m h, c out = 300 m f figure 15. 250 ma load transient response for discontinuous mode operation, l = 68 m h, c out = 470 m f a: output voltage, 50 mv/div, ac coupled b: 100 ma to 500 ma load pulse a b a: output voltage, 50 mv/div, ac coupled b: 50 ma to 250 ma load pulse typical performance characteristics (circuit of figure 16) (continued) 50 mv ac 500 ma 0 50 mv ac 200 ma 100 ma 0
lm2574 8 motorola analog ic device data figure 16. test circuit and layout guidelines d1 1n5819 l1 330 m h output 7 1 feedback c out 220 m f c in 22 m f lm2574 fixed output 1 3 4on /off pwr gnd v in load v out d1 1n5819 l1 330 m h output 7 1 feedback c out 220 m f c in 22 m f lm2574 adjustable 1 v in load v out 5.0 v fixed output voltage versions adjustable output voltage versions v out v ref 1.0 r2 r1 r2 r1 v out v ref 1.0 where v ref = 1.23 v, r1 between 1.0 k w and 5.0 k w r2 6.12 k r1 2.0 k 7.0 40 v unregulated dc input 2 sig gnd 3 4on /off pwr gnd 2 sig gnd 7.0 v 40 v unregulated dc input c in 22 m f, 60 v, aluminium electrolytic c out 220 m f, 25 v, aluminium electrolytic d1 schottky, 1n5819 l1 330 m h, (for 5.0 v in , 3.3 v out , use 100 m h) r1 2.0 k, 0.1% r2 6.12 k, 0.1% pcb layout guidelines as in any switching regulator, the layout of the printed circuit board is very important. rapidly switching currents associated with wiring inductance, stray capacitance and parasitic inductance of the printed circuit board traces can generate voltage transients which can generate electromagnetic interferences (emi) and affect the desired operation. as indicated in the figure 16, to minimize inductance and ground loops, the length of the leads indicated by heavy lines should be kept as short as possible. for best results, singlepoint grounding (as indicated) or ground plane construction should be used. on the other hand, the pcb area connected to the pin 7 (emitter of the internal switch) of the lm2574 should be kept to a minimum in order to minimize coupling to sensitive circuitry. another sensitive part of the circuit is the feedback. it is important to keep the sensitive feedback wiring short. to assure this, physically locate the programming resistors near to the regulator, when using the adjustable version of the lm2574 regulator.
lm2574 9 motorola analog ic device data pin function description pin symbol description (refer to figure 1) 5 v in this pin is the positive input supply for the lm2574 stepdown switching regulator. in order to minimize voltage transients and to supply the switching currents needed by the regulator, a suitable input bypass capacitor must be present (c in in figure 1). 7 output this is the emitter of the internal switch. the saturation voltage v sat of this output switch is typically 1.0 v. it should be kept in mind that the pcb area connected to this pin should be kept to a minimum in order to minimize coupling to sensitive circuitry. 2 sig gnd circuit signal ground pin. see the information about the printed circuit board layout. 4 pwr gnd circuit power ground pin. see the information about the printed circuit board layout. 1 feedback this pin senses regulated output voltage to complete the feedback loop. the signal is divided by the internal resistor divider network r2, r1 and applied to the noninverting input of the internal error amplifier. in the adjustable version of the lm2574 switching regulator, this pin is the direct input of the error amplifier and the resistor network r2, r1 is connected externally to allow programming of the output voltage. 3 on /off it allows the switching regulator circuit to be shut down using logic level signals, thus dropping the total input supply current to approximately 80 m a. the input threshold voltage is typically 1.5 v. applying a voltage above this value (up to +v in ) shuts the regulator off. if the voltage applied to this pin is lower than 1.5 v or if this pin is left open, the regulator will be in the aono condition. design procedure buck converter basics the lm2574 is a abucko or stepdown converter which is the most elementary forwardmode converter. its basic schematic can be seen in figure 17. the operation of this regulator topology has two distinct time periods. the first one occurs when the series switch is on, the input voltage is connected to the input of the inductor. the output of the inductor is the output voltage, and the rectifier (or catch diode) is reverse biased. during this period, since there is a constant voltage source connected across the inductor, the inductor current begins to linearly ramp upwards, as described by the following equation: i l(on) v in v out t on l during this aono period, energy is stored within the core material in the form of magnetic flux. if the inductor is properly designed, there is sufficient energy stored to carry the requirements of the load during the aoffo period. figure 17. basic buck converter d v in r load l c out power switch the next period is the aoffo period of the power switch. when the power switch turns off, the voltage across the inductor reverses its polarity and is clamped at one diode voltage drop below ground by the catch diode. current now flows through the catch diode thus maintaining the load current loop. this removes the stored energy from the inductor. the inductor current during this time is: i l(off) v out v d t off l this period ends when the power switch is once again turned on. regulation of the converter is accomplished by varying the duty cycle of the power switch. it is possible to describe the duty cycle as follows: d t on t , where t is the period of switching. for the buck converter with ideal components, the duty cycle can also be described as: d v out v in figure 18 shows the buck converter idealized waveforms of the catch diode voltage and the inductor current. figure 18. buck converter idealized waveforms power switch power switch off power switch off power switch on power switch on v on(sw) v d (fwd) time time i load (av) i min i pk diode diode power switch diode voltage inductor current
