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device operating temperature range package easy switcher ? 1.0 a stepdown voltage regulator ordering information lm2575t** lm2575tv** t j = 40 to +125 c straight lead vertical mount device type/nominal output voltage lm25753.3 lm25755 lm257512 lm257515 lm2575adj 3.3 v 5.0 v 12 v 15 v 1.23 v to 37 v d2t suffix plastic package case 936a (d 2 pak) 1 5 order this document by lm2575/d t suffix plastic package case 314d tv suffix plastic package case 314b pin 1. v in 2. output 3. ground 4. feedback 5. on /off lm2575d2t** surface mount 1 5 1 5 heatsink surface (shown as terminal 6 in case outline drawing) is connected to pin 3. heatsink surface connected to pin 3. ** = voltage option, ie. 3.3, 5.0, 12, 15 v and ** =\ adjustable output. semiconductor technical data 1 motorola analog ic device data ?
the lm2575 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 1.0 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 optimised for use with the lm2575 are offered by several different inductor manufacturers. since the lm2575 converter is a switchmode power supply, its efficiency is significantly higher in comparison with popular threeterminal linear regulators, especially with higher input voltages. in many cases, the power dissipated by the lm2575 regulator is so low, that no heatsink is required or its size could be reduced dramatically. the lm2575 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 80 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 of 1.23 v to 37 v 4% maximum over line and load conditions ? guaranteed 1.0 a output current ? wide input voltage range: 4.75 v 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
lm2575 2 motorola analog ic device data figure 1. block diagram and typical application 7.0 v 40 v unregulated dc input l1 330 m h gnd +v in 1 c in 100 m f 3on /off 5 output 2 feedback 4 d1 1n5819 c out 330 m f typical application (fixed output voltage versions) representative block diagram and typical application unregulated dc input +v in 1 c out feedback 4 c in l1 d1 r2 r1 1.0 k output 2 gnd 3 on /off 5 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 regulated output 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 lm2575 5.0 v regulated output 1.0 a load this device contains 162 active transistors. 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 (steadystate) 1.0 v power dissipation case 314b and 314d (to220, 5lead) p d internally limited w thermal resistance, junctiontoambient r q ja 65 c/w thermal resistance, junctiontocase r q jc 5.0 c/w case 936a (d 2 pak) p d internally limited w thermal resistance, junctiontoambient (figure 34) r q ja 70 c/w thermal resistance, junctiontocase r q jc 5.0 c/w storage temperature range t stg 65 to +150 c minimum esd rating (human body model: c = 100 pf, r = 1.5 k w ) 3.0 kv lead temperature (soldering, 10 s) 260 c maximum junction temperature t j 150 c note: esd data available upon request.
lm2575 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 14) 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, and v in = 30 v for the 15 v version. i load = 200 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.) characteristics symbol min typ max unit lm25753.3 ([note 1] test circuit figure 14) output voltage (v in = 12 v, i load = 0.2 a, t j = 25 c) v out 3.234 3.3 3.366 v output voltage (4.75 v v in 40 v, 0.2 a i load 1.0 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 = 1.0 a) h 75 % lm25755 ([note 1] test circuit figure 14) output voltage (v in = 12 v, i load = 0.2 a, t j = 25 c) v out 4.9 5.0 5.1 v output voltage (8.0 v v in 40 v, 0.2 a i load 1.0 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 = 1.0 a) h 77 % lm257512 ([note 1] test circuit figure 14) output voltage (v in = 25 v, i load = 0.2 a, t j = 25 c) v out 11.76 12 12.24 v output voltage (15 v v in 40 v, 0.2 a i load 1.0 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 = 15v, i load = 1.0 a) h 88 % lm257515 ([note 1] test circuit figure 14) output voltage (v in = 30 v, i load = 0.2 a, t j = 25 c) v out 14.7 15 15.3 v output voltage (18 v v in 40 v, 0.2 a i load 1.0 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 = 1.0 a) h 88 % lm2575 adjustable version ([note 1] test circuit figure 14) feedback voltage (v in = 12 v, i load = 0.2 a, v out = 5.0 v, t j = 25 c) v fb 1.217 1.23 1.243 v feedback voltage (8.0 v v in 40 v, 0.2 a i load 1.0 a, v out = 5.0 v) v fb 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 = 1.0 a, v out = 5.0 v) h 77 % notes: 1. external components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. when the lm2575 is used as shown in the figure 14 test circuit, system performance will be as shown in system parameters section . 2. tested junction temperature range for the lm2575: t low = 40 c t high = +125 c
