MIC4574 micrel 4-92 april 1998? MIC4574 200khz simple 0.5a buck voltage regulator general description the MIC4574 is a series of easy to use fixed and adjustable bicmos step-down (buck) switch-mode voltage regulators. the 200khz MIC4574 duplicates the pinout and function of the 52khz lm2574. the higher switching frequency may allow up to a 2:1 reduction in output filter inductor size. the MIC4574 is available in 3.3v, and 5v fixed output versions or a 1.23v to 20v adjustable output version. both versions are capable of driving a 0.5a load with excellent line and load regulation. the feedback voltage is guaranteed to 2% tolerance for adjustable versions, and the output voltage is guaranteed to 3% for fixed versions, within specified voltages and load conditions. the oscillator frequency is guaranteed to 10%. in shutdown mode, the regulator draws less than 200 m a standby current. the regulator performs cycle-by-cycle current limiting and thermal shutdown for protection under fault conditions. this series of simple switch-mode regulators requires a minimum number of external components and can operate using a standard series of inductors. frequency compensa- tion is provided internally. the MIC4574 is available in dip (n) and soic (wm) pack- ages for the industrial temperature range. typical applications c1 47? 35v d1 1n5819 c2 220? 16v l1 100? sgnd fb sw MIC4574-5.0bn shdn 8v to 24v 5.0v/0.5a v in pgnd 24 1 7 3 5 shutdown enable fixed regulator c1 10? 35v d1 c2 330? 6.3v l1 100? sgnd fb sw MIC4574bwm shdn 6v to 24v 3.3v/0.5a v in r2 2.49k 1% r1 1.50k 1% pgnd 3 12 6 4 10 5 c3 3300pf mbrs130lt3 shutdown enable adjustable regulator features ? fixed 200khz operation ? 3.3v, 5v, and adjustable output versions ? voltage over specified line and load conditions: fixed version: 3% max. output voltage adjustable version: 2% max. feedback voltage ? guaranteed 0.5a switch current ? wide 4v to 24v input voltage range ? wide 1.23v to 20v output voltage range ? requires minimum external components ? < 200 m a typical shutdown mode ? 75% efficiency (adjustable version > 75% typ.) ? standard inductors and capacitors are 25% of typical lm2574 values ? thermal shutdown ? overcurrent protection ? 100% electrical thermal limit burn-in applications ? simple high-efficiency step-down (buck) regulator ? efficient preregulator for linear regulators ? on-card switching regulators ? positive-to-negative converter (inverting buck-boost) ? isolated flyback converter using minimum external components ? negative boost converter
april 1998? 4-93 MIC4574 micrel 4 ordering information part number voltage temperature range package MIC4574-3.3bn 3.3v C40 c to +85 c 8-pin dip MIC4574-5.0bn 5.0v C40 c to +85 c 8-pin dip MIC4574bn adjustable C40 c to +85 c 8-pin dip MIC4574-3.3bwm 3.3v C40 c to +85 c 14-lead soic MIC4574-5.0bwm 5.0v C40 c to +85 c 14-lead soic MIC4574bwm adjustable C40 c to +85 c 14-lead soic pin configuration 1 2 3 4 8 7 6 5 fb sgnd shdn pgnd nc sw nc v in 8-pin dip (n) 14-lead wide soic (wm) 2 nc nc 13 3 fb sw 12 4 sgnd nc 11 5 shdn v in 10 6 pgnd nc 9 7 nc nc 8 1 nc nc 14 pin description pin number pin number pin name pin function n package wm package 1 nc not internally connected. solder to printed circuit for maximum heat transfer. 2 nc not internally connected. solder to printed circuit for maximum heat transfer. 1 3 fb feedback (input): output voltage feedback to regulator. connect to output of supply for fixed versions. connect to 1.23v tap of resistive divider for adjustable versions. 2 4 sgnd signal ground 3 5 shdn shutdown (input): logic low enables regulator. logic high (> 2.4v) shuts down regulator. 4 6 pgnd power ground 7 nc not internally connected. solder to printed circuit for maximum heat transfer. 8 nc not internally connected. solder to printed circuit for maximum heat transfer. 9 nc not internally connected. solder to printed circuit for maximum heat transfer. 510 v in supply voltage (input): unregulated +4v to +24v supply voltage. 11 nc not internally connected. solder to printed circuit for maximum heat transfer. 7 12 sw switch (output): emitter of npn output switch. connect to external storage inductor and shottky diode. 8 13 nc not internally connected. solder to printed circuit for maximum heat transfer. 14 nc not internally connected. solder to printed circuit for maximum heat transfer.