lm2574 10 motorola analog ic device data procedure (fixed output voltage version) in order to simplify the switching regulator design, a stepbystep design procedure and example is provided. procedure example given parameters: v out = regulated output voltage (3.3 v, 5.0 v, 12 v or 15 v) v in(max) = maximum input voltage i load(max) = maximum load current given parameters: v out = 5.0 v v in(max) = 15 v i load(max) = 0.4 a 1. controller ic selection according to the required input voltage, output voltage and current, select the appropriate type of the controller ic output voltage version. 1. controller ic selection according to the required input voltage, output voltage, current polarity and current value, use the lm25745 controller ic. 2. input capacitor selection (c in ) to prevent large voltage transients from appearing at the input and for stable operation of the converter, an aluminium or tantalum electrolytic bypass capacitor is needed between the input pin +v in and ground pin gnd. this capacitor should be located close to the ic using short leads. this capacitor should have a low esr (equivalent series resistance) value. 2. input capacitor selection (c in ) a 22 m f, 25 v aluminium electrolytic capacitor located near to the input and ground pins provides sufficient bypassing. 3. catch diode selection (d1) a. since the diode maximum peak current exceeds the regulator maximum load current, the catch diode current rating must be at least 1.2 times greater than the maximum load current. for a robust design the diode should have a current rating equal to the maximum current limit of the lm2574 to be able to withstand a continuous output short. b. the reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. 3. catch diode selection (d1) a . for this example the current rating of the diode is 1.0 a. b. use a 20 v 1n5817 schottky diode, or any of the suggested fast recovery diodes shown in table 1. 4. inductor selection (l1) a. according to the required working conditions, select the correct inductor value using the selection guide from figures 19 to 23. b. from the appropriate inductor selection guide, identify the inductance region intersected by the maximum input voltage line and the maximum load current line. each region is identified by an inductance value and an inductor code. c. select an appropriate inductor from the several different manufacturers part numbers listed in table 2. the designer must realize that the inductor current rating must be higher than the maximum peak current flowing through the inductor. this maximum peak current can be calculated as follows: where t on is the aono time of the power switch and for additional information about the inductor, see the inductor section in the aexternal componentso section of this data sheet. i p ( max ) i load ( max ) v in v out t on 2l t on v out v in x 1.0 f osc 4. inductor selection (l1) a. use the inductor selection guide shown in figure 20. b. from the selection guide, the inductance area intersected by the 15 v line and 0.4 a line is 330. c. inductor value required is 330 m h. from table 2, choose an inductor from any of the listed manufacturers.
lm2574 11 motorola analog ic device data procedure (fixed output voltage version) (continued) in order to simplify the switching regulator design, a stepbystep design procedure and example is provided. procedure example 5. output capacitor selection (c out ) a. since the lm2574 is a forwardmode switching regulator with voltage mode control, its open loop 2pole1zero frequency characteristic has the dominant polepair determined by the output capacitor and inductor values. for stable operation and an acceptable ripple voltage, (approximately 1% of the output voltage) a value between 100 m f and 470 m f is recommended. b. due to the fact that the higher voltage electrolytic capacitors generally have lower esr (equivalent series resistance) numbers, the output capacitor's voltage rating should be at least 1.5 times greater than the output voltage. for a 5.0 v regulator, a rating at least 8.0 v is appropriate, and a 10 v or 16 v rating is recommended. 5. output capacitor selection (c out ) a. c out = 100 m f to 470 m f standard aluminium electrolytic. b. capacitor voltage rating = 20 v. procedure (adjustable output version: lm2574adj) procedure example given parameters: v out = regulated output voltage v in(max) = maximum dc input voltage i load(max) = maximum load current given parameters: v out = 24 v v in(max) = 40 v i load(max) = 0.4 a 1. programming output voltage to select the right programming resistor r1 and r2 value (see figure 2) use the following formula: where v ref = 1.23 v resistor r1 can be between 1.0 k w and 5.0 k w . (for best temperature coefficient and stability with time, use 1% metal film resistors). v out v ref 1.0 r2 r1 r2 r1 v out v ref 1.0 1. programming output voltage ( selecting r1 and r2) select r1 and r2 : v out = 1.23 select r1 = 1.0 k w r2 = 18.51 k w , choose a 18.7 k w metal film resistor. 1.0 r2 r1 r2 r1 v out v ref 1.0 1.0 k 10 v 1.23 v 1.0 2. input capacitor selection (c in ) to prevent large voltage transients from appearing at the input and for stable operation of the converter, an aluminium or tantalum electrolytic bypass capacitor is needed between the input pin +v in and ground pin gnd. this capacitor should be located close to the ic using short leads. this capacitor should have a low esr (equivalent series resistance) value. for additional information see input capacitor section in the aexternal componentso section of this data sheet. 2. input capacitor selection (c in ) a 22 m f aluminium electrolytic capacitor located near the input and ground pin provides sufficient bypassing. 3. catch diode selection (d1) a. since the diode maximum peak current exceeds the regulator maximum load current the catch diode current rating must be at least 1.2 times greater than the maximum load current. for a robust design, the diode should have a current rating equal to the maximum current limit of the lm2574 to be able to withstand a continuous output short. b. the reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. 3. catch diode selection (d1) a. for this example, a 1.0 a current rating is adequate. b. use a 50 v mbr150 schottky diode or any suggested fast recovery diodes in table 1.