lm2575 4 motorola analog ic device data device parameters 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, and v in = 30 v for the 15 v version. i load = 200 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.) characteristics symbol min typ max unit 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 osc khz t j = 25 c 52 t j = 0 to +125 c 47 58 t j = 40 to +125 c 42 63 saturation voltage (i out = 1.0 a [note 4]) v sat v t j = 25 c 1.0 1.2 t j = 40 to +125 c 1.3 max duty cycle (aono) [note 5] dc 94 98 % current limit (peak current [notes 4 and 3]) i cl a t j = 25 c 1.7 2.3 3.0 t j = 40 to +125 c 1.4 3.2 output leakage current [notes 6 and 7], t j = 25 c i l ma output = 0 v 0.8 2.0 output = 1.0 v 6.0 20 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 80 200 t j = 40 to +125 c 400 on /off pin logic input level (test circuit figure 14) v v out = 0 v v ih t j = 25 c 2.2 1.4 t j = 40 to +125 c 2.4 v out = nominal output voltage v il t j = 25 c 1.2 1.0 t j = 40 to +125 c 0.8 on /off pin input current (test circuit figure 14) m a on /off pin = 5.0 v (aoffo), t j = 25 c i ih 15 30 on /off pin = 0 v (aono), t j = 25 c i il 0 5.0 notes: 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 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 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 aoffo. 7. v in = 40 v.
lm2575 5 motorola analog ic device data typical performance characteristics (circuit of figure 14) v out , output voltage change (%) 0 20 50 3.0 0 50 2.0 0 1.2 50 i q , quiescent current (ma) v in , input voltage (v) i o , output current (a) t j , junction temperature ( c) v in , input voltage (v) inputoutput differential (v) t j , junction temperature ( c) v sat , saturation voltage (v) switch current (a) 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 = 200 ma normalized at t j = 25 c figure 4. switch saturation voltage figure 5. current limit figure 6. dropout voltage figure 7. quiescent current i load = 200 ma t j = 25 c 3.3 v, 5.0 v and adj 12 v and 15 v 25 c v in = 25 v v out = 5.0 v measured at ground pin t j = 25 c i load = 200 ma i load = 1.0 a d v out = 5% r ind = 0.2 w 125 c 40 c 5.0 25 10 0 20 15 25 25 75 50 35 30 40 100 125 0.8 0.4 0.4 0 0 0.2 0.4 0.6 0.2 1.0 0.6 0.2 0.2 0.6 2.5 1.5 0.5 0 2.0 1.0 14 10 6.0 4.0 18 12 8.0 16 1.1 0.9 0.7 0.5 1.0 0.8 0.6 1.2 0.8 0.4 1.0 0.6 1.8 1.4 1.6 0.4 25 0.1 0 0.2 25 0.3 50 0.4 75 0.5 100 0.6 125 0.7 5.0 25 10 0 15 25 20 50 25 75 30 100 35 125 0.8 0.9 1.0 40 i load = 200 ma i load = 1.0 a
lm2575 6 motorola analog ic device data output voltage (pin 2) output current (pin 2) inductor output ripple voltage v out , output voltage i stby , standby quiescent current ( a) m 100 50 50 10 v 50 0 100 m s/div i fb , feedback pin current (na) t j , junction temperature ( c) t j , junction temperature ( c) 5.0 m s/div normalized frequency (%) t j , junction temperature ( c) i stby , standby quiescent current ( a) m figure 8. standby quiescent current v in , input voltage (v) figure 9. standby quiescent current figure 10. oscillator frequency figure 11. feedback pin current figure 12. switching waveforms figure 13. load transient response v in = 12 v v on /off = 5.0 v t j = 25 c 100 1.0 a 1.0 40 0 2.0 0.5 20 1.0 a 0 120 0 0 100 0.5 a 2.0 100 40 80 4.0 60 40 20 mv 8.0 20 0 10 0 0 0 40 80 120 60 20 6.0 /div i load , load current (a) 20 25 25 25 5.0 0 0 0 10 25 25 25 15 50 50 50 20 75 75 75 25 100 100 100 30 125 125 125 40 35 v in = 12 v normalized at 25 c adjustable version only change (mv) current
lm2575 7 motorola analog ic device data figure 14. typical test circuit d1 1n5819 l1 330 m h output 2 4 feedback c out 330 m f /16 v c in 100 m f/50 v lm25755 1 5 3on /off gnd v in load v out regulated output v in unregulated dc input 8.0 v 40 v d1 1n5819 l1 330 m h output 2 4 feedback c out 330 m f /16 v c in 100 m f/50 v lm2575 adjustable 1 5 3on /off gnd v in load v out regulated output unregulated dc input 8.0 v 40 v 5.0 output voltage versions adjustable output voltage versions v out v ref 1 r2 r1 r2 r1 v out v ref 1 where v ref = 1.23 v, r1 between 1.0 k w and 5.0 k w r2 r1 + + 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 14, 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 2 (emitter of the internal switch) of the lm2575 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 lm2575 regulator.
