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MIC45208 - 1/ - 2 26v 10a dc - to - dc power module hyper speed control is a trademark of micrel, inc . hyperlight load is a registered trademark of micrel, inc. micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel +1 (408) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com may 29 , 2014 revision 1. 2 general description micrels MIC45208 is a synchronous step - down regulator module, featuring a unique adaptive on - time control architecture. the module incorporates a dc - to - dc controller, power mosfets, bootstrap diode, bootstrap capacitor, and an induct or in a single package; simplifying the design and layout process for the end user. this highly - integrated solution expedites system design and improves product time - to - market. the internal mosfets and inductor are optimized to achieve high efficiency at a low output voltage. the fully - optimized design can deliver up to 10a current under a wide input voltage range of 4.5v to 26v, without requiring additional cooling. the MIC45208 - 1 uses micrels hyperlight load ? (hll) while the MIC45208 - 2 uses micrels hyp er speed control ? (hsc) architecture, which enables ultra - fast load transient response, allowing for a reduction of output capacitance. the MIC45208 offers 1% output accuracy that can be adjusted from 0.8v to 5.5v with two external resistors. additional f eatures include thermal shutdown protection, input undervoltage lockout, adjustable current limit, and short circuit protection. the MIC45208 allows for safe start - up into a pre - biased output. datasheet and other support documentation can be found on micr els web site at: www.micrel.com . features ? no compensation required ? up to 10a output current ? >93% peak efficiency ? output voltage: 0.8v to 5.5v with 1% accuracy ? adjustable switching frequency from 200khz to 600khz ? enable input and open - drain power good (pg) output ? hyper speed control ( MIC45208 - 2) architecture enables fast transient response ? hyperlight load ( MIC45208 - 1) improves light load efficiency ? supports safe startup into pre - biased output ? cispr22, class b comp liant ? C 40 ? c to +125 ? c junction temperature range ? thermal - shutdown protection ? short - circuit protection with hiccup mode ? adjustable current limit ? available in 52 - pin 10 mm 10 mm 4mm qfn package applications ? high power density point - of - load conversion ? serve rs, routers, networking, and base stations ? fpgas, dsp, and low - voltage asic power supplies ? industrial and medical equipment typical application 10 20 30 40 50 60 70 80 90 100 0 2 4 6 8 10 12 14 efficiency (%) output current (a) efficiency (v in = 12v) vs. output current (MIC45208 - 1) f sw = 600khz 5.0v out 3.3v out 2.5v out 1.8v out 1.5v out 1.0v out 0.8v out 1.2v out
micrel, inc. MIC45208 may 29 , 2014 2 revision 1. 2 ordering information part number switching f requency features junction temp erature range package ( 1 ) lead finish MIC45208 - 1 ym p 2 00khz to 600khz hyper light load C 40c to +125c 52 - pin 10mm 10mm 4mm qfn pb - free MIC45208 - 2ymp 200khz to 600khz hyper speed control C 40c to +125c 52 - pin 10mm 10mm 4mm qfn pb - free note: 1. qfn is a lead - free package. lead - free lead finish is matte tin. pin configuration 52 - pin 10mm 10mm qfn (mp) (top view)
micrel, inc. MIC45208 may 29 , 2014 3 revision 1. 2 pin description MIC45208 pin number pin name pin function 1, 2 5vdd internal +5v linea r regulator output. powered by vin, 5vdd is the internal supply bus for the device. in the applications with vin<+5.5v, 5 vdd should be tied to vin to by pass the lin ear regulator. 3, 4 pvdd pvdd: supply input for the internal low - side power mosfet driver. 5, 6, 7 pgnd power ground. pgnd is the return path for the step - down power module power stage. the pgnd pin connects to the sources of internal low - side power mosfet, the negative terminals of input capacitors, and the negative terminals of output capacit ors. 8 ? 11 30 ? 36 sw the sw pin connects directly to the switch node. due to the high - speed switching on this pin, the sw pin should be routed away from sensitive nodes. the sw pin also senses the current by monitoring the voltage across the low - side mo sfet during off time. 12 ? 19 pvin power input voltage: connection to the drain of the internal high side power mosfet. connect an input capacitor from pvin to pgnd. 20 ? 29 vout power output voltage: connected to the internal inductor, the output capaci tor should be connected from this pin to pgnd as close to the module as possible. 37, 38 ria ripple injection pin a. leave floating, no connect ion . 39 rib ripple injection pin b. connect this pin to fb . 40, 41 anode anode bootstrap diode: anode connec tion of internal bootstrap diode, this pin should be connected to the pvdd pin. 42, 43, 44 bst connection to the internal bootstrap circuitry and high side power mosfet drive circuitry. leave floating, no connect ion . 45, 52 gnd analog ground. connect bo ttom feedback resistor to gnd. gnd and pgnd should be connected together at a low impedance point. 46 fb feedback: input to the transconductance amplifier of the control loop. the fb pin is referenced to 0.8v. a resistor divider connecting the feedback to the output is used to set the desired output voltage. connect the bottom resistor from fb to gnd. 47 pg power good: open drain output. if used, connect to an external pull - up resistor of at least 10kohm between pg and the external bias voltage. 48 en en able: a logic signal to enable or disable the step - down regulator module operation. the en pin is ttl/cmos compatible. logic high = enable, logic low = disable or shu tdown. do not leave floating 49 vin internal 5v linear regulator input. a 1f ceramic capacitor from vin to gnd is required for decoupling. 50 freq switching frequency adjust: use a resistor divider from vin to gnd to program the switching frequency. connecting freq to vin sets freq=600khz. 51 ilim current limit: connect a resistor between ilim and sw to program the current limit.
