august 1999 1 LM2574 LM2574 micrel ordering information part number temp. range package LM2574bn C40 c to +85 c 8-pin plastic dip LM2574bwm C40 c to +85 c 14-pin wide soic LM2574-3.3bn C40 c to +85 c 8-pin plastic dip LM2574-3.3bwm C40 c to +85 c 14-pin wide soic LM2574-5.0bn C40 c to +85 c 8-pin plastic dip LM2574-5.0bwm C40 c to +85 c 14-pin wide soic LM2574-12bn C40 c to +85 c 8-pin plastic dip LM2574-12bwm C40 c to +85 c 14-pin wide soic LM2574 52khz simple 0.5a buck regulator features ? 3.3v, 5v, 12v, and adjustable output versions ? adjustable version output 1.23v to 37v 4% max. over line and load conditions. ? guaranteed 0.5a output current ? wide input voltage, up to 40v ? thermal shutdown and current limit protection ? requires only 4 external components. ? shutdown capability (standby mode) ? low power standby mode < 200 m a typical ? high efficiency ? 52khz fixed frequency internal oscillator ? uses standard inductors applications ? simple high-efficiency step-down (buck) regulator ? efficient pre-regulator for linear regulators ? on-card switching regulators ? positive to negative converter (buck-boost) general description the LM2574 family is a series of easy to use fixed and adjustable switching voltage regulators. the LM2574 con- tains all of the active circuitry necessary to construct a stepdown (buck) switching regulator and requires a minimum of external components. the LM2574 is available in 3.3v, 5v, and 12v fixed output versions, or an adjustable version with an output voltage range of 1.23v to 37v. output voltage is guaranteed to 4% for specified input and load conditions. the LM2574 can supply 0.5a while maintaining excellent line and load regulation. the output switch includes cycle-by- cycle current limiting, as well as thermal shutdown for full protection under fault conditions. an external shutdown connection selects operating or standby modes. standby current is less than 200 m a. heat sinks are generally unnecessary due the regulators high efficiency. adequate heat transfer is usually provided by soldering all package pins to a printed circuit board. the LM2574 includes internal frequency compensation and an internal 52khz fixed frequency oscillator guaranteed to 10% of the frequency. circuits constructed around the LM2574 use a standard series of inductors which are available from several different manufacturers. pin configuration 8-pin dip (n) fb 1 sig gnd 2 on/off 3 pwr gnd 4 8* 7 output 6* 5v in 14-pin soic (wm) *1 *2 fb 3 sig gnd 4 on/off 5 pwr gnd 6 *7 14 * 13 * 12 output 11 * 10 v in 9* 8* * nc: solder to printed circuit for maximum heat transfer figure 1. fixed output regulator circuit v in pwr gnd sig gnd on/ off out fb LM2574 c in 22? 40v max unregulated dc in regulated output 0.5a 11dq05 c out 220? 330? typical application
LM2574 micrel LM2574 2 august 1999 absolute maximum ratings maximum supply voltage LM2574 ..................................................................... 45v off pin input voltage ................................ C0.3v v v in output voltage to ground (steady state) ..................... C1v power dissipation .................................... internally limited storage temperature range ................... C65 c to +150 c minimum esd rating c = 100pf, r = 1.5k w ............................................... 2kv fb pin ....................................................................... 1kv lead temperature (soldering, 10 sec.) ..................... 260 c maximum junction temperature ............................... 150 c electrical characteristics specifications with standard typeface are for t j = 25 c, and those with boldface type apply over full operating temperature range. unless otherwise specified, v in = 12v, and i load = 100ma. symbol parameter condition min typ max units system parameters, adjustable regulators (note 3) test circuit figure 2 v out feedback voltage v in = 12v, i load = 0.1a, v out = 5v 1.217 1.230 1.243 v v out feedback voltage 0.1a i load 0.5a, 7v v in 40v, v out = 5v 1.193 1.230 1.267 v (LM2574) 1.180 1.280 v h efficiency v in = 12v, i load = 0.1a, v out = 5v 78 % system parameters, 3.3v regulators (note 3) test circuit figure 3 v out output voltage v in = 12v, i load = 0.1a, v out = 3.3v 3.234 3.3 3.366 v v out output voltage 0.1a i load 0.5a, 4.75v v in 40v, 3.168 3.3 3.432 v (LM2574-3.3) v out = 3.3v 3.135 3.465 v h efficiency v in = 12v, i load = 0.1a 73 % system parameters, 5v regulators (note 3) test circuit figure 3 v out output voltage v in = 12v, i load = 0.1a, v out = 5v 4.900 5.0 5.100 v v out output voltage 0.1a i load 0.5a, 7v v in 40v, 4.800 5.0 5.200 v (LM2574-5.0) v out = 5v 4.750 5.250 v h efficiency v in = 12v, i load = 0.1a, v out = 5v 78 % system parameters, 12v regulators (note 3) test circuit figure 3 v out output voltage v in = 25v, i load = 0.1a, v out = 12v 11.760 12 12.240 v v out output voltage 0.1a i load 0.5a, 15v v in 40v, 11.520 12 12.480 v (LM2574-12) v out = 12v 11.400 12.600 v h efficiency v in = 25v, i load = 0.1a 88 % operating ratings temperature range LM2574 ........................................... 40 c t j +125 c supply voltage LM2574 ..................................................................... 40v
august 1999 3 LM2574 LM2574 micrel electrical characteristics (continued) symbol parameter condition min typ max units device parameters, adjustable regulator i b feedback bias current v out = 5v 50 100 na 500 na device parameters, fixed and adjustable regulators f o oscillator frequency note 8 47 52 58 khz 42 63 khz v sat saturation voltage i out = 0.5a, note 4 0.8 1.2 v 1.4 v dc max duty cycle (on) note 5 93 98 % i cl current limit peak current, t on 3 m s, note 4 0.7 1.0 1.6 a 0.65 1.8 i l output leakage current v in , note 6 , output = 0v 2 ma note 6 , output = C1v 7.5 30 i q quiescent current note 6 510ma i stby standby quiescent current on/off pin = 5v (off) 50 200 m a q ja thermal resistance n package, junction to ambient, note 7 85 c/w wm package, junction to ambient, note 7 100 c/w on/off control, fixed and adjustable regulators test circuit figures 2, 3 v ih on/off input level v out = 0v 2.2 1.4 v 2.4 v v il on/off input level v out = 5v 1.2 1.0 v 0.8 v i ih on/off logic current on/off = 5v (off) 4 30 m a i il on/off logic current on/off = 0v (on) 0.01 10 m a note 1 absolute maximum ratings indicate limits beyond which damage to the device may occur. operating ratings indicate 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. note 2 all limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face) . all room temperature limits are 100% production tested. all limits at temperature extremes are guaranteed via testing. note 3 external components such as the catch diode, inductor, input and output capacitors can affect switching regulator system perfor mance. when the LM2574 is used as shown in figure 1 test circuit, system performance will be shown in system parameters section of electrical character- istics. note 4 output (pin 2) sourcing current. no diode, inductor, or capacitor connected to input. note 5 feedback (pin 4) removed from output and connected to 0v. note 6 feedback (pin 4) removed from output and connected to 12v to force the output transistor off. note 7 junction to ambient thermal resistance with approximately 1 square inches of pc board copper surrounding the leads.