lm2575 8 motorola analog ic device data pin function description pin symbol description (refer to figure 1) 1 v in this pin is the positive input supply for the lm2575 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). 2 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. 3 gnd circuit ground pin. see the information about the printed circuit board layout. 4 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 lm2575 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. 5 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 1.4 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 1.4 v or if this pin is connected to ground, the regulator will be in the aono condition. design procedure buck converter basics the lm2575 is a abucko or stepdown converter which is the most elementary forwardmode converter. its basic schematic can be seen in figure 15. 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 15. basic buck converter d1 v in v out 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 catch dioded. 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 16 shows the buck converter idealized waveforms of the catch diode voltage and the inductor current. power switch figure 16. buck converter idealized waveforms 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
lm2575 9 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 dc input voltage i load(max) = maximum load current given parameters: v out = 5.0 v v in(max) = 20 v i load(max) = 0.8 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 lm25755 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 47 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 lm2575 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 30 v 1n5818 schottky diode, or any of the suggested fast recovery diodes shown in the table 4. 4. inductor selection (l1) a. according to the required working conditions, select the correct inductor value using the selection guide from figures 17 to 21 . 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 1 or table 2. when using table 2 for selecting the right inductor 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 f osc 4. inductor selection (l1) a. use the inductor selection guide shown in figures 17 to 21. b. from the selection guide, the inductance area intersected by the 20 v line and 0.8 a line is l330. c. inductor value required is 330 m h. from the table 1 or table 2 , choose an inductor from any of the listed manufacturers.
lm2575 10 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 lm2575 is a forwardmode switching regulator with voltage mode control, its open loop 2pole2zero 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 8v 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 = 16 v. procedure (adjustable output version: lm2575adj) 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 = 8.0 v v in(max) = 12 v i load(max) = 1.0 a 1. programming output voltage to select the right programming resistor r1 and r2 value (see figure 14) use the following formula: resistor r1 can be between 1.0 k and 5.0 k w . (for best temperature coefficient and stability with time, use 1% metal film resistors). v out v ref 1 r2 r1 r2 r1 v out v ref 1 where v ref = 1.23 v 1. programming output voltage (selecting r1 and r2) select r1 and r2: r2 = 9.91 k w , choose a 9.88 k metal film resistor. r2 r1 v out v ref 1 1.8 k 8.0 v 1.23 v 1 v out 1.23 1 r2 r1 select r1 = 1.8 k w 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 100 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 lm2575 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 3.0 a current rating is adequate. b. use a 20 v 1n5820 or mbr320 schottky diode or any suggested fast recovery diode in the table 4.