micrel, inc. MIC45208 may 29 , 2014 4 revision 1. 2 absolute maximum ratings ( 2 ) v pvin , v vin to pgnd ................................ ....... ? 0.3v to +30v v pvdd , v 5vdd , v anode to pgnd ......................... ? 0.3v to +6v v sw , v fre q , v ilim , v en to pgnd ............ ? 0.3v to (v in +0.3v) v bst to v sw ................................ ........................ ? 0.3v to 6v v bst to pgnd ................................ .................. ? 0.3v to 36v v pg to pgnd ................................ .. ? 0.3v to ( 5 v dd + 0.3v) v fb , v rib to pgnd .......................... ? 0.3v to ( 5 v dd + 0.3v) pgnd to gnd ................................ .............. ? 0.3v to +0.3v junction temperature ................................ .............. +150c storage temperature (t s ) ......................... ? 65 ? c to +150 ? c lead temperature (soldering, 10s) ............................ 260c esd rating.esd sensitive operating ratings ( 3 ) supply voltage ( v pvin , v v in ) .............................. 4. 5 v to 26v output current ................................ ............................... 10a enable input (v en ) ................................ .................. 0v to v in power good (v pg ) ................................ ............. 0v to 5 v dd junction temperature (t j ) ........................ ? 40 ? c to +125 ? c junction thermal resistance ( 4 ) 10 mm 10 mm 4mm qfn - 52 ( ? ja ) ............ 16.6 c/w 10 mm 10 mm 4mm qfn - 52 ( ? jc ) ................. 4 c/w electrical characteristics ( 5 ) v pin = v in = v en = 12v, v out = 3.3v, v bst ? v sw = 5v, t j = +25oc. bold values indicate ? 40oc ? t j ? +125oc, unless otherwise noted. parameter condition min . typ . max . units power supply input input voltage range (v p v in , v in ) 4.5 26 v quiescent supply current ( MIC45208 - 1) v fb = 1.5v 0.75 ma quiescent supply current ( MIC45208 - 2) v fb = 1.5v 2.1 3 ma operating current v pv in = v in = 12v, v out = 1.8v, i out = 0a, f sw = 600khz MIC45208 - 1 0.4 m a MIC45208 - 2 43 shutdown supply current sw = u nconnected, v en = 0v 4 10 a 5vdd output 5vdd output voltage v in = 7v to 26v, i 5vdd = 10ma 4.8 5.1 5.4 v 5vdd uvlo threshold v 5vdd rising 3.8 4.2 4.6 v 5vdd uvlo hysteresis v 5vdd falling 400 mv ldo load regulation i 5vdd = 0 to 40ma 0.6 2 3.6 % reference feedback reference voltage t j = 25 c 0.792 0.8 0.808 v ? j 125 0.784 0.8 0.816 fb bias current v fb = 0.8v 5 500 na enable control en logic level high 1.8 v en logic level low 0.6 v en hysteresis 200 mv en bias current v en = 12v 5 10 a notes: 2. exceeding the absolute maximum ratings may d amage the device. 3. the device is not guaranteed to function outside operating range. 4. ? ja and ? jc were measured using the mic 45208 evaluation board. 5. specification for packaged product only.
micrel, inc. MIC45208 may 29 , 2014 5 revision 1. 2 electrical characteristics ( 5 ) (continued) v pin = v in = v en = 12v, v out = 3.3v, v bst ? v sw = 5v, t j = +25oc. bold values indicate ? 40oc ? t j ? +125oc, unless otherwise noted. parameter condition min . typ . max . units oscillator switching frequency v freq = v i n , i out = 2a 400 600 750 khz v freq = 50%v i n , i out = 2a 350 maximum duty cycle 85 % minimum duty cycle v fb = 1v 0 % minimum off - time 140 200 260 ns soft - start soft - start time 3 ms short - circuit protection current - limit threshold v fb = 0.79v ? ? fb = 0v ? ? fb = 0.79v 50 70 90 a short - circuit source current v fb = 0v 25 35 45 a leakage sw, bst leakage current 10 a freq leakage current 10 a power good (pg) pg thresh old voltage sweep v fb from low - to - high 85 90 95 % v out pg hysteresis sweep v fb from high - to - low 6 % v out pg delay time sweep v fb from low - to - high 100 s pg low voltage v fb < 90% v nom , i pg = 1ma 70 200 mv thermal protection overtemperature shutdow n t j rising 160 c overtemperature shutdown hysteresis 1 5 c
micrel, inc. MIC45208 may 29 , 2014 6 revision 1. 2 typical characteristics 300 400 500 600 700 800 900 -50 -25 0 25 50 75 100 125 switching frequency (khz) temperature ( c) switching frequency vs. temperature v in = 12v v out = 1.8v i out = 2a 1.5 1.6 1.7 1.8 1.9 2.0 2.1 -50 -25 0 25 50 75 100 125 output voltage (v) temperature ( c) output voltage vs. temperature v in = 12v v out = 1.8v i out = 0a 0.5 0.6 0.7 0.8 0.9 1.0 1.1 -50 -25 0 25 50 75 100 125 feeback voltage (v) temperature ( c) feedback voltage vs. temperature v in = 12v v out = 1.8v i out = 0a 0 2 4 6 8 10 -50 -25 0 25 50 75 100 125 en bias current (a) temperature ( c) en bias current vs. temperature v in = 12v v out = 1.8v i out = 0a 0.0 0.4 0.8 1.2 1.6 2.0 -50 -25 0 25 50 75 100 125 enable threshold (v) temperature ( c) enable threshold vs. temperature falling rising v in = 12v v out = 1.8v 0 120 240 360 480 600 -50 -25 0 25 50 75 100 125 supply current (a) temperature ( c) vin operating supply current vs. temperature (MIC45208 - 1) v in = 12v v out = 1.8v i out = 0a 0 2 4 6 8 10 -50 -25 0 25 50 75 100 125 vdd supply voltage (v) temperature ( c) vdd supply voltage vs. temperature v in = 12v v out = 1.8v i out = 0a 0 20 40 60 80 100 -50 -25 0 25 50 75 100 125 supply current (ma) temperature ( c) vin operating supply current vs. temperature (MIC45208 - 2) v out = 1.8v i out = 0a f sw = 600khz 0 10 20 30 40 50 4.5 8.8 13.1 17.4 21.7 26 shutdown current (a) input voltage (v) vin shutdown current vs. input voltage v en = 0v r10 = open