MIC4574 micrel 4-94 april 1998? electrical characteristics v in =12v; i load = 100ma; t a = 25 c, bold values indicate C40 c t a +85 c; unless noted parameter condition min typ max units MIC4574 [adjustable] feedback voltage 1.217 1.230 1.243 v feedback voltage 8v v in 24v, 0.1a i load 0.5a 1.193 1.230 1.267 v 1.180 1.280 v efficiency i load = 0.5a, v out = 5v 77 % feedback bias current 50 100 na 500 na MIC4574-3.3 output voltage 3.234 3.3 3.366 v output voltage 6v v in 24v, 0.1a i load 0.5a 3.168 3.3 3.432 v 3.135 3.465 v efficiency 72 % MIC4574-5.0 output voltage 4.900 5.0 5.100 v output voltage 8v v in 24v, 0.1a i load 0.5a 4.800 5.0 5.200 v 4.750 5.250 v efficiency 77 % MIC4574 / -3.3 / -5.0 oscillator frequency 180 200 220 khz saturation voltage i out = 0.5a 1 1.3 v 1.5 v maximum duty cycle (on) fb connected to 0v 90 95 % current limit peak current, t on 3 m s 0.7 1.0 1.6 a 0.65 1.8 a output leakage current v in = 24v, fb connected to 6v output = 0v 0 2 ma output = C1v 7.5 30 ma quiescent current 510ma standby quiescent current shdn = 5v (regulator off) 50 200 m a shdn input logic level v out = 0v (regulator off) 2.2 1.4 v 2.4 v v out = 3.3v or 5v (regulator on) 1.2 1.0 v 0.8 v shdn input current shdn = 5v (regulator off) 4 30 m a shdn = 0v (regulator on) C10 0.01 10 m a general note: devices are esd protected, however, handling precautions are recommended. note 1: the MIC4574 is not guaranteed to survive a short circuit to ground for input voltage above 24v. absolute maximum ratings supply voltage (v in ) note 1 ....................................... +40v shutdown (v shdn ) ....................................... C0.3v to +36v output switch (v sw ) steady state ................................. C1v junction temperature (t j ) ...................................... +150 c storage temperature ............................... C65 c to +150 c operating ratings supply voltage (v in ) ................................................... +24v package thermal resistance q ja plastic dip .................................................. 130 c/w q jc soic ........................................................... 120 c/w
april 1998? 4-95 MIC4574 micrel 4 200khz oscillator 1.23v bandgap 0.5a switch thermal shutdown current limit driver internal regulator fb sw gnd v in +24v max. c in c out l1 d1 shutdown enable shdn v out MIC4574 [adjustable] r1 r2 com- parator error amp. v out
MIC4574 micrel 4-96 april 1998? functional description the MIC4574 is a variable duty cycle switch-mode regulator with an internal power switch. refer to the block diagrams. supply voltage the MIC4574 operates from a +4v to +24v unregulated input. highest efficiency operation is from a supply voltage below +15v. enable/shutdown the shutdown ( shdn ) input is ttl compatible. ground the input if unused. a logic-low enables the regulator. a logic- high shuts down the internal regulator which reduces the current to typically 50 m a. feedback fixed versions of the regulator have an internal resistive divider from the feedback ( fb ) pin. connect fb directly to the output line. adjustable versions require an external resistive voltage divider from the output voltage to ground, connected from the 1.23v tap to fb . duty cycle control a fixed-gain error amplifier compares the feedback signal with a 1.23v bandgap voltage reference. the resulting error amplifier output voltage is compared to a 200khz sawtooth waveform to produce a voltage controlled variable duty cycle output. a higher feedback voltage increases the error amplifier output voltage. a higher error amplifier voltage (comparator inverting input) causes the comparator to detect only the peaks of the sawtooth, reducing the duty cycle of the com- parator output. a lower feedback voltage increases the duty cycle. output switching when the internal switch is on, an increasing current flows from the supply v in, through external storage inductor l1, to output capacitor c out and the load. energy