lm2575 11 motorola analog ic device data procedure (adjustable output version: lm2575adj) (continued) 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 21. 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 21. d. from the inductor code, identify the inductor value. then select an appropriate inductor from the table 1 or 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 ioad . 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. ext v in v out v out v on x 10 6 f[hz] [v x s] i p(max) i load(max) v in v out t on 2l t on v out v in x 1 f osc 4. inductor selection (l1) a. calculate e x t [v x m s] constant: b. e x t = 51 [v x m s] c. i load(max) = 1.0 a inductance region = l220 d. proper inductor value = 220 m h choose the inductor from the table 1 or table 2. ext ( 12 8.0 ) x 8.0 12 x 1000 52 51 [v x s] 5. output capacitor selection (c out ) a. since the lm2575 is a forwardmode switching regulator with voltage mode control, its open loop 2pole2zero 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 8v is appropriate, and a 10 v or 16 v rating is recommended. c out 7.785 v in(max) v out xl[ m h] [ m f] 5. output capacitor selection (c out ) a. to achieve an acceptable ripple voltage, select c out = 100 m f electrolytic capacitor. c out 7.785 12 8.220 53 m f
lm2575 12 motorola analog ic device data inductor value selection guide 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) 0.2 60 0.2 60 0.2 200 0.2 60 0.2 60 et, voltage time (v s) m i l , maximum load current (a) v in , maximum input voltage (v) figure 17. lm25753.3 i l , maximum load current (a) figure 18. lm25755.0 figure 19. lm257512 figure 20. lm257515 figure 21. lm2575adj note : this inductor value selection guide is applicable for continuous mode only. h1500 h1000 l680 l470 l330 l150 h1000 l100 l680 l470 l330 l220 l150 h1500 h1000 h1500 h1000 h680 h470 h680 h680 h2200 h2200 h2200 h1500 h1000 h470 h470 l330 l220 l150 l680 l680 l680 l470 l470 l470 l100 l220 l220 l330 l330 40 40 150 20 35 25 125 40 15 30 20 100 30 10 25 15 80 25 8.0 22 12 70 20 7.0 20 10 60 18 6.0 19 9.0 50 17 18 8.0 40 16 17 7.0 20 14 5.0 0.3 0.3 0.3 0.3 0.3 0.4 0.4 0.4 0.4 0.4 0.5 0.5 0.5 0.5 0.5 0.6 0.6 0.6 0.6 0.6 0.7 0.7 0.7 0.7 0.8 0.8 0.8 0.8 0.8 0.9 0.9 0.9 0.9 1.0 1.0 1.0 1.0 1.0 15 30 l220
lm2575 13 motorola analog ic device data table 1. inductor selection guide inductor code inductor value pulse eng renco aie tech 39 l100 100 m h pe92108 rl2444 4150930 77 308 bv l150 150 m h pe53113 rl1954 4150953 77 358 bv l220 220 m h pe52626 rl1953 4150922 77 408 bv l330 330 m h pe52627 rl1952 4150926 77 458 bv l470 470 m h pe53114 rl1951 4150927 l680 680 m h pe52629 rl1950 4150928 77 508 bv h150 150 m h pe53115 rl2445 4150936 77 368 bv h220 220 m h pe53116 rl2446 4300636 77 410 bv h330 330 m h pe53117 rl2447 4300635 77 460 bv h470 470 m h pe53118 rl1961 4300634 h680 680 m h pe53119 rl1960 4150935 77 510 bv h1000 1000 m h pe53120 rl1959 4150934 77 558 bv h1500 1500 m h pe53121 rl1958 4150933 h2200 2200 m h pe53122 rl2448 4150945 77 610 bv table 2. inductor selection guide inductance current schott renco pulse engineering coilcraft ( m h) (a) tht smt tht smt tht smt smt 68 0.32 67143940 67144310 rl12846843 rl150068 pe53804 pe53804s do160868 68 0.58 67143990 67144360 rl54706 rl150068 pe53812 pe53812s do3308683 68 0.99 67144070 67144450 rl54715 rl150068 pe53821 pe53821s do3316683 1.78 67144140 67144520 rl54715 pe53830 pe53830s do5022p683 100 0.48 67143980 67144350 rl54705 rl1500100 pe53811 pe53811s do3308104 100 0.82 67144060 67144440 rl54714 rl1500100 pe53820 pe53820s do3316104 1.47 67144130 67144510 rl54714 pe53829 pe53829s do5022p104 150 0.39 67144340 rl54704 rl1500150 pe53810 pe53810s do3308154 150 0.66 67144050 67144430 rl54713 rl1500150 pe53819 pe53819s do3316154 1.20 67144120 67144500 rl54713 pe53828 pe53828s do5022p154 220 0.32 67143960 67144330 rl54703 rl1500220 pe53809 pe53809s do3308224 220 0.55 67144040 67144420 rl54712 rl1500220 pe53818 pe53818s do3316224 1.00 67144110 67144490 rl54712 pe53827 pe53827s do5022p224 330 0.42 67144030 67144410 rl54711 rl1500330 pe53817 pe53817s do3316334 330 0.80 67144100 67144480 rl54711 pe53826 pe53826s do5022p334 note: table 1 and table 2 of this indicator selection guide shows some examples of different manufacturer products suitable for design with the lm2575.