micrel, inc. MIC45208 may 29 , 2014 7 revision 1. 2 typical characteristics (continued) 10 20 30 40 50 60 70 80 90 100 0 2 4 6 8 10 12 14 efficiency (%) output current (a) efficiency (v in = 12v) vs. output current (MIC45208 - 1) f sw = 600khz 5.0v out 3.3v out 2.5v out 1.8v out 1.5v out 1.0v out 0.8v out 1.2v out 10 20 30 40 50 60 70 80 90 100 0 2 4 6 8 10 12 14 efficiency (%) output current (a) efficiency (v in = 5v) vs. output current (MIC45208 - 1) f sw = 600khz 3.3v out 2.5v out 1.8v out 1.5v out 1.0v out 0.8v out 1.2v out 0 2 4 6 8 10 12 14 16 18 20 -50 -25 0 25 50 75 100 125 current limit (a) temperature ( c) output peak current limit vs. temperature v in =12v v out = 1.8v f sw = 600khz r lim = 1.07k 10 20 30 40 50 60 70 80 90 100 0 2 4 6 8 10 12 14 efficiency (%) output current (a) efficiency (v in = 24v) vs. output current (MIC45208 - 1) f sw = 600khz 5.0v out 3.3v out 2.5v out 1.8v out 1.5v out 1.0v out 0.8v out 1.2v out 10 20 30 40 50 60 70 80 90 100 0 2 4 6 8 10 12 14 efficiency (%) output current (a) efficiency (v in = 24v) vs. output current (MIC45208 - 2) f sw = 600khz 5.0v out 2.5v out 1.8v out 1.5v out 1.0v out 0.8v out 1.2v out 3.3v out 10 20 30 40 50 60 70 80 90 100 0 2 4 6 8 10 12 14 efficiency (%) output current (a) efficiency (v in = 12v) vs. output current (MIC45208 - 2) f sw = 600khz/200khz 5.0v out 2.5v out 1.8v out 1.5v out 1.0v out 0.8v out 1.2v out 3.3v out 10 20 30 40 50 60 70 80 90 100 0 2 4 6 8 10 12 14 efficiency (%) output current (a) efficiency (v in = 5v) vs. output current (MIC45208 - 2) f sw = 600khz 2.5v out 1.8v out 1.5v out 1.0v out 0.8v out 1.2v out 3.3v out 1.50 1.55 1.60 1.65 1.70 1.75 1.80 1.85 1.90 1.95 2.00 0.00 2.00 4.00 6.00 8.00 10.00 12.00 vout(v) output current (a) load regulation vs. input voltage v out = 1.8v 1.5 1.6 1.7 1.8 1.9 2.0 2.1 4.5 8.8 13.1 17.4 21.7 26.0 output voltage (v) input voltage (v) line regulation v out = 1.8v i out = 10a
micrel, inc. MIC45208 may 29 , 2014 8 revision 1. 2 typical characteristics (continued) 0 0.5 1 1.5 2 2.5 3 3.5 0 2 4 6 8 10 12 14 ic power dissipation (w) output current (a) ic power dissipation (v in = 5v) vs. output current v in = 5v f sw = 600khz 3.3v out 2.5v out 1.8v out 1.5v out 1.0v out 0.8v out 1.2v out 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 2 4 6 8 10 12 14 ic power dissipation (w) output current (a) ic power dissipation (v in = 12v) vs. output current v in = 12v f sw = 600khz 3.3v out 2.5v out 1.8v out 1.5v out 1.0v out 0.8v out 1.2v out 5.0v out 0 1 2 3 4 5 6 7 8 0 2 4 6 8 10 12 14 ic power dissipation (w) output current (a) ic power dissipation (v in = 24v) vs. output current v in = 24v f sw = 600khz 3.3v out 2.5v out 1.8v out 1.5v out 1.0v out 0.8v out 1.2v out 5.0v out
micrel, inc. MIC45208 may 29 , 2014 9 revision 1. 2 functional characteristics
micrel, inc. MIC45208 may 29 , 2014 10 revision 1. 2 functional characteristics (continued)
micrel, inc. MIC45208 may 29 , 2014 11 revision 1. 2 functional characteristics (continued)
micrel, inc. MIC45208 may 29 , 2014 12 revision 1. 2 functional diagram
micrel, inc. MIC45208 may 29 , 2014 13 revision 1. 2 f unctional description the MIC45208 is an adaptive on - time synchronous buck regulator module built for high - input voltage to low - output voltage conversion applications. the MIC45208 is designed to operate over a wide input voltage range, from 4.5v to 26v, a nd the output is adjustable with an external resistor divider. an adaptive on - time control scheme is employed to obtain a constant switching frequency in steady state and to simplify the control compensation. hiccup mode over - current protection is implemen ted by sensing low - side mosfets r ds(on) . the device features internal soft - start, enable, uvlo, and thermal shutdown. the module has integrated switching fets, inductor, bootstrap diode, resistor, capacitor, and controller. theory of operation as shown in figure 1 , in association with equation 1 , the output voltage is sensed by the MIC45208 feedback pin fb via the voltage divider r fb 1 and r fb 2 , and compared to a 0.8v reference voltage , v ref , at the error comparator through a low - gain transconductance (g m ) amplifier. if the feedback voltage decreases and falls below 0.8v, then the error comparator will trigger the control logic and generate an on - time period. the on - time period length is predetermined by the fixed t on estimator circuitry: figure 1 . output voltage sense via fb pin eq. 1 where v out is the output voltage, v in is the power stage input voltage, and f sw is the switching frequency. at the end of the on - time period, the internal high - side driver turns off the high - side mosfet and the low - side driver turns on the low - side mosfet. the off - time period length depends upon the feedback voltage in most cases. when the feedback voltage decreases and the output of the g m amplifier falls below 0.8v, the on - time period is triggered and the off - time period ends. if the off - time period determined by the feedback voltage is less than the minimum off - time t off(min) , which is about 200ns, the MIC45208 control logic will apply the t off(min) instead. t off(min) is required to maintain enough energy in the boost capacitor (c bst ) to drive the high - side mosfet. the maximum duty cycle is