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mic24085 18v, 3a, 1mhz, high - performance, integrated fet buck regulator in tiny 3mm 3mm qfn micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel +1 (408) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com october 22 , 2013 revision 1.1 general description micrels mic24085 is a constant - frequency, current - mode pwm buck regulator with integrated switchers. the mic24085 is targeted for cost - sensitive and high - performance applications. the mic24085 operates over a supply range of 4.5v to 18v at a fixed 1mhz switching frequency and can be used to provide up to 3a of output current. the output voltage is adjustable down to 0.9v. the mic24085 provides the feat ures of low standby current at 1 0 a, device enable, input under voltage lockout, and output voltage monitoring. the part also pro vides fault protections of overcurrent and over temperature. the mic24085 is available in a 16 - pin 3mm 3mm qfn package with a j unction operating range from C 40 c to +125 c. datasheets and support documentation are available on micrels web site at : www.micrel.com . features ? input voltage range 4.5v to 18v ? 3a output current ? 1mhz switching freq uency ? 0.9v reference voltage with 1.5% accuracy ? fixed output voltages are available at: 1.5v/1.8v/2.5v/3.3v/5v ? peak current - mode pwm with internal compensation ? pfm mode for light load efficiency ? 10 a typical shutdown current ? 4ms internal soft start ? cycle - by - cycle current limit with frequency foldback ? output overvoltage protection ? enable input/power - good (pg) output ? thermal - shutdown protection ? C 40 c to +125 c junction temperature range ? available in 16 - pin 3mm 3mm qfn package applications ? camera, s et - top box, gateways, and routers ? networking/t elecom infrastructure ? pr inters, scanners, graphic cards, and video cards typical application s
micrel, inc. mic24085 october 22 , 2013 2 revision 1.1 ordering information part number output voltage junction temperature range package lead finish mic2 4085a ym l adj C 40 c to +125c 1 6 -p in 3mm x 3mm qfn pb - free mic24085byml 1.5v mic24085 c yml 1.8v mic24085 d yml 2.5v mic24085 e yml 3.3v mic24085 f yml 5v pin configuration 16- pin 3mm 3mm qfn (ml) (top view) pin description pin number pin name pin function 1, 12, 13, 16 sw switch node (output): power stage output. connect an inductor to this pin. 2, 3, 11 vcc supply voltage (for control circuit and power stage): a ceramic input capacitor between v cc and the power ground (pgnd ) is required . 4 gnd analog ground: gnd is the ground path of the control circuitry. 5 fb feedback (i nput): input to the error amplifier of the pwm control ler . the fb pin is regulated to 0. 9 v. a resistor divider connecting the feedback to the output is used to adjust th e desired output voltage . 6, 7 nc no connection. 8 pg power good (output): open drain o utput , which needs a pull -up. the pg pin turns logic high when the converter output voltage is regulated in the range from 93 % to 103 % of the setting. 9 en enable (i nput): an accurate enable with hysteresis is provide d . high = enable, low = shutdown. enable has an internal pull - up to ensure a stable state if this pin is not connected. 10 bst boost (o utput): bootstrapped voltage to the high - side n - channel mosfet. a bo ost capacitor of 0.1f is connected between the bst pin and the sw pin . 14,15 pgnd power ground: pgnd is the ground path for the power stage . ep epad exposed pad. it must be connected to pgnd on the pcb.
micrel, inc. mic24085 october 22 , 2013 3 revision 1.1 absolute maximum ratings ( 1 ) v vcc to p gnd ................................................ ? 0.3v to + 20 v v sw to p gnd ................................................. ? 0.3v to + 20 v v en , v fb , v pg, to gnd ..................................... ? 0.3v to + 6 v v bst to v sw ..................................................... ? 0.3v to + 6 v v bst to pgnd ................................................ ? 0.3v to +26 v pgnd t o gnd ............................................. ? 0.3v to + 0.3v junction temperature .............................................. +150 c storage temperature (t s ) ......................... ? 65 c to +150 c lead temperature (soldering, 10sec) ........................ 260 c esd rating ( 3) .................................................................. 2 kv operating ratings ( 2 ) supply voltage ( v vcc ) ....................................... 4.5 v to 18 v output current ................................................................ 3a junction temperature (t j ) ........................ ? 40 c to +125 c junction thermal resistance mlf - 16 ( ja ) ..................................................... 6 8c/w mlf - 16 ( jc ) .................................................... 7.5 c/w electrical characteristics ( 4 ) v vcc = 12v; t a = 25 c, unless noted. bold values indicate ? 4 0 c t j +12 5 c. parameter condition min. typ. max. units power supply input v cc input voltage range 4.5 18 v quiescent supply current no switching, v fb = 1.5v 2.3 ma shutdown supply current v en = 0v 5 10 a v cc uvlo threshold 4.3 4.5 v v cc uvlo hysteresis 650 mv reference (mic24085ayml) feedback reference voltage -4 0 c t j +125 c ( 1.5%) 0.886 0.9 0.914 v fb bias current v fb = 0.6v 50 500 na soft - start time 4 m s load regulation i out = 100ma to 3 a 0.5 % line regulation v vcc = 4.5v to 18 v 0.5 % enable control en logic level high 2.2 v en logic level low 0.8 v en hysteresis 480 mv en bias current v en = 5v 3.5 a v en = 0v - 1.5 pwm switching frequency v fb = 0.9v 0.9 1.0 1.1 mhz foldback switching frequency v fb < 60% 0.9v 250 khz maximum duty cycle v fb = 0v, 1mhz 97 % minimum duty cycle v fb = 1v 0 % notes: 1. exceeding the absolute maximum ratings may damage the device. 2. the device is not guaranteed to function outside its operating ratings. 3. devices are esd sensitive. handling precautions are recommended. human body model, 1.5k in series with 100pf. 4. specification for pa ckaged product only.