lm2575 14 motorola analog ic device data table 3. example of several inductor manufacturers phone/fax numbers pulse engineering inc. phone fax + 16196748100 + 16196748262 pulse engineering inc. europe phone fax + 353 93 24 107 + 353 93 24 459 renco electronics inc. phone fax + 15166455828 + 15165865562 aie magnetics phone fax + 18133472181 coilcraft inc. phone fax + 17083222645 + 17086391469 coilcraft inc., europe phone fax + 44 1236 730 595 + 44 1236 730 627 tech 39 phone fax + 33 8425 2626 + 33 8425 2610 schott corp. phone fax + 16124751173 + 16124751786 table 4. diode selection guide gives an overview about both surfacemount and throughhole diodes for an effective design. device listed in bold are available from motorola. v schottky ultrafast recovery v 1.0 a 3.0 a 1.0 a 3.0 a v r smt tht smt tht smt tht smt tht 20 v sk12 1n5817 sr102 sk32 mbrd320 1n5820 mbr320 sr302 30 v mbrs130lt3 sk13 1n5818 sr103 11dq03 sk33 mbrd330 1n5821 mbr330 sr303 31dq03 murs120t3 mur120 11df1 her102 murs320t3 40 v mbrs140t3 sk14 10bq040 10mq040 1n5819 sr104 11dq04 mbrs340t3 mbrd340 30wq04 sk34 1n5822 mbr340 sr304 31dq04 10bf10 murd320 mur320 30wf10 mur420 50 v mbrs150 10bq050 mbr150 sr105 11dq05 mbrd350 sk35 30wq05 mbr350 sr305 11dq05 31df1 her302
lm2575 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 consequence of operating an electrolytic capacitor above 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 buck regulator d t on t v out v in and d t on t |v out | |v out | v in for a buck boost 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 0.05 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 lm2575 the lm2575 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 lm2575 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 a quality, low noise design requirements. table 4 provides a list of suitable diodes for the lm2575 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 has 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. continuous and discontinuous mode of operation the lm2575 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
lm2575 16 motorola analog ic device data conditions, the circuit will be forced to the discontinuous mode when inductor current falls to zero for certain period of time (see figure 22 and figure 23). 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 lm2575 regulator was added to this data sheet (figures 17 through 21). 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 200 ma) 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. figure 22. continuous mode switching current waveforms power switch 1.0 0 0 current (a) hortizontal time base: 5.0 m s/div 1.0 inductor current (a) 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. the inductor selection guide covers different styles of inductors, 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 completely 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 completely 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 lm2575 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 lm2575. different inductor types have different saturation characteristics, and this should be kept in mind when selecting an inductor. figure 23. discontinuous mode switching current waveforms 0.1 0.1 0 0 hortizontal time base: 5.0 m s/div power switch current (a) inductor current (a)
lm2575 17 motorola analog ic device data general recommendations output voltage ripple and transients source of the output ripple since the lm2575 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 24). 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 minimise 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. figure 24. output ripple voltage waveforms hortizontal time base: 10 m s/div unfilitered output voltage vertical resolution: 20 mv/div filitered output voltage voltage spikes caused by switching action of the output switch and the parasitic inductance of the output capacitor minimizing the output ripple in order to minimise 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 33) 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 24 shows the difference between filtered and unfiltered output waveforms of the regulator shown in figure 33. 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 throughhole package to220 the lm2575 is available in two packages, a 5pin to220(t, tv) and a 5pin surface mount d 2 pak(d2t). there are many applications that require no heatsink to keep the lm2575 junction temperature within the allowed operating range. the to220 package can be used without a heatsink for ambient temperatures up to approximately 50 c (depending on the output voltage and load current). higher ambient temperatures require some heatsinking, either to the printed circuit (pc) board or an external heatsink. the surface mount package d 2 pak and its heatsinking the other type of package, the surface mount d 2 pak, is designed to be soldered to the copper on the pc board. the copper and the board are the heatsink for this package and the other heat producing components, such as the catch diode and inductor. the pc board copper area that the package is soldered to should be at least 0.4 in 2 (or 100 mm 2 ) and ideally should have 2 or more square inches (1300 mm 2 ) of 0.0028 inch copper. additional increasing of copper area beyond approximately 3.0 in 2 (2000 mm 2 ) will not improve heat dissipation significantly. if further thermal improvements are needed, double sided or multilayer pc boards with large copper areas should be considered. thermal analysis and design the following procedure must be performed to determine whether or not a heatsink will be required. 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 lm2575). 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 in this data sheet or r q jc and r q ja values). the following formula is to calculate the total power dissipated by the lm2575: 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 lm2575 data sheet, v in is minimum input voltage applied, v o is the regulator output voltage, i load is the load current. the dynamic switching losses during turnon and turnoff can be neglected if proper type catch diode is used. packages not on a heatsink (freestanding) for a freestanding application when no heatsink 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.