obtained from the 200ns t off(min ) : eq. 2 where: t s = 1/f sw . it i s not recommended to use MIC45208 with an off - time close to t off(min) during steady - state operation. the adaptive on - time control scheme results in a constant switching frequency in the MIC45208 during steady state operation . also, the minimum t on results in a lower switching frequency in high v in to v out applications. during load transients, the switching frequency is changed due to the varying off - time. to illustrate the control loop operation, we will analyze both the steady - state and load transient sc enarios. for easy analysis, the gain of the g m amplifier is assumed to be 1. with this assumption, the inverting input of the error comparator is the same as the feedback voltage. figure 2 shows the MIC45208 contr ol loop timing during steady - state operation. during steady - state, the g m amplifier senses the feedback voltage ripple, which is proportional to the output voltage ripple plus injected voltage ripple, to trigger the on - time period. the on - time is predeterm ined by the t on estimator . the termination of the off - time is controlled by the feedback voltage. at the valley of the feedback voltage ripple, which occurs when v f b falls below v ref , the off period ends and the next on - time period is triggered through the control logic circuitry. sw in o ut ) esti m ated ( on f v v t ? ? s s ) m i n ( o ff s m ax t ns 200 1 t t t d ? ? ? ?
micrel, inc. MIC45208 may 29 , 2014 14 revision 1. 2 figure 2 . MIC45208 control loop timing figure 3 shows the operation of the MIC45208 during a load transient. the output voltage drops due to the sudden load in crease, which causes the v fb to be less than v ref . this will cause the error comparator to trigger an on - time period. at the end of the on - time period, a minimum off - time t off(min ) is generated to charge the bootstrap capacitor (c bst ) since the feedback vo ltage is still below v ref . then, the next on - time period is triggered due to the low feedback voltage. therefore, the switching frequency changes during the load transient, but returns to the nominal fixed frequency once the output has stabilized at the ne w load current level. with the varying duty cycle and switching frequency, the output recovery time is fast and the output voltage deviation is small. note that the instantaneous switching frequency during load transient remains bounded and cannot increase arbitrarily. the minimum is limited by t on + t off (min) .since the variation in v out is relatively limited during load transient, t on stays virtually close to its steady - state value. figure 3 . MIC45208 load transient response unlike true current - mode control, the MIC45208 uses the output voltage ripple to trigger an on - time period. the output voltage ripple is proportional to the inductor current ripple if the esr of the output capacitor is large enough. in order to meet the st ability requirements, the MIC45208 feedback voltage ripple should be in phase with the inductor current ripple and are large enough to be sensed by the g m amplifier and the error comparator. the recommended feedback voltage ripple is 20mv~100mv over full i nput voltage range. if a low esr output capacitor is selected, then the feedback voltage ripple may be too small to be sensed by the g m amplifier and the error comparator. also, the output voltage ripple and the feedback voltage ripple are not necessarily in phase with the inductor current ripple if the esr of the output capacitor is very low. in these cases, ripple injection is required to ensure proper operation. please refer to ripple injection subsection in th e application information section for more details about the ripple injection technique. discontinuous mode ( MIC45208 - 1 only) in continuous mode , the inductor current is always greater than zero; however, at light loads , the MIC45208 - 1 is able to force the inductor current to operate in discontinuous mode. discontinuous mode is where the inductor current falls to zero , as indicated by trace (i l ) shown in figure 4 . during thi s period , the efficiency is optimized by shutting down all the non - essential circuits and minimizing the supply current as the switching frequency is reduced . the MIC45208 - 1 wakes up and turns on the high - side mosfet when the feedback voltage v fb drop s bel ow 0.8v. the MIC45208 - 1 has a zero c ross ing c omparator (zc) that monitors the inductor current by sensing the voltage drop across the low - side mosfet during its on - time. if the v fb > 0.8v and the inductor current goes slightly negative, then the MIC45208 - 1 automatically powers down most of the ic circuitry and goes into a low - power mode. once the MIC45208 - 1 goes into discontinuous mode, both dl and dh are low, which turns off the high - side and low - side mosfets. the load current is supplied by the output ca pacitors and v out drops. if the drop of v out causes v fb to go below v ref , then all the circuits will wake up into normal continuous mode. first , the b ias currents of most circuits reduced during the discontinuous mode are restored, and then a t on pulse is triggered before the drivers are turned on to avoid any possible glitches. finally, the high - side driver is turned on. figure 4 shows the control loop timing in discontinuous mode.