micrel, inc. mic24085 october 22 , 2013 4 revision 1.1 electrical characteristics ( 4 ) (continued) v vcc = 12v; t a = 25 c, unless noted. bold values indicate ? 4 0 c t j +12 5 c. parameter condition min. typ. max. units internal mosfet high side on - resistance i sw = 1a 135 m low side on - resistance i sw = 1a 90 m overcurrent protection current - limit threshold v fb = 0.9v 3.4 3.8 4.4 a power good power good threshold voltage sweep v fb from low -to - high 91 93 95 % v out power good hysteresis sweep v fb from high -to - low 1.5 % v out power good low voltage v fb < 90% x v nom , i pg = - 0.3ma 50 100 mv power good recovery hold time pg recovery after power restoration 9 11 12 ms thermal protection overtemperature shutdown t j rising 170 c overtemperature shutdown hysteresis 10 c
micrel, inc. mic24085 october 22 , 2013 5 revision 1.1 typical characteristics t j = ? 40 c to +125 c, v cc = 12v (unless otherwise noted).
micrel, inc. mic24085 october 22 , 2013 6 revision 1.1 typical characteristics (continued) t j = ? 40 c to +125 c, v cc = 12v (unless otherwise noted).
micrel, inc. mic24085 october 22 , 2013 7 revision 1.1 functional characteristics t j = ? 40 c to +125 c, v cc = 12v (unless otherwise noted).
micrel, inc. mic24085 october 22 , 2013 8 revision 1.1 functional diagram
micrel, inc. mic24085 october 22 , 2013 9 revision 1.1 functional description micrel s mic24085 is a n 18v, 3 a, 1mhz buck r egulator w ith integrated mosfetss for low - c ost high - performance applications. the mic24085 provides basic features including enable, power goo d, internal soft - start, current - limit, and over temperature protections. vcc sup ply voltage and uvlo the mic24085 is held in the off state until vcc reaches the uvlo threshold, which has a 650mv hysteresis. a ceramic capacitor from vcc to pgnd is recommended for clean operation . enable and soft - s tart when the mic24085 is enabled, the referenc e voltage is controlled to ramp - up from 0v to 0.9v in approximately 4ms. during the soft - start, the current limit is enabled to protect the device in case of a short circuit present at the output. peak current - mode pwm t o achieve fast transient response, t he peak current - mode pwm con trol is employed in the mic24085 . as illustrated in the functional diagram , the high - side mosfet current ( isw ) is se nsed and summed with a slope - compensating ramp. then it is compared with the error amplifier output to generate a pwm signal. the loop compensation is designed internally in the mic24085 to ensure loop s tability, even with a low - esr capacitor at the outpu t, such as a ceramic output capacitor. pfm mode at light l oad the mic24085 runs in asynchronous buck mode at light load, where the bottom mosfet is turned off when the inductor current drops to zero. this scheme prevents the output energy from being pumped back to the input, and improves the over - all efficiency. current limit and frequency foldback in the mic24085 isw is also used to determine over - current conditions. as the peak inductor current is limited, the output voltage of the buck converter drops as the load current increases. when the output voltage reaches 60% of regulated voltage (or feedback voltage reaches 60% of 0.9v), the switching frequency is forced to fold back, fr om 1mhz to 250khz. this current - limit scheme reduces the average inductor current (even with the same peak inductor current), and improves th e power consumption at the over load conditions. the current limit is always active when the regulator is en abled. once the over current condition is removed, the device runs to a soft - start and returns to a normal operation. power good (pg) power good (pg) is an open drain o utput pin. a 10k resistor to vout is required for pull - up. the pg pin turns low if the output voltage is below 93% of the reference voltage (0.9v). after vout fault and r ecovery, pg is held low for a typical duration of 11ms. see the electrical characteristics table for additional information. channel 1: vout, channe l 2: pg, hold time: 11ms output voltage protection the mic24085 turns both high - side and low - sid e mosfets off to shut down the buck r egulator output voltage when the output voltage exceeds 103% of the regulated voltage. after the output voltage drops back below the threshold, the mic24085 runs to a soft - start . thermal shutdown the mic24085 turns both high - side and low - side mosfets off t o shut down the buck r egulator output voltage when the internal temperature is over the setting threshold at around 170 c. after the temperature drops back below the threshold, the mic24085 runs to a soft - start .