lm2575 18 motorola analog ic device data packages on a heatsink if the actual operating junction temperature is greater than the selected safe operating junction temperature determined in step 3, than a heatsink is required. the junction temperature will be calculated as follows: t j = p d (r q ja + r q cs + r q sa ) + t a where r q jc is the thermal resistance junctioncase, r q cs is the thermal resistance caseheatsink, r q sa is the thermal resistance heatsinkambient. if the actual operating temperature is greater than the selected safe operating junction temperature, then a larger heatsink is required. 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. 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 colour of the traces. the size, quantity and spacing of other components on the board can also influence its effectiveness to dissipate the heat. figure 25. inverting buckboost regulator using the lm257512 develops 12 v @ 0.35 a d1 1n5819 l1 100 m h output 2 4 feedback unregulated dc input 12 v to 25 v c in 100 m f /50 v 1 5 3on /off gnd +v in regulated output 12 v @ 0.35 a c out 1800 m f /16 v lm257512 additional applications inverting regulator an inverting buckboost regulator using the lm257512 is shown in figure 25. 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 lm257512 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 0.35 a to the output when the input voltage is 12 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 1.5 a. such an amount of input startup current is needed for at least 2.0 ms or more. the actual time depends on the output voltage and size of the output capacitor. 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. 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 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. the following formula is used to obtain the peak inductor current: where t on |v o | v in |v o | x 1 f osc , and f osc 52 khz. i peak i load (v in |v o |) v in v in xt on 2l 1 under normal continuous inductor current operating conditions, the worst case occurs when v in is minimal. note that the voltage appearing across the regulator is the absolute sum of the input and output voltage, and must not exceed 40 v.
lm2575 19 motorola analog ic device data figure 26. inverting buckboost regulator with delayed startup d1 1n5819 l1 100 m h output 2 4 feedback unregulated dc input 12 v to 25 v c in 100 m f /50 v 1 3 5on /off gnd +v in regulated output 12 v @ 0.35 a c out 1800 m f /16 v lm257512 c1 0.1 m f r1 47 k r2 47 k 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 applied to a buckboost converter is shown in figure 26 . figure 32 in the aundervoltage lockouto section describes an undervoltage lockout feature for the same converter topology. figure 27. inverting buckboost regulator shut down circuit using an optocoupler lm2575xx 1 3 5 gnd on /off +v in r2 47 k c in 100 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 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 (1.4 v approximately) has to be related to the negative output voltage level. there are many different possible shut down methods, two of them are shown in figures 27 and 28. figure 28. inverting buckboost regulator shut down circuit using a pnp transistor note : this picture does not show the complete circuit. r2 5.6 k q1 2n3906 lm2575xx 1 3 5 gnd on /off r1 12 k v out +v in shutdown input off on +v 0 +v in c in 100 m f negative boost regulator this example is a variation of the buckboost topology and is called a 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 29 shows the negative boost configuration. the input voltage in this application ranges from 5.0 v 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. figure 29. negative boost regulator 1n5817 150 m h output 2 4 feedback regulated output v out = 12 v load current from 200 ma for v in = 5.2 v to 500 ma for v in = 7.0 v unregulated dc input v in = 5.0 v to 12 v l1 d1 c out 1000 m f /16 v c in 100 m f /50 v lm257512 1 5 3 on /off gnd +v in
lm2575 20 motorola analog ic device data 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 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 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 the input voltage is applied and the time when the output voltage comes up, the circuit in figure 30 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 1.4 v, the regulator starts up. resistor r1 is included to limit the maximum voltage applied to the on /off pin, 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. figure 30. delayed startup circuitry r1 47 k lm2575xx 1 3 5 gnd on /off r2 47 k +v in +v in c1 0.1 m f c in 100 m f note : this picture does not show the complete circuit. undervoltage lockout some applications require the regulator to remain off until the input voltage reaches a certain threshold level. figure 31 shows an undervoltage lockout circuit applied to a buck regulator. a version of this circuit for buckboost converter is shown in figure 32. 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 r2 r1 v be ( q1 ) figure 31. undervoltage lockout circuit for buck converter r2 10 k z1 1n5242b r1 10 k q1 2n3904 r3 47 k v th 13 v c in 100 m f lm25755.0 1 3 5 gnd on /off +v in +v in note : this picture does not show the complete circuit. figure 32. undervoltage lockout circuit for buckboost converter r2 15 k z1 1n5242b r1 15 k q1 2n3904 r3 68 k v th 13 v c in 100 m f lm25755.0 1 3 5 gnd on /off +v in +v in v out = 5.0 v note : this picture does not show the complete circuit. adjustable output, lowripple power supply a 1.0 a output current capability power supply that features an adjustable output voltage is shown in figure 33. this regulator delivers 1.0 a into 1.2 v to 35 v output. the input voltage ranges from roughly 8.0 v 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.