micrel, inc. MIC45208 may 29 , 2014 15 revision 1. 2 figure 4 . MIC45208 - 1 control loop timing (discontinuous mode) during discontinuous mode, the bias current of most circuits is substantially reduced. as a result, the total power supply current during discontinuous mode is only about 350 a , allowing the mic452 08 - 1 to achieve high efficiency in light load applications. soft - start soft - start reduces the input power supply surge current at startup by controlling the output voltage rise time. the input surge appears while the output capacitor is charged up. the mi c45208 implements an internal digital soft - start by making the 0.8v reference voltage v ref ramp from 0 to 100% in about 4 ms with 9.7mv steps . therefore, the output voltage is controlled to increase slowly by a stair - case v fb ramp. once the soft - start cycle ends, the related circuitry is disabled to reduce current consumption. pv dd must be powered up at the same time or after v in to make the soft - start function correctly. current limit the MIC45208 uses the r ds(on) of the low - side mosfet and external resisto r connected from ilim pin to sw node to set the current limit. figure 5 . MIC45208 current - limiting circuit in each switching cycle of the MIC45208 , the inductor current is sensed by monitoring the low - side mosfet in the off peri od. the sensed voltage v ilim is compared with the power ground (pgnd) after a blanking time of 150ns. in this way the drop voltage over the resistor r15 (v cl ) is compared with the drop over the bottom fet generating the short current limit. the small capac itor (c15) connected from ilim pin to pgnd filters the switching node ringing during the off - time allowing a better short limit measurement. the time constant created by r15 and c6 should be much less than the minimum off time. the v cl drop allows programm ing of short limit through the value of the resistor (r15). if the absolute value of the v oltage drop on the bottom fet becomes greater than v cl, and the v ilim falls below pgnd , an over - current is triggered causing the ic to enter hiccup mode. the hic cup s equence including the soft - start reduces the stress on the switching fets and protects the load and supply for severe short conditions. the short - circuit current limit can be programmed by using equation 3. eq. 3 where: i clim = desi red current limit r ds(on) = on - resistance of low - side power mosfet, 6 m typically . v cl = current - limit threshold (typical absolute value is 14mv per the electrical characteristics table ). i cl = current - limi t source current (typical value is 70 a, per the electrical characteristics table). ? ? cl cl ) on ( ds pp l cli m i v r ) 5 . 0 i i ( r15 ? ? ? ? ? ?
micrel, inc. MIC45208 may 29 , 2014 16 revision 1. 2 i l(pp) = inductor current peak - to - peak, since the inductor is integrated use equation 4 to calculate the inductor ripple current. the peak - to - peak inductor current ripple is: eq. 4 the MIC45208 has a 0 .8 h inductor integrated into the module. in case of a hard short, the short limit is folded down to allow an indefinite hard short on the output witho ut any destructive effect. it is mandatory to make sure that the inductor current used to charge the output capacitance during soft - start is under the folded short limit; otherwise the supply will go in hiccup mode and may not finish the soft - start success fully. the mosfet r ds(on) varies 30% to 40% with temperature; therefore, it is recommended to add a 50% margin to i clim in equation 3 to avoid false current limiting due to increased mosfet junction temperature rise. with r15 = 1. 07 k ? and c15=15pf, the t yp ical output current limit is 16 a. l f v ) v (v v i sw i n( m ax) o ut i n( m ax) o ut l( pp) ? ? ? ? ? ?
micrel, inc. MIC45208 may 29 , 2014 17 revision 1. 2 application information setting the switching frequency the MIC45208 switching frequency can be adjusted by changing the value of resistors r1 and r2. figure 6 . switching frequency adju stment equation 5 gives the estimated switching frequency: eq. 5 where: f o = 600khz (t ypical per electrical characteristics ( 5 ) t able) r1= 100k is recommended. r2 needs to be selected in order to set the required switching frequency. figure 7 . switching frequency vs. r2 the switching frequency also depends upon vin, vout and load cond itions as MIC45208 uses and adaptive on - time architecture as explained in theory of operation. at lower switching frequencies, the i rms c urrent will increase due to higher ripple current. designs need to take this into account when calculating for safe op erating area. output capacitor selection the type of the output capacitor is usually determined by the application and its equivalent series resistance (esr). voltage and rms current capability are two other important factors for selecting the output capa citor. recommended capacitor types are mlcc, os - con and poscap. the output capacitors esr is usually the main cause of the output ripple. the MIC45208 requires ripple injection and the output capacitor esr affects the control loop from a stability point o f view. the maximum value of esr is calculated as in equation 6: eq. 6 where: v out(pp) = peak - to - peak output voltage ripple i l(pp) = peak - to - peak inductor current ripple 2 r 1 r 2 r f f o sw ? ? ? l(pp) out(pp) c i v esr out ? 0 100 200 300 400 500 600 700 800 10.00 100.00 1000.00 10000.00 sw freq (khz) r2 (k ? ) switching frequency v out = 5v vin = 12v r1 = 100k ?