is stored in the inductor as the current increases with time. when the internal switch is turned off, the collapse of the magnetic field in l1 forces current to flow through fast recovery diode d1, charging c out . output capacitor external output capacitor c out provides stabilization and reduces ripple. return paths during the on portion of the cycle, the output capacitor and load currents return to the supply ground. during the off portion of the cycle, current is being supplied to the output capacitor and load by storage inductor l1, which means that d1 is part of the high-current return path. applications information the applications circuits that follow have been constructed and tested. refer to application note 15 for additional information, including efficiency graphs and manufacturers addresses and telephone numbers for most circuits. for a mathematical approach to component selection and circuit design, refer to application note 14. c1 47? 35v d1 1n5819 c2 220? 16v l1 100? sgnd fb sw MIC4574-3.3bn shdn 6v to 24v 3.3v/0.5a v in c1 nichicon upl1v470meh, esr = 0.34 w c2 nichicon upl1c221mph, esr = 0.16 w d1 motorola 1n5819 l1 sumida rch875-101k, dcr = 0.28 w pgnd 24 1 7 3 5 figure 1. 6vC24v to 3.3v/0.5a buck converter through hole c1 47? 35v d1 1n5819 c2 220? 16v l1 100? sgnd fb sw MIC4574-5.0bn shdn 8v to 24v 5.0v/0.5a v in c1 nichicon upl1j470meh, esr = 0.34 w c2 nichicon upl1c221mph, esr = 0.16 w d1 motorola 1n5819 l1 sumida rch875-101k, dcr = 0.28 w pgnd 24 1 7 3 5 figure 2. 8vC24v to 5v/0.5a buck converter through hole c1 33? 63v mbr160 c2 220? 16v l1 220? sgnd fb sw MIC4574bn shdn 16v to 24v 12v/0.5a v in r2 13.0k 1% r1 1.50k 1% c1 nichicon upl1j330meh, esr = 0.35 w c2 nichicon upl1c221mph, esr = 0.16 w d1 motorola mbr160 l1 sumida rch106-221k, dcr = 0.78 w pgnd 1 7 4 2 5 3 figure 3. 16vC24v to 12v/0.5a buck converter through hole
april 1998? 4-97 MIC4574 micrel 4 c1 68? 35v d1 mbrs130lt3 c2 470? 16v l1 100? sgnd fb sw MIC4574-3.3bwm shdn 6v to 24v 3.3v/0.5a v in c1 sanyo 35cv168gx, esr = 0.34 w c2 sanyo 16cv470gx, esr = 0.17 w d1 motorola mbrs130lt3 l1 coilcraft do3316p-104, dcr = 0.23 w pgnd 46 3 12 5 10 figure 7. 6v?4v to 3.3v/0.5a buck converter low-cost surface mount c1 68? 35v d1 mbrs130lt3 c2 470? 16v l1 100? sgnd fb sw MIC4574-5.0bwm shdn 8v to 24v 5v/0.5a v in c1 sanyo 35cv168gx, esr = 0.34 w c2 sanyo 16cv470gx, esr = 0.17 w d1 motorola mbrs130lt3 l1 coilcraft do3316p-104, dcr = 0.23 w pgnd 46 3 12 5 10 figure 8. 8v?4v to 5v/0.5a buck converter low-cost surface mount c1 47? 50v d1 ss16 c2 470? 16v l1 220? sgnd fb sw MIC4574bwm shdn 16v to 24v 12v/0.5a v in r2 13.0k 1% r1 1.50k 1% c1 nichicon uux1h470mnt1gs, esr = 0.4 w c2 sanyo 16cv470gx, esr = 0.17 w d1 general instruments ss16 l1 coilcraft do3316-224, dcr = 0.53 w pgnd 3 12 6 4 10 5 figure 9. 16vC24v to 12v/0.5a buck converter low-cost surface mount c1 10? 35v d1 c2 330? 6.3v l1 100? sgnd fb sw MIC4574bwm shdn 6v to 24v 3.3v/0.5a v in r2 2.49k 1% r1 1.50k 1% c1 avx tpsd106m035r0300, esr = 0.3 w c2 avx tpse337m006r0100, esr = 0.1 w d1 motorola mbrs130lt3 l1 coiltronics ctx100-2p, dcr = 0.541 w pgnd 3 12 6 4 10 5 c3 3300pf mbrs130lt3 figure 4. 6vC24v to 3.3v/0.5a buck converter low-profile surface mount c1 10? 35v d1 c2 220? 10v l1 100? sgnd fb sw MIC4574bwm shdn 8v to 24v 5v/0.5a v in r2 3.01k 1% r1 1.00k 1% c1 avx tpsd106m035r0300, esr = 0.3 w c2 avx tpse227m010r0100, esr = 0.1 w d1 motorola mbrs130lt3 l1 coiltronics ctx100-2p, dcr = 0.541 w pgnd 3 12 6 4 10 5 c3 3300pf mbrs130lt3 figure 5. 8vC24v to 5v/0.5a buck converter low-profile surface mount c1 10? 50v d1 ss16 c2 68? 20v l1 250? sgnd fb sw MIC4574bwm shdn 16v to 24v 12v/0.5a v in r2 13.0k 1% r1 1.50k 1% c1 tokin c55y5u1h106z c2 avx tpse686m020r0150, esr = 0.15 w d1 general instruments ss16 l1 coiltronics ctx250-4p, dcr = 0.434 w pgnd 3 12 6 4 10 5 c3 3300pf figure 6. 16vC24v to 12v/0.5a buck converter low-profile surface mount
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