lm2574 12 motorola analog ic device data procedure (adjustable output version: lm2574adj) procedure example 4. inductor selection (l1) a. use the following formula to calculate the inductor volt x microsecond [v x m s] constant: b. match the calculated e x t value with the corresponding number on the vertical axis of the inductor value selection guide shown in figure 23. this e x t constant is a measure of the energy handling capability of an inductor and is dependent upon the type of core, the core area, the number of turns, and the duty cycle. c. next step is to identify the inductance region intersected by the e x t value and the maximum load current value on the horizontal axis shown in figure 27. d. from the inductor code, identify the inductor value. then select an appropriate inductor from table 2. the inductor chosen must be rated for a switching frequency of 52 khz and for a current rating of 1.15 x i load . the inductor current rating can also be determined by calculating the inductor peak current: where t on is the aono time of the power switch and for additional information about the inductor, see the inductor section in the aexternal componentso section of this data sheet. t on v out v in x 1.0 f osc i p ( max ) i load ( max ) v in v out t on 2l ext (v in v out ) v out v in x 10 6 f [ hz ] vx s 4. inductor selection (l1) a. b. c. i load(max) = 0.4 a inductance region = 1000 d. proper inductor value = 1000 m h choose the inductor from table 2. ext (40 24) x 24 40 x 1000 52 105 vx s ext 185 vx s calculate e x t vx s constant : 5. output capacitor selection (c out ) a. since the lm2574 is a forwardmode switching regulator with voltage mode control, its open loop 2pole1zero frequency characteristic has the dominant polepair determined by the output capacitor and inductor values. for stable operation, the capacitor must satisfy the following requirement: b. capacitor values between 10 m f and 2000 m f will satisfy the loop requirements for stable operation. to achieve an acceptable output ripple voltage and transient response, the output capacitor may need to be several times larger than the above formula yields. c. due to the fact that the higher voltage electrolytic capacitors generally have lower esr (equivalent series resistance) numbers, the output capacitor's voltage rating should be at least 1.5 times greater than the output voltage. for a 5.0 v regulator, a rating of at least 8.0 v is appropriate, and a 10 v or 16v rating is recommended. c out 13, 300 v in ( max ) v out xl h f 5. output capacitor selection (c out ) a. to achieve an acceptable ripple voltage, select c out = 100 m f electrolytic capacitor. c out 13, 300 x 40 24 x 1000 22.2 f
lm2574 13 motorola analog ic device data et, voltage time (v s) m v in , maximum input voltage (v) v in , maximum input voltage (v) v in , maximum input voltage (v) v in , maximum input voltage (v) i l , maximum load current (a) i l , maximum load current (a) i l , maximum load current (a) i l , maximum load current (a) figure 19. lm25743.3 i l , maximum load current (a) figure 20. lm25745 680 figure 21. lm257412 figure 22. lm257415 figure 23. lm2574adj 150 470 220 100 330 1000 330 680 470 150 220 2200 470 1500 1000 330 680 220 2200 470 1500 1000 680 2200 470 1500 1000 330 680 220 150 100 68 lm2574 series buck regulator design procedures (continued) indicator value selection guide (for continuous mode operation) 60 20 15 12 10 9.0 8.0 7.0 6.0 5.0 60 30 20 15 12 10 9.0 8.0 7.0 60 40 30 25 20 18 17 16 15 14 60 40 30 25 22 20 19 18 17 250 200 150 100 80 60 50 40 30 20 15 10 0.5 0.4 0.3 0.2 0.15 0.1 0.5 0.4 0.3 0.2 0.15 0.1 0.5 0.4 0.3 0.2 0.15 0.1 0.5 0.4 0.3 0.2 0.15 0.1 0.5 0.4 0.3 0.2 0.15 0.1 330 220
lm2574 14 motorola analog ic device data table 1. diode selection guide gives an overview about throughhole diodes for an effective design. device listed in bold are available from motorola v r 1.0 amp diodes v r schottky fast recovery 20 v 1n5817 mbr120p 30 v 1n5818 mbr130p mur110 40 v 1n5819 mbr140p mur110 (rated to 100 v) 50 v mbr150 60 v mbr160 table 2. inductor selection guide inductor value pulse engineering tech 39 renco npi 68 m h * 55 258 sn rl128468 np5915 100 m h * 55 308 sn rl1284100 np5916 150 m h 52625 55 356 sn rl1284150 np5917 220 m h 52626 55 406 sn rl1284220 np5918/5919 330 m h 52627 55 454 sn rl1284330 np5920/5921 470 m h 52628 * rl1284470 np5922 680 m h 52629 55 504 sn rl1284680 np5923 1000 m h 52631 55 554 sn rl12841000 * 1500 m h * * rl12841500 * 2200 m h * * rl12842200 * * : contact manufacturer table 3. example of several inductor manufacturers phone/fax numbers pulse engineering inc. phone fax + 16196748100 + 16196748262 pulse engineering inc. europe phone fax + 3539324107 + 3539324459 renco electronics inc. phone fax + 15166455828 + 15165865562 tech 39 phone fax + 33141151681 + 33147095051 npi/apc phone fax + 44634290588