micrel, inc. MIC45208 may 29 , 2014 18 revision 1. 2 the total output ripple is a combination of the esr and output capacitance. the total ripple is calculated in equation 7: eq. 7 wher e: d = duty cycle c out = output capacitance value f sw = switching frequency as described in the theory of operation subsection in the f unctional description , the mic4520 8 requires at least 20mv peak - to - peak ripple at the fb pin to make the g m amplifier and the error comparator behave properly. also, the output voltage ripple should be in phase with the inductor current. therefore, the output voltage ripple caused by the o utput capacitors value should be much smaller than the ripple caused by the output capacitor esr. if low - esr capacitors, such as ceramic capacitors, are selected as the output capacitors, a ripple injection method should be applied to provide enough feedba ck voltage ripple. please refer to ripple injection subsection in the application information section for more details. the output capacitor rms current is calculated in equation 8: eq. 8 the power dissipated in the output capacitor is: eq. 9 input capacitor selection the input capacitor for the power stage input pvin should be selected for ripple curr ent rating and volta ge rating. the input voltage ripple will primarily depend on the input capacitors esr. the peak input current is equal to the peak inductor current, so: v in = i l(pk) esr c in eq. 10 the input capacitor must be rated for the input current ripple. the rms value of input capacitor current is determined at the maximum output current. assuming the peak - to - peak inductor current ripple is low: eq.11 the power dissipated in the input capacitor is: p diss(c in ) = i c in (rms) 2 esr c in eq. 12 the general rule is to pick the capacitor with a ripple current rating equal to or gre ater than the calculated worst case rms capacitor current. equ ation 13 should be used to calculate the input capacitor. also it is recommended to keep some margin on the calculated value: eq. 13 where: dv = the input ripple f sw = s witching frequency ? ? 2 c l(pp) 2 sw out l(pp) out(pp) out esr i 8 f c i v ? ? ? ? ? ? ? ? ? ? ? ? ? 12 i i l(pp) (rms) c o ut ? o ut o ut o ut c 2 ( rm s) c ) di ss( c esr i p ? ? d) (1 d i i out(max) (rms) c in ? ? ? ? dv f ) d 1 ( i c sw out(max) in ? ? ? ?
micrel, inc. MIC45208 may 29 , 2014 19 revision 1. 2 output voltage setting components the mi c45208 requires two resistors to set the output voltage as shown in figure 8 : figure 8 . voltage - divider configuration the output voltage is determined by equation 14: eq. 14 where: v fb = 0.8v a typical value of r fb 1 used on the standard evaluation board is 10k. if r1 is too large, it may allow noise to be introduced into the voltage feedback loop. if r fb 1 is too small in value, it will decrease the efficiency of the power supply, especially at light loads. once r fb 1 is selected, r fb 2 can be calculated using equation 15: eq. 15 for fixed r fb1 = 10k?, output voltage can be selected by r fb2 . table 1 provides r fb2 values for some common output voltages. table 1 . v out programming resistor look - up table r fb2 v out open 0.8v 40.2k ? 1.0v 20k ? 1.2v 11.5k ? 1.5v 8.06k ? 1.8v 4.75k ? 2.5v 3.24k ? 3.3v 1.91k ? 5.0v ripple injection the v fb ripple required for proper operation of the MIC45208 g m amplifier and error comparator is 20mv to 100mv. however, the output voltage ripple is generally too small to provide enough ripple amplitude at the fb pin and this issue is more visible in lower output voltage applications. if the feedback voltage ripple is so small that the g m amplifier and error comparator cannot sense it, then the MIC45208 will lose control and the output voltage is not regulated. in order to have some amount of v fb ripple, a ripple injection method is applied for low ou tput voltage ripple applications. the applications are divided into two situations according to the amount of the feedback voltage ripple: 1. enough ripple at the feedback voltage due to the large esr of the output capacitors: as shown in figure 9 , the converter is stable without any ripple injection. figure 9 . enough ripple at fb from esr ? ? ? ? ? ? ? ? ? ? ? 2 fb 1 fb fb out r r 1 v v fb out fb1 fb fb2 v v r v r ? ? ?
micrel, inc. MIC45208 may 29 , 2014 20 revision 1. 2 the feedback voltage ripple is: eq. 16 where: i l(pp) = the peak - to - peak value of the inductor current ripple 2. there is v irtually no or inadequate ripple at the fb pin voltage due to the very - lo w esr of the output capacitors ; such is the case with ceramic output capacitor. in this case, the v fb ripple waveform needs to be generated by injecting suitable signal. MIC45208 has provisions to enable an internal series rc injection network, r inj and c inj as shown in figure 10 by connecting rib to fb pin. this network injects a square - wave current waveform into fb pin, which by means of integration across the capacitor (c14) generates an ap propriate saw tooth fb ripple waveform. figure 10 . internal ripple injection at fb via rib pin the in jected ripple is: eq.17 eq.18 where: v in = power stage input voltage d = duty cycle f sw = switching frequency ? = (r fb 1 //r fb 2 //r inj ) ? c14 r inj = 10 k ? c inj = 0.1 f in equations 18 and 19, it is assumed that the time constant associated with c14 must be much greater than the switching period: eq. 19 if the voltage divider resistors r fb 1 and r fb 2 are in the k range, then a c14 of 1nf to 100nf can easily satisfy the large time con stant requirements. l(pp) out c fb2 fb1 fb2 fb(pp) i esr r r r v ? ? ? ? ? ? ? ? ? ? ? sw div in fb(pp) f 1 d) - (1 d k v v fb2 fb1 inj fb2 fb1 div //r r r //r r k ? ? 1 t f 1 sw ?? ? ? ? ?