micrel, inc. mic24085 october 22 , 2013 10 revision 1.1 transient response and control loop bandwidth mic24085 with adjustable output voltage has been designed to work under a wide range of input and output voltages, supporting different values and types of output capacitance. by design, the mic24085 has a lower control loop bandwidth. for design s with aggressive load step response requirements, using a fixed - output voltage version with a larger output capacitance is recommended. adjustable output voltage : v in = 12v, v out = 5v, load step = 0.5a to 2.5a at 50ma/ s with 1x470 f and 1x100 f outpu t capacitance. channel 1: vout, channel 2: pg, channel 3: load step
micrel, inc. mic24085 october 22 , 2013 11 revision 1.1 evaluation board schematic bill of materials item part number manufacturer description qty. c1 grm31cr61e106ka12 murata (5) 10f/25v ceramic capacitor, x5r, size 1206 1 c2, c5 grm188r71h104ka93d murata 0.1f/50v ceramic capacitor, x7r, size 0603 2 c3 grm31cf51a226ze01l murata 22f/10v ceramic capacitor, x5r, size 1206 1 c4 (open) murata 22f/10v ceramic capacitor, x5r, size 1206 1 d1 (open) sk33a diodes, inc. (6) 40v small signal schottky diode, sod123 1 l1 cip0530lr3r3 abc taiwan electr onics corporation (7) 3.3h inductor, 5a sat. current 1 r1, r4 crcw06033k32fkea vishay dale (8) 3.32k resistor, size 0603, 1% 1 r2, r8 crcw060310k0fkea vishay dale 10k resistor, size 0603, 1% 2 r3 crcw06034k99fkea vishay dale 4.99k resistor, size 0603, 1% 1 r5 crcw06031k87fkea vishay dale 1.87k resistor, size 0603, 1% 1 r6 crcw06031k24fkea vishay dale 1.24k resistor, size 0603, 1% 1 r7 crcw0603732r0fkea vishay dale 732 resistor, size 0603, 1% 1 u1 mic24085ayml micrel inc. (9) 18v, 3a, 1mhz tiny buck regulator 1 notes: 5. murata : www.murata.com . 6. diodes, inc. : www.diodes.com . 7. abc taiwan electronics corporation : www.atec - group.com . 8. vishay: www.vishay.com . 9. micrel, inc.: www.micrel.com .
micrel, inc. mic24085 october 22 , 2013 12 revision 1.1 pcb layout recommendations recommended component p lacement at top layer
micrel, inc. mic24085 october 22 , 2013 13 revision 1.1 pcb layout recommendations (continued) top layer mid - layer 1 (ground plane)
micrel, inc. mic24085 october 22 , 2013 14 revision 1.1 pcb layout recommendations (continued) mid - layer 2 (ground plane) bottom layer (ground p lane)
micrel, inc. mic24085 october 22 , 2013 15 revision 1.1 package information ( 10) and recommended landing pattern 16- pin 3mm 3mm qfn (ml ) note: 10. package information is correct as of the publication date. for updates and most current information, go to www.micrel.com .
micrel, inc. mic24085 october 22 , 2013 16 revision 1.1 micrel, inc. 2180 fortune drive san jose, ca 95131 usa tel +1 (408) 944 - 0800 fax +1 (408) 474- 1000 web http://www.micrel.com micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in th is data sheet. this information is not intended as a warranty and micrel does not assume responsibility for its use. micrel reserves the right to change circuitry, specifications and descriptions at any time without notice. no license, whether express, implied, arising by estoppel or otherwise, to any intellectual property rights is granted by this document. except as provided in micrels terms and conditions of sale for such products, micrel assumes no liability whatsoever, and micrel disclaims any express or implied warranty relating to the sale and/or use of micrel products including liability or warrantie s relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right . micrel products are not designed or authorized for use as components in life support appliances, devices or sys tems where malfunction of a product can reasonably be expected to result in personal injury. life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure t o perform can be reasonably expected to result in a significant injury to the user. a purchasers use or sale of micrel products for use in life support appliances, devices or systems is a purchasers own risk a nd purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 20 13 micrel, incorporated.

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