lm2575 21 motorola analog ic device data figure 33. adjustable power supply with low ripple voltage d1 1n5819 l1 150 m h output 2 4 feedback r2 50 k r1 1.1 k l2 20 m h regulated output voltage 1.2 v to 35 v @1.0 a optional output ripple filter unregulated dc input + c out 2200 m f c1 100 m f c in 100 m f /50 v lm2575adj 1 5 3on /off gnd +v in r , thermal resistance ja q junction-to-air ( c/w) 30 40 50 60 70 80 1.0 1.5 2.0 2.5 3.0 3.5 0102030 25 15 5.0 l, length of copper (mm) minimum size pad 2.0 oz. copper l l ???? ???? ???? free air mounted vertically p d , maximum power dissipation (w) figure 34. d 2 pak thermal resistance and maximum power dissipation versus p.c.b. copper length p d(max) for t a = 50 c r q ja
lm2575 22 motorola analog ic device data the lm25755.0 stepdown voltage regulator with 5.0 v @ 1.0 a output power capability. typical application with throughhole pc board layout dcdc converter figure 35. schematic diagram of the lm25755.0 stepdown converter figure 36. printed circuit board component side figure 37. printed circuit board copper side d1 1n5819 l1 330 m h output 2 4 feedback unregulated dc input +v in = +7.0 v to +40 v c out 330 m f /16 v c1 100 m f /50 v lm25755.0 1 5 3on /off gnd +v in j1 regulated output +v out1 = 5.0 v @ 1.0 a gnd in gnd out c1 100 m f, 50 v, aluminium electrolytic c2 330 m f, 16 v, aluminium electrolytic d1 1.0 a, 40 v, schottky rectifier, 1n5819 l1 330 m h, tech 39: 77 458 bv, toroid core, throughhole, pin 3 = start, pin 7 = finish note: not to scale. note: not to scale . +v out1 +v in gnd in gnd out c1 l1 c2 d1 j1 u1 lm2575
lm2575 23 motorola analog ic device data the lm2575adj stepdown voltage regulator with 8.0 v @ 1.0 a output power capability. typical application with throughhole pc board layout c1 100 m f, 50 v, aluminium electrolytic c2 330 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, tech 39: 77 458 bv, toroid core, throughhole, pin 3 = start, pin 7 = finish l2 25 m h, tdk: sft52501, toroid core, throughhole r1 1.8 k r2 10 k figure 38. schematic diagram of the 8.0 v @ 1.0 v stepdown converter using the lm2575adj (an additional lc filter is included to achieve low output ripple voltage) figure 39. pc board component side figure 40. pc board copper side v ref = 1.23 v r1 is between 1.0 k and 5.0 k d1 1n5819 l1 330 m h output 2 r2 10 k r1 1.8 k l2 25 m h regulated output filtered v out2 = 8.0 v @1.0 a unregulated dc input c2 330 m f /16 v c3 100 m f /16 v c1 100 m f /50 v lm2575adj 1 5 3on /off gnd +v in +v in = +10 v to + 40 v 4 feedback regulated output unfiltered v out1 = 8.0 v @1.0 a v out v ref 1 r2 r1 +v out1 +v in gnd in c1 l1 c2 d1 j1 u1 lm2575 l2 c3 +v out2 r2 r1 gnd out motorola note: not to scale. note: not to scale . references ? national semiconductor lm2575 data sheet and application note ? national semiconductor lm2595 data sheet and application note ? marty brown apratical switching power supply designo, academic press, inc., san diego 1990 ? ray ridley ahigh frequency magnetics designo, ridley engineering, inc. 1995