micrel, inc. MIC45208 may 29 , 2014 21 revision 1. 2 thermal measurements and safe operating area (soa) measuring the ics case temperature is recommended to ensure it is within its operating limits. although this might seem like a very elementary task, it is easy to get erroneous resul ts. the most common mistake is to use the standard thermal couple that comes with a thermal meter. this thermal couple wire gauge is large, typically 22 gauge, and behaves like a heatsink, resulting in a lower case measurement. two methods of temperature m easurement are using a smaller thermal couple wire or an infrared thermometer. if a thermal couple wire is used, it must be constructed of 36 - gauge wire or higher (smaller wire size) to minimize the wire heat - sinking effect. in addition, the thermal couple tip must be covered in either thermal grease or thermal glue to make sure that the thermal couple junction is making good contact with the case of the ic. omega brand thermal couple (5sc - tt - k - 36 - 36) is adequate for most applications. wherever possible, a n infrared thermometer is recommended. the measurement spot size of most infrared thermometers is too large for an accurate reading on a small form factor ics. however, an ir thermometer from optris has a 1mm spot size, which makes it a good choice for mea suring the hottest point on the case. an optional stand makes it easy to hold the beam on the ic for long periods of time. the safe operating area (soa) of the MIC45208 is shown in figure 11 , figure 12 , figure 13 , figure 14 , and figure 15 . these thermal measurements were taken on MIC45208 evaluation b oard. since the MIC45208 is an entire system comprised of switching regulator controller, mosfets and inductor, the part needs to be considered as a system. the soa curves will give guidance to reasonable use of the MIC45208 . soa curves should only be used as a point of reference. soa data was acquired using the MIC45208 e valuation board. thermal performance depends on the pcb layout, board size, copper thickness, number of thermal vias, and actual airflow.
micrel, inc. MIC45208 may 29 , 2014 22 revision 1. 2 figure 11 . MIC45208 power derating vs. airflow (5v in to 1.5v out ) figure 12 . MIC45208 power derating vs. airflow (12v in to 1.5v out figure 13 . MIC45208 power derating vs. airflow (12v in to 3.3v out ) figure 14 . MIC45208 power derating vs. airflow (24v in to 1.5v out ) figure 15 . MIC45208 power derating vs. airflow (24v in to 3.3v out ) 4 5 6 7 8 9 10 11 80 85 90 95 100 105 110 115 120 maximum output current (a) ambient temperature ( ? c) 0 lfm 200 lfm 400 lfm 4 5 6 7 8 9 10 11 70 75 80 85 90 95 100 105 110 115 120 maximum output current (a) ambient temperature ( ? c) 0 lfm 200 lfm 400 lfm 4 5 6 7 8 9 10 11 70 75 80 85 90 95 100 105 110 115 120 maximum output current (a) ambient temperature ( ? c) 0 lfm 200 lfm 400 lfm 4 5 6 7 8 9 10 11 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 maximum output current (a) ambient temperature ( ? c) 0 lfm 200 lfm 400 lfm 4 5 6 7 8 9 10 11 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 maximum output current (a) ambient temperature ( ? c) 0 lfm 200 lfm 400 lfm
micrel, inc. MIC45208 may 29 , 2014 23 revision 1. 2 pcb layout guidelines warning: to minimize emi and output noise, follow these layout recommendations. pcb l ayout is critical to achieve reliable, stable and efficient perf ormance. a ground plane is required to control emi and minimize the inductance in power, signal and return paths. figure 16 is optimized from a small form factor point of view shows top and bottom layer of a four - l ayer pcb. it is recommended to use mid layer 1 as a continuous ground plane. figure 16 . top and bottom layer of a four - layer board the following guidelines should be followed to insure proper oper ation of the MIC45208 module: ic ? the analog ground pin (gnd) must be connected directly to the ground planes. place the ic close to the point - of - load (pol). ? use thick traces to route the input and output power lines. ? analog and power grounds should be kept separate and connected at on ly one location with low impedance . input capacitor ? place the input capacitors on the same side of the board and as close to the ic as possible. ? place several vias to the ground plane close to the input capacitor ground terminal. ? use either x7r or x5r die lectric input capacitors. do not use y5v or z5u type capacitors. ? do not replace the ceramic input capacitor with any other type of capacitor. any type of capacitor can be placed in parallel with the ceramic input capacitor. ? if a non - ceramic input capacitor is placed in parallel with the input capacitor, it must be recommended for switching regulator applications and the operating voltage . ? in hot - plug applications, a n e lectrolytic bypass capacitor must be used to limit the over - voltage spike seen on the in put supply with power is suddenly applied. if hot - plugging is the normal operation of the system, using an appropriate hot - swap ic is recommended. rc snubber (optional) ? depending on the operating conditions, a rc snubber on the same side of the board can be used. place the rc and as close to the sw pin as possible if needed. sw node ? do not route any digital lines underneath or close to the sw node. ? keep the switch node (sw) away from the feedback (fb) pin. output capacitor ? use a wide trace to connect the output capacitor ground terminal to the input capacitor ground terminal. ? phase margin will change as the output capacitor value and esr changes. ? the feedback trace should be separate from the power trace and connected as close as possible to the output ca pacitor. sensing a long high - current load trace can degrade the dc load regulation.