lm2574 15 motorola analog ic device data external components input capacitor (c in ) the input capacitor should have a low esr for stable operation of the switch mode converter a low esr (equivalent series resistance) aluminium or solid tantalum bypass capacitor is needed between the input pin and the ground pin, to prevent large voltage transients from appearing at the input. it must be located near the regulator and use short leads. with most electrolytic capacitors, the capacitance value decreases and the esr increases with lower temperatures. for reliable operation in temperatures below 25 c larger values of the input capacitor may be needed. also paralleling a ceramic or solid tantalum capacitor will increase the regulator stability at cold temperatures. rms current rating of c in the important parameter of the input capacitor is the rms current rating. capacitors that are physically large and have large surface area will typically have higher rms current ratings. for a given capacitor value, a higher voltage electrolytic capacitor will be physically larger than a lower voltage capacitor, and thus be able to dissipate more heat to the surrounding air, and therefore will have a higher rms current rating. the consequences of operating an electrolytic capacitor beyond the rms current rating is a shortened operating life. in order to assure maximum capacitor operating lifetime, the capacitor's rms ripple current rating should be: i rms 1.2 x d x i load where d is the duty cycle, for a continuous mode buck regulator d t on t v out v in and d t on t |v out | |v out | v in for a buckboost regulator. output capacitor (c out ) for low output ripple voltage and good stability, low esr output capacitors are recommended. an output capacitor has two main functions: it filters the output and provides regulator loop stability. the esr of the output capacitor and the peaktopeak value of the inductor ripple current are the main factors contributing to the output ripple voltage value. standard aluminium electrolytics could be adequate for some applications but for quality design, low esr types are recommended. an aluminium electrolytic capacitor's esr value is related to many factors, such as the capacitance value, the voltage rating, the physical size and the type of construction. in most cases, the higher voltage electrolytic capacitors have lower esr value. often capacitors with much higher voltage ratings may be needed to provide low esr values, that are required for low output ripple voltage. the output capacitor requires an esr value that has an upper and lower limit as mentioned above, a low esr value is needed for low output ripple voltage, typically 1% to 2% of the output voltage. but if the selected capacitor's esr is extremely low (below 0.03 w ), there is a possibility of an unstable feedback loop, resulting in oscillation at the output. this situation can occur when a tantalum capacitor, that can have a very low esr, is used as the only output capacitor. at low temperatures, put in parallel aluminium electrolytic capacitors with tantalum capacitors electrolytic capacitors are not recommended for temperatures below 25 c. the esr rises dramatically at cold temperatures and typically rises 3 times at 25 c and as much as 10 times at 40 c. solid tantalum capacitors have much better esr spec at cold temperatures and are recommended for temperatures below 25 c. they can be also used in parallel with aluminium electrolytics. the value of the tantalum capacitor should be about 10% or 20% of the total capacitance. the output capacitor should have at least 50% higher rms ripple current rating at 52 khz than the peaktopeak inductor ripple current. catch diode locate the catch diode close to the lm2574 the lm2574 is a stepdown buck converter, it requires a fast diode to provide a return path for the inductor current when the switch turns off. this diode must be located close to the lm2574 using short leads and short printed circuit traces to avoid emi problems. use a schottky or a soft switching ultrafast recovery diode since the rectifier diodes are very significant source of losses within switching power supplies, choosing the rectifier that best fits into the converter design is an important process. schottky diodes provide the best performance because of their fast switching speed and low forward voltage drop. they provide the best efficiency especially in low output voltage applications (5.0 v and lower). another choice could be fastrecovery, or ultrafast recovery diodes. it has to be noted, that some types of these diodes with an abrupt turnoff characteristic may cause instability or emi troubles. a fastrecovery diode with soft recovery characteristics can better fulfill some quality, low noise design requirements. table 1 provides a list of suitable diodes for the lm2574 regulator. standard 50/60 hz rectifier diodes, such as the 1n4001 series or 1n5400 series are not suitable. inductor the magnetic components are the cornerstone of all switching power supply designs. the style of the core and the winding technique used in the magnetic component's design have a great influence on the reliability of the overall power supply. using an improper or poorly designed inductor can cause high voltage spikes generated by the rate of transitions in current within the switching power supply, and the possibility of core saturation can arise during an abnormal operational mode. voltage spikes can cause the semiconductors to enter avalanche breakdown and the part can instantly fail if enough energy is applied. it can also cause significant rfi (radio frequency interference) and emi (electromagnetic interference) problems.