lm2575 24 motorola analog ic device data t suffix plastic package case 314d03 issue d tv suffix plastic package case 314b05 issue j outline dimensions q 12345 u k d g s a b 5 pl j h l e c m q m 0.356 (0.014) t seating plane t dim min max min max millimeters inches a 0.572 0.613 14.529 15.570 b 0.390 0.415 9.906 10.541 c 0.170 0.180 4.318 4.572 d 0.025 0.038 0.635 0.965 e 0.048 0.055 1.219 1.397 g 0.067 bsc 1.702 bsc h 0.087 0.112 2.210 2.845 j 0.015 0.025 0.381 0.635 k 1.020 1.065 25.908 27.051 l 0.320 0.365 8.128 9.271 q 0.140 0.153 3.556 3.886 u 0.105 0.117 2.667 2.972 s 0.543 0.582 13.792 14.783 notes: 1. dimensioning and tolerancing per ansi y14.5m, 1982. 2. controlling dimension: inch. 3. dimension d does not include interconnect bar (dambar) protrusion. dimension d including protrusion shall not exceed 10.92 (0.043) maximum. v q k f u a b g p m 0.10 (0.254) p m t 5x j m 0.24 (0.610) t optional chamfer s l w e c h n t seating plane notes: 1. dimensioning and tolerancing per ansi y14.5m, 1982. 2. controlling dimension: inch. 3. dimension d does not include interconnect bar (dambar) protrusion. dimension d including protrusion shall not exceed 0.043 (1.092) maximum. dim min max min max millimeters inches a 0.572 0.613 14.529 15.570 b 0.390 0.415 9.906 10.541 c 0.170 0.180 4.318 4.572 d 0.025 0.038 0.635 0.965 e 0.048 0.055 1.219 1.397 f 0.850 0.935 21.590 23.749 g 0.067 bsc 1.702 bsc h 0.166 bsc 4.216 bsc j 0.015 0.025 0.381 0.635 k 0.900 1.100 22.860 27.940 l 0.320 0.365 8.128 9.271 n 0.320 bsc 8.128 bsc q 0.140 0.153 3.556 3.886 s 0.620 15.748 u 0.468 0.505 11.888 12.827 v 0.735 18.669 w 0.090 0.110 2.286 2.794 5x d
lm2575 25 motorola analog ic device data d2t suffix plastic package case 936a02 (d 2 pak) issue a outline dimensions 5 ref a 123 k b s h d g c e m l p n r v u terminal 6 notes: 1 dimensioning and tolerancing per ansi y14.5m, 1982. 2 controlling dimension: inch. 3 tab contour optional within dimensions a and k. 4 dimensions u and v establish a minimum mounting surface for terminal 6. 5 dimensions a and b do not include mold flash or gate protrusions. mold flash and gate protrusions not to exceed 0.025 (0.635) maximum. dim a min max min max millimeters 0.386 0.403 9.804 10.236 inches b 0.356 0.368 9.042 9.347 c 0.170 0.180 4.318 4.572 d 0.026 0.036 0.660 0.914 e 0.045 0.055 1.143 1.397 g 0.067 bsc 1.702 bsc h 0.539 0.579 13.691 14.707 k 0.050 ref 1.270 ref l 0.000 0.010 0.000 0.254 m 0.088 0.102 2.235 2.591 n 0.018 0.026 0.457 0.660 p 0.058 0.078 1.473 1.981 r 5 ref s 0.116 ref 2.946 ref u 0.200 min 5.080 min v 0.250 min 6.350 min 45 m 0.010 (0.254) t t optional chamfer
lm2575 26 motorola analog ic device data notes
lm2575 27 motorola analog ic device data notes
lm2575 28 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, 4321, p.o. box 5405, denver, colorado 80217. 3036752140 or 18004412447 nishigotanda, shinagawaku, tokyo 141, japan. 81354878488 mfax ? : rmfax0@email.sps.mot.com touchtone 6 022446609 asia / pacific : motorola semiconductors h.k. ltd.; 8b tai ping industrial park, us & canada only 18007741848 51 ting kok road, tai po, n.t., hong kong. 85226629298 internet : http://motorola.com/sps ? lm2575/d

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