LM2574 micrel LM2574 4 august 1999 typical performance characteristics (circuit of figure 1) supply current input voltage (v) supply current (ma) 20 measured at ground pin t j = 25?c v out = 5v 18 16 14 12 10 8 6 4 0 102030405060 i load to 0.5a supply current vs. duty cycle duty cycle (%) 20.0 17.5 15.0 12.5 10.0 7.5 5.0 2.5 0 0 2040 6080100 v in from 7v to 40v i load = 100 ma supply current (ma) junction temperature (?c) 200 150 100 50 0 -75 v in = 12v standby quiescent current (?) standby quiescent current v in = 40v -50 -25 0 25 50 75 100 125 150 current limit junction temperature (?c) 1.5 1 0.5 0 -75 vi n = 25v output current (a) input voltage (v) 100 efficiency (%) efficiency v out = 12v -50 -25 0 25 50 75 100 125 150 95 90 85 80 75 70 65 60 100 ma 100 ma v out = 3v 0.5a 0.5a 0 5 10 15 20 25 30 35 40 minimum operating voltage junction temperature (?c) 5.0 i load = 100 ma input voltage (v) line regulation input voltage (v) 14 0 normalized feedback voltage (mv) junction temperature (?c) 100 -100 -75 standby quiescent current (na) feedback pin current -50 -25 0 25 50 75 100 125 150 v out = 1.23v 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 -75 -50 -25 0 25 50 75 100 125 150 12 10 8 6 4 2 0 -2 -4 -6 5 1015202530 75 50 25 0 -25 -50 -75 junction temperature (?c) +8 -8 -75 normalized frequency (%) oscillator frequency -50 -25 0 25 50 75 100 125 150 +6 +4 +2 0 -2 -4 --6 v in = 12v v in = 40v normalized at 25?c normalized to v in = 10v v out = 5v i load = 100ma t j = 25 v on/off = 5v switch saturation voltage switch current (a) 1.1 -55?c 0.9 0.7 0.5 0.3 0 saturation voltage (v) 0.1 0.2 0.3 0.4 0.5 25?c 125?c 150?c -40?c dropout voltage junction temperature (?c) input-output differential (v) 2.0 -75 -50 -25 0 25 50 75 100 125 150 d v out = 5% r ind = 0.2 w i load = 0.5a i load = 100 ma 1.5 1.0 0.5 0 normalized output voltage junction temperature (?c) output voltage change (mv) 100 75 50 25 0 -25 -50 -75 -100 -75 -50 -25 0 25 50 75 100 125 150 v in = 12v i load = 100ma normalized to t j = 25?c v out = 5v
august 1999 5 LM2574 LM2574 micrel typical performance characteristics (continued) normalized feedback voltage* junction temperature (?c) normalized feedback voltage (mv) 25 20 15 10 5 0 -5 -10 -15 -20 -25 -75 -50 -25 0 25 50 75 100 125 150 v in = 12v i load = 100ma normalized to t j = 25?c feedback voltage vs duty cycle* duty cycle (%) feedback voltage change (mv) 20 15 10 5 0 -5 -10 -15 -20 i load = 100 ma v in = 40v v in = 7v 0 20 40 60 80 100 * adjustable version only on/off comparator fixed gain error amp 1/2 amp switch output driver + - + - v in feed- back 1.23v band-gap reference 52 khz oscillator reset thermal shutdown current limit 5 2 3 1 note: pin numbers are for the to-220 package internal regulator on/off gnd on/off comparator fixed gain error amp 1/2 amp switch output driver + - + - v in feed- back 1.23v band-gap reference 52 khz oscillator reset thermal shutdown current limit 5 2 3 1 4 internal regulator on/off gnd 3.1k 1.0k 4 block diagrams fixed regulator adjustable regulator v in pwr gnd sig gnd on/ off out fb LM2574 (adjustable) c in 22? 11dq06 c out 220? 330? 3.09k 1k load v in pwr gnd sig gnd on/ off out fb LM2574 3.3, 5, 12 c in 22? 11dq06 c out 220? 330? load figure 3. fixed regulator test circuit figure 2. adjustable regulator test circuit
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