lm2574 16 motorola analog ic device data continuous and discontinuous mode of operation. the lm2574 stepdown converter can operate in both the continuous and the discontinuous modes of operation. the regulator works in the continuous mode when loads are relatively heavy, the current flows through the inductor continuously and never falls to zero. under light load conditions, the circuit will be forced to the discontinuous mode when inductor current falls to zero for certain period of time (see figure 24 and figure 25). each mode has distinctively different operating characteristics, which can affect the regulator performance and requirements. in many cases the preferred mode of operation is the continuous mode. it offers greater output power, lower peak currents in the switch, inductor and diode, and can have a lower output ripple voltage. on the other hand it does require larger inductor values to keep the inductor current flowing continuously, especially at low output load currents and/or high input voltages. to simplify the inductor selection process, an inductor selection guide for the lm2574 regulator was added to this data sheet (figures 19 through 23). this guide assumes that the regulator is operating in the continuous mode, and selects an inductor that will allow a peaktopeak inductor ripple current to be a certain percentage of the maximum design load current. this percentage is allowed to change as different design load currents are selected. for light loads (less than approximately 0.2 a) it may be desirable to operate the regulator in the discontinuous mode, because the inductor value and size can be kept relatively low. consequently, the percentage of inductor peaktopeak current increases. this discontinuous mode of operation is perfectly acceptable for this type of switching converter. any buck regulator will be forced to enter discontinuous mode if the load current is light enough. selecting the right inductor style some important considerations when selecting a core type are core material, cost, the output power of the power supply, the physical volume the inductor must fit within, and the amount of emi (electromagnetic interference) shielding that the core must provide. there are many different styles of inductors available, such as pot core, ecore, toroid and bobbin core, as well as different core materials such as ferrites and powdered iron from different manufacturers. for high quality design regulators the toroid core seems to be the best choice. since the magnetic flux is contained within the core, it generates less emi, reducing noise problems in sensitive circuits. the least expensive is the bobbin core type, which consists of wire wound on a ferrite rod core. this type of inductor generates more emi due to the fact that its core is open, and the magnetic flux is not contained within the core. when multiple switching regulators are located on the same printed circuit board, open core magnetics can cause interference between two or more of the regulator circuits, especially at high currents due to mutual coupling. a toroid, pot core or ecore (closed magnetic structure) should be used in such applications. do not operate an inductor beyond its maximum rated current exceeding an inductor's maximum current rating may cause the inductor to overheat because of the copper wire losses, or the core may saturate. core saturation occurs when the flux density is too high and consequently the cross sectional area of the core can no longer support additional lines of magnetic flux. this causes the permeability of the core to drop, the inductance value decreases rapidly and the inductor begins to look mainly resistive. it has only the dc resistance of the winding. this can cause the switch current to rise very rapidly and force the lm2574 internal switch into cyclebycycle current limit, thus reducing the dc output load current. this can also result in overheating of the inductor and/or the lm2574. different inductor types have different saturation characteristics, and this should be kept in mind when selecting an inductor. horizontal time base: 5.0 m s/div vertrical resolution 200 madv figure 24. continuous mode switching current waveforms 0.5 a 0 a 0.5 a 0 a power switch current waveform inductor current waveform vertical resolution 100 madv horizontal time base: 5.0 m s/div figure 25. continuous mode switching current waveforms 0.1 a 0 a 0.1 a 0 a power switch current waveform inductor current waveform
lm2574 17 motorola analog ic device data general recommendations output voltage ripple and transients source of the output ripple since the lm2574 is a switch mode power supply regulator, its output voltage, if left unfiltered, will contain a sawtooth ripple voltage at the switching frequency. the output ripple voltage value ranges from 0.5% to 3% of the output voltage. it is caused mainly by the inductor sawtooth ripple current multiplied by the esr of the output capacitor. short voltage spikes and how to reduce them the regulator output voltage may also contain short voltage spikes at the peaks of the sawtooth waveform (see figure 26). these voltage spikes are present because of the fast switching action of the output switch, and the parasitic inductance of the output filter capacitor. there are some other important factors such as wiring inductance, stray capacitance, as well as the scope probe used to evaluate these transients, all these contribute to the amplitude of these spikes. to minimize these voltage spikes, low inductance capacitors should be used, and their lead lengths must be kept short. the importance of quality printed circuit board layout design should also be highlighted. horizontal time base: 5.0 m s/div vertrical resolution 20 mv/div voltage spikes caused by switching action of the output switch and the parasitic inductance of the output capacitor figure 26. output ripple voltage waveforms unfiltered output voltage filtered output voltage minimizing the output ripple in order to minimize the output ripple voltage it is possible to enlarge the inductance value of the inductor l1 and/or to use a larger value output capacitor. there is also another way to smooth the output by means of an additional lc filter (20 m h, 100 m f), that can be added to the output (see figure 35) to further reduce the amount of output ripple and transients. with such a filter it is possible to reduce the output ripple voltage transients 10 times or more. figure 26 shows the difference between filtered and unfiltered output waveforms of the regulator shown in figure 34. the upper waveform is from the normal unfiltered output of the converter, while the lower waveform shows the output ripple voltage filtered by an additional lc filter. heatsinking and thermal considerations the lm2574 is available in both 8pin dip and so16l packages. when used in the typical application the copper lead frame conducts the majority of the heat from the die, through the leads, to the printed circuit copper. the copper and the board are the heatsink for this package and the other heat producing components, such as the catch diode and inductor. for the best thermal performance, wide copper traces should be used and all ground and unused pins should be soldered to generous amounts of printed circuit board copper, such as a ground plane. large areas of copper provide the best transfer of heat to the surrounding air. one exception to this is the output (switch) pin, which should not have large areas of copper in order to minimize coupling to sensitive circuitry. additional improvement in heat dissipation can be achieved even by using of double sided or multilayer boards which can provide even better heat path to the ambient. using a socket for the 8pin dip package is not recommended because socket represents an additional thermal resistance, and as a result the junction temperature will be higher. since the current rating of the lm2574 is only 0.5 a, the total package power dissipation for this switcher is quite low, ranging from approximately 0.1 w up to 0.75 w under varying conditions. in a carefully engineered printed circuit board, the throughhole dip package can easily dissipate up to 0.75 w, even at ambient temperatures of 60 c, and still keep the maximum junction temperature below 125 c. thermal analysis and design the following procedure must be performed to determine the operating junction temperature. first determine: 1. p d(max) maximum regulator power dissipation in the application. 2. t a(max) maximum ambient temperature in the application. 3. t j(max) maximum allowed junction temperature (125 c for the lm2574). for a conservative design, the maximum junction temperature should not exceed 110 c to assure safe operation. for every additional +10 c temperature rise that the junction must withstand, the estimated operating lifetime of the component is halved. 4. r q jc package thermal resistance junctioncase. 5. r q ja package thermal resistance junctionambient. (refer to absolute maximum ratings on page 2 of this data sheet or r q jc and r q ja values). the following formula is to calculate the approximate total power dissipated by the lm2574: p d = (v in x i q ) + d x i load x v sat where d is the duty cycle and for buck converter d t on t v o v in , i q (quiescent current) and v sat can be found in the lm2574 data sheet, v in is minimum input voltage applied, v o is the regulator output voltage, i load is the load current.