micrel, inc. MIC45208 may 29 , 2014 24 revision 1. 2 pcb layout recommendations top ? copper layer 2
micrel, inc. MIC45208 may 29 , 2014 25 revision 1. 2 pcb layout recommendations (continued) copper layer 3 bottom copper layer 4
micrel, inc. MIC45208 may 29 , 2014 26 revision 1. 2 simplified pcb design recommendations periphery i/o pad layout and large pad for exposed heatsink the board design should begin with copper/metal pads that sit beneath the periphery leads of a mounted qfn. the board pads should extend outside the qfn package edge a distance of approximately 0.20 mm per side: total pad length = 10.00mm + (0.20mm per side x 2 sides) = 10.40mm after completion of the periphery pad design, the larger exposed pads will be designed to create the mounting surface of the qfn exposed heats ink. the primary transfer of heat out of the qfn will be directly through the bottom surface of the exposed heatsink. to aid in the transfer of generated heat into the pcb, the use of an array of plated through - hole vias beneath the mounted part is recomme nded. the typical via hole diameter is 0.30mm to 0.35mm, with center - to - center pitch of 0.80 to 1.20mm. . note: exposed metal trace is mirror image of package bottom view . figure 17 . package bottom view vs. pcb recommended exp osed metal trace
micrel, inc. MIC45208 may 29 , 2014 27 revision 1. 2 solder paste stencil design (recommend stencil thickness is 125 25m) the solder stencil aperture openings should be smaller than the periphery or large pcb exposed pads to reduce any chance of build - up of excess solder at the large ex posed pad area which can result to solder bridging. the suggested reduction of the stencil aperture opening is typically 0.20mm smaller than exposed metal trace. the suggested reduction of the stencil aperture opening is typically 0.20mm smaller than e xposed metal trace. note : a critical requirement is to not duplicate land pattern of the exposed metal trace as solder stencil opening as the design and dimension values are different. note: cyan - colored shaded pad indicate exposed trace keep out area . figure 18 . solder stencil opening figure 19 . stack - up of pad layout and solder paste stencil
micrel, inc. MIC45208 may 29 , 2014 28 revision 1. 2 evaluation board schematic bill of materials item part number manufacturer description qty . bj1, bj2 571 - 0500 (red) deltron ( 6 ) con, pcb mount - i nsulated socket 2 bj3, bj4 571 - 0100 (black) deltron con, pcb mount - insulated socket 2 c1 b41851 epcos ( 7 ) 220 f/35v, ale c ap acitor 1 c2, c3 grm32er71h475ka12 murata ( 8 ) 4.7f/50v,x7r,1210,ceramic cap acitor 2 12105c475kaz2a avx ( 9 ) c3225x7r1h475k tdk ( 10 ) c4, c8 grm188r71h104ka93d murata 0.1 f/50v, x7r, 0603, ceramic cap acitor 1 06035c104kat2a avx c1608x7r1h104k tdk notes: 6. deltron: www.deltron.com . 7. epcos: www.epcos.com . 8. murata: www.murata.com . 9. avx: www.avx.com . 10. tdk: www.tdk.com .
micrel, inc. MIC45208 may 29 , 2014 29 revision 1. 2 bill of materials (continued) item part number manufacturer descriptio n qty . c5, c6 12106d107mat2a avx 100f/6.3v, x5r, 1210, ceramic cap acitor 2 grm32er60j107me20l murata c3225x5r0j107m tdk c7, c13 ( open ) c14 c1608c0g1h222jt tdk 2.2nf/50v, x7r, 0603 1 c15 grm1885c1h150ja01d murata 15pf/50v, x7r, 0603 1 c1608c0g1h150f080aa tdk j1 ? j10 molex ( 11 ) header 2 10 r1 mct06030z0000zp500 vishay ( 12 ) beyschlag 0 ? 1 r2, r12, r13 ( open ) r3 crcw06031k91fkea vishay dale 1.91k, 1%, 1/10w,0603 1 r4 crcw06033k24fkea vishay dale 3.24k, 1%, 1/10w,0603 1 r5 crcw06034k75fkea vishay dale 4.75k, 1%, 1/10w,0603 1 r6 crcw06038k06fkea vishay dale 8.06k, 1%, 1/10 w,0603 1 r7 crcw060311k5fkea vishay dale 11.5k, 1%, 1/10w,0603 1 r8 crcw06020k0fkea vishay dale 20k, 1%, 1/10w,0603 1 r9 crcw060340k2fkea vishay dale 40.2k, 1%, 1/10w,0603 1 r10 crcw0603100k0fkea vishay dale 100k, 1%, 1/10w,0603 1 r11 , r16 crcw06 0349k9fkea vishay dale 49.9k, 1%, 1/10w,0603 2 r14 crcw060310k0fkea vishay dale 10k, 1%, 1/10w,0603 1 r15 crcw06031k 0 7fkea vishay dale 1. 0 7k, 1%, 1/10w,0603 1 tp1 ? tp16 molex header 1 16 u1 MIC45208 - 1 ym p micrel, inc . ( 13 ) 26v/10a, dc - to - dc power module 1 MIC45208 - 2 ym p notes: 11. molex: www.molex.com . 12. vishay - dale: www.vishay.com . 13. micrel, inc.: www.micrel.com .
micrel, inc. MIC45208 may 29 , 2014 30 revision 1. 2 package information ( 14 ) 52 - pin 10 mm 10 mm qfn ( mp ) note: 14. package information is correct as of the publication date. for updates and most current information, go to www.micrel.com .
micrel, inc. MIC45208 may 29 , 2014 31 revision 1. 2 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 responsib ility 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 d ocument. 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 warranties 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, devic es or systems 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 to 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 indemni fy micrel for any damages resulting from such use or sale. ? 20 14 micrel, incorporated.

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