lm2574 18 motorola analog ic device data d1 mbr150 l1 68 m h output 7 1 feedback 8.0 to 25 v unregulated dc input c in 22 m f 5 3 4on /off pwr gnd +v in 12 v @ 100 ma regulated output c out 680 m f lm257412 2 sig gnd figure 27. inverting buckboost develops 12 v the dynamic switching losses during turnon and turnoff can be neglected if a proper type catch diode is used. the junction temperature can be determined by the following expression: t j = (r q ja )(p d ) + t a where (r q ja )(p d ) represents the junction temperature rise caused by the dissipated power and t a is the maximum ambient temperature. some aspects that can influence thermal design it should be noted that the package thermal resistance and the junction temperature rise numbers are all approximate, and there are many factors that will affect these numbers, such as pc board size, shape, thickness, physical position, location, board temperature, as well as whether the surrounding air is moving or still. at higher power levels the thermal resistance decreases due to the increased air current activity. other factors are trace width, total printed circuit copper area, copper thickness, single or doublesided, multilayer board, the amount of solder on the board or even color of the traces. the size, quantity and spacing of other components on the board can also influence its effectiveness to dissipate the heat. some of them, like the catch diode or the inductor will generate some additional heat. additional applications inverting regulator an inverting buckboost regulator using the lm257412 is shown in figure 27. this circuit converts a positive input voltage to a negative output voltage with a common ground by bootstrapping the regulators ground to the negative output voltage. by grounding the feedback pin, the regulator senses the inverted output voltage and regulates it. in this example the lm257412 is used to generate a 12 v output. the maximum input voltage in this case cannot exceed 28 v because the maximum voltage appearing across the regulator is the absolute sum of the input and output voltages and this must be limited to a maximum of 40 v. this circuit configuration is able to deliver approximately 0.1 a to the output when the input voltage is 8.0 v or higher. at lighter loads the minimum input voltage required drops to approximately 4.7 v, because the buckboost regulator topology can produce an output voltage that, in its absolute value, is either greater or less than the input voltage. since the switch currents in this buckboost configuration are higher than in the standard buck converter topology, the available output current is lower. this type of buckboost inverting regulator can also require a larger amount of startup input current, even for light loads. this may overload an input power source with a current limit less than 0.6 a. because of the relatively high startup currents required by this inverting regulator topology, the use of a delayed startup or an undervoltage lockout circuit is recommended. while using a delayed startup arrangement, the input capacitor can charge up to a higher voltage before the switchmode regulator begins to operate. the high input current needed for startup is now partially supplied by the input capacitor c in . design recommendations: the inverting regulator operates in a different manner than the buck converter and so a different design procedure has to be used to select the inductor l1 or the output capacitor c out . the output capacitor values must be larger than what is normally required for buck converter designs. low input voltages or high output currents require a large value output capacitor (in the range of thousands of m f). the recommended range of inductor values for the inverting converter design is between 68 m h and 220 m h. to select an inductor with an appropriate current rating, the inductor peak current has to be calculated. d1 mbr150 l1 68 m h output 7 1 feedback 12 to 25 v unregulated dc input c in 22 m f /50 v 5 4 3on /off pwr gnd +v in 12 v @ 100 ma regulated output c out 680 m f /16 v lm257412 c1 0.1 m f r1 47 k r2 47 k 2 sig gnd figure 28. inverting buckboost regulator with delayed startup the following formula is used to obtain the peak inductor current: i peak i load v in |v o | v in v in xt on 2l 1 where t on |v o | v in |v o | x 1.0 f osc , and f osc = 52 khz. under normal continuous inductor current operating conditions, the worst case occurs when v in is minimal. it has been already mentioned above, that in some situations, the delayed startup or the undervoltage lockout features could be very useful. a delayed startup circuit
lm2574 19 motorola analog ic device data applied to a buckboost converter is shown in figure 28. figure 34 in the aundervoltage lockouto section describes an undervoltage lockout feature for the same converter topology. with the inverting configuration, the use of the on /off pin requires some level shifting techniques. this is caused by the fact, that the ground pin of the converter ic is no longer at ground. now, the on /off pin threshold voltage (1.3 v approximately) has to be related to the negative output voltage level. there are many different possible shutdown methods, two of them are shown in figures 29 and 30. lm2574xx 5 2 and 4 3 gnds pins on /off +v in r2 47 k c in 22 m f note : this picture does not show the complete circuit. r1 47 k r3 470 shutdown input moc8101 v out off on 5.0 v 0 +v in figure 29. inverting buckboost regulator shutdown circuit using an optocoupler note : this picture does not show the complete circuit. r2 5.6 k q1 2n3906 lm2574xx 5 2 and 4 3 gnds pins on /off r1 12 k v out +v in shutdown input off on +v 0 +v in c in 22 m f figure 30. inverting buckboost regulator shutdown circuit using a pnp transistor negative boost regulator this example is a variation of the buckboost topology and it is called negative boost regulator. this regulator experiences relatively high switch current, especially at low input voltages. the internal switch current limiting results in lower output load current capability. the circuit in figure 31 shows the negative boost configuration. the input voltage in this application ranges from 5.0 to 12 v and provides a regulated 12 v output. if the input voltage is greater than 12 v, the output will rise above 12 v accordingly, but will not damage the regulator. 1n5817 330 m h output 7 1 feedback v out = 12 v load current 60 ma for v in = 5.2 v 120 ma for v in = 7.0 v v in l1 d1 c out 1000 m f c in 22 m f lm257412 5 3 4 on /off pwr gnd +v in 2 sig gnd 5.0 to 12 v figure 31. negative boost regulator design recommendations: the same design rules as for the previous inverting buckboost converter can be applied. the output capacitor c out must be chosen larger than what would be required for a standard buck converter. low input voltages or high output currents require a large value output capacitor (in the range of thousands of m f). the recommended range of inductor values for the negative boost regulator is the same as for inverting converter design. another important point is that these negative boost converters cannot provide any current limiting load protection in the event of a short in the output so some other means, such as a fuse, may be necessary to provide the load protection. delayed startup there are some applications, like the inverting regulator already mentioned above, which require a higher amount of startup current. in such cases, if the input power source is limited, this delayed startup feature becomes very useful. to provide a time delay between the time when the input voltage is applied and the time when the output voltage comes up, the circuit in figure 32 can be used. as the input voltage is applied, the capacitor c1 charges up, and the voltage across the resistor r2 falls down. when the voltage on the on /off pin falls below the threshold value 1.3 v, the regulator starts up. resistor r1 is included to limit the maximum voltage applied to the on /off pin. it reduces the power supply noise sensitivity, and also limits the capacitor c1 discharge current, but its use is not mandatory. when a high 50 hz or 60 hz (100 hz or 120 hz respectively) ripple voltage exists, a long delay time can cause some problems by coupling the ripple into the on /off pin, the regulator could be switched periodically on and off with the line (or double) frequency.
lm2574 20 motorola analog ic device data r1 47 k lm2574xx 5 2 and 4 3 gnds pins on /off r2 47 k +v in +v in c1 0.1 m f c in 22 m f note : this picture does not show the complete circuit. figure 32. delayed startup circuitry undervoltage lockout some applications require the regulator to remain off until the input voltage reaches a certain threshold level. figure 33 shows an undervoltage lockout circuit applied to a buck regulator. a version of this circuit for buckboost converter is shown in figure 34. resistor r3 pulls the on /off pin high and keeps the regulator off until the input voltage reaches a predetermined threshold level, which is determined by the following expression: v th v z1 1.0 r2 r1 v be ( q1 ) r1 10 k z1 1n5242b r2 10 k q1 2n3904 r3 47 k c in 22 m f lm2574xx 5 2 and 4 3 gnds pins on /off +v in +v in note : this picture does not show the complete circuit. figure 33. undervoltage lockout circuit for buck converter r2 15 k z1 1n5242 r1 15 k q1 2n3904 r3 68 k c in 22 m f lm2574xx 5 2 and 4 3 gnds pins on /off +v in +v in v out note : this picture does not show the complete circuit (see figure 27). figure 34. undervoltage lockout circuit for buckboost converter adjustable output, lowripple power supply a 0.5 a output current capability power supply that features an adjustable output voltage is shown in figure 35. this regulator delivers 0.5 a into 1.2 to 35 v output. the input voltage ranges from roughly 3.0 to 40 v. in order to achieve a 10 or more times reduction of output ripple, an additional lc filter is included in this circuit.
lm2574 21 motorola analog ic device data d1 1n5819 l1 150 m h output 7 1 feedback r2 50 k r1 1.1 k l2 20 m h output voltage 1.2 to 35 v @ 0.5 a optional output ripple filter 40 v max unregulated dc input c out 1000 m f c1 100 m f c in 22 m f lm2574adj 5 3 4on /off pwr gnd +v in 2 sig gnd figure 35. 1.2 to 35 v adjustable 500 ma power supply with low output ripple the lm25745 stepdown voltage regulator with 5.0 v @ 0.5 a output power capability. typical application with throughhole pc board layout d1 1n5819 l1 330 m h output 7 1 feedback unregulated dc input +v in = 7.0 to 40 v c2 220 m f c1 22 m f lm25745 5 3 4on /off pwr gnd +v in regulated output +v out = 5.0 v @ 0.5 a gnd gnd c1 22 m f, 63 v, aluminium electrolytic c2 220 m f, 16 v, aluminium electrolytic d1 1.0 a, 40 v, schottky rectifier, 1n5819 l1 330 m h, rl1284330, renco electronics 2 sig gnd figure 36. schematic diagram of the lm25745 stepdown converter lm25745.0 c1 c2 + + u1 l1 d1 v out gnd gnd +v in figure 37. pc board layout component side note : not to scale. figure 38. pc board layout copper side note : not to scale.
lm2574 22 motorola analog ic device data the lm2574adj stepdown voltage regulator with 5.0 v @ 0.5 a output power capability typical application with throughhole pc board layout d1 1n5819 l1 330 m h output 7 1 feedback r2 6.12 k w r1 2.0 k w l2 22 m h regulated output filtered v out = 5.0 v @ 0.5 a output ripple filter unregulated dc input c2 220 m f c3 100 m f c1 22 m f lm2574adj 5 3 4on /off pwr gnd +v in 2 sig gnd +v in = 7.0 to 40 v gnd gnd c1 22 m f, 63 v, aluminium electrolytic c2 220 m f, 16 v, aluminium electrolytic c3 100 m f, 16 v aluminium electrolytic d1 1.0 a, 40 v, schottky rectifier, 1n5819 l1 330 m h, rl1284330, renco electronics l2 25 m h, sft52501, tdk r1 2.0 k w , 0.1%, 0.25 w r2 6.12 k w , 0.1%, 0.25 w figure 39. schematic diagram of the 5.0 v @ 0.5 a stepdown converter using the lm2574adj (an additional lc filter is included to achieve low output ripple voltage) lm2574 c1 c2 + + u1 l1 d1 v out gnd +v in c3 + gnd l2 r1 r2 figure 40. pc board layout component side note : not to scale. figure 41. pc board layout copper side note : not to scale. references ? national semiconductor lm2574 data sheet and application note ? national semiconductor lm2594 data sheet and application note ? marty brown apractical switching power supply designo, academic press, inc., san diego 1990 ? ray ridley ahigh frequency magnetics designo, ridley engineering, inc. 1995
lm2574 23 motorola analog ic device data n suffix plastic package case 62605 (dip8) issue k outline dimensions notes: 1. dimension l to center of lead when formed parallel. 2. package contour optional (round or square corners). 3. dimensioning and tolerancing per ansi y14.5m, 1982. style 1: pin 1. ac in 2. dc + in 3. dc in 4. ac in 5. ground 6. output 7. auxiliary 8. v cc 14 5 8 f note 2 a b t seating plane h j g d k n c l m m a m 0.13 (0.005) b m t dim min max min max inches millimeters a 9.40 10.16 0.370 0.400 b 6.10 6.60 0.240 0.260 c 3.94 4.45 0.155 0.175 d 0.38 0.51 0.015 0.020 f 1.02 1.78 0.040 0.070 g 2.54 bsc 0.100 bsc h 0.76 1.27 0.030 0.050 j 0.20 0.30 0.008 0.012 k 2.92 3.43 0.115 0.135 l 7.62 bsc 0.300 bsc m 10 10 n 0.76 1.01 0.030 0.040 dw suffix plastic package case 751g03 (so16l) issue b d 14x b 16x seating plane s a m 0.25 b s t 16 9 8 1 h x 45 m b m 0.25 h 8x e b a e t a1 a l c notes: 1. dimensions are in millimeters. 2. interpret dimensions and tolerances per asme y14.5m, 1994. 3. dimensions d and e do not inlcude mold protrusion. 4. maximum mold protrusion 0.15 per side. 5. dimension b does not include dambar protrusion. allowable dambar protrusion shall be 0.13 total in excess of the b dimension at maximum material condition. dim min max millimeters a 2.35 2.65 a1 0.10 0.25 b 0.35 0.49 c 0.23 0.32 d 10.15 10.45 e 7.40 7.60 e 1.27 bsc h 10.05 10.55 h 0.25 0.75 l 0.50 0.90 0 7
lm2574 24 motorola analog ic device data motorola reserves the right to make changes without further notice to any products herein. motorola makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does motorola assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation consequential or incidental damages. atypicalo parameters which may be provided in motorola data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. all operating parameters, including atypicalso must be validated for each customer application by customer's technical experts. motorola does not convey any license under its patent rights nor the rights of others. motorola products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the motorola product could create a situation where personal injury or death may occur. should buyer purchase or use motorola products for any such unintended or unauthorized application, buyer shall indemnify and hold motorola and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that motorola was negligent regarding the design or manufacture of the part. motorola and are registered trademarks of motorola, inc. motorola, inc. is an equal opportunity/affirmative action employer. mfax is a trademark of motorola, inc. how to reach us: usa / europe / locations not listed : motorola literature distribution; japan : nippon motorola ltd.; spd, strategic planning office, 141, p.o. box 5405, denver, colorado 80217. 13036752140 or 18004412447 4321 nishigotanda, shinagawaku, tokyo, japan. 81354878488 customer focus center: 18005216274 mfax ? : rmfax0@email.sps.mot.com touchtone 1 6022446609 asia / pacific : motorola semiconductors h.k. ltd.; 8b tai ping industrial park, motorola fax back system us & canada only 18007741848 51 ting kok road, tai po, n.t., hong kong. 85226629298 http://sps.motorola.com/mfax/ home page : http://motorola.com/sps/ lm2574/d ?

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