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MIC45205 -1/ -2 26v/6 a dc - to - dc power module general description micrel?s MIC45205 is a synchronous step - down regulator module, featuring a unique adaptiv e on - time control architecture. the module incorporates a dc - to - dc controller, power mosfets, bootstrap diode, bootstrap capacitor , and an inducto r 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. t he fully - optimized design can deliver up to 6a current under a wide input voltage range of 4.5v to 26v, without requiring additional cooling. the MIC45205 - 1 uses micrel ?s hyperlight load ? (hll) MIC45205 - 2 uses micrel ?s hyper speed con trol ? architecture which enables ultra - fast load transient response , allowing for a reduction of output capacitance. the MIC45205 offers 1% output accuracy that can be adjusted from 0.8v to 5.5v with two external resistors. additional features include the rmal shutdown protection , input undervoltage lockout, adjustable current limit, and short circuit protection. the MIC45205 allows for safe start - up into a pre - biased output. datasheet and other support documentation can be found on micrel?s web site at: www.micrel.com . features ? no compensation required ? up to 6a 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 ope n - drain power good output ? hyper speed control (MIC45205 - 2) architecture enables fast transient response ? hyperlight load (MIC45205 - 1) improves light load efficiency ? supports safe startup into pre - biased output ? cispr22, class b compliant ? ? 40 c to +125 c jun ction temperature range ? thermal - shutdown protection ? short - circuit protection with hiccup mode ? adjustable current limit ? available in 52 - pin 8mm 8mm 3mm qfn package applications ? high power density point - of - load conversion ? servers, routers , networking , an d 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 1 2 3 4 5 6 7 8 9 efficiency (%) output current (a) efficiency (v in = 12v) vs. output current (MIC45205 - 1) f sw = 600khz 1.8v out 5.0v out 1.2v out 1.5v out 0.8v out 1.0v out 2.5v out 3.3v out 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 april 15, 2014 revisio n 1.0
micrel, inc. MIC45205 ordering information ( 1) part number switching f requency features junction temperature range package lead finish MIC45205 -1 ym p 2 00khz to 600khz hyper light load ? 40c to +125c 52- pin 8 mm 8 mm 3mm qfn pb - free MIC45205 - 2ym p 200khz to 600khz hyper speed control ? 40c to +125c 52- pin 8 mm 8 mm 3mm qfn pb - free note: 1. devices are esd s ensitive. handling precautions are recommended. pin configuration 52- pin 8mm 8mm 3mm qfn (top view) april 15, 2014 2 revision 1 .0
micrel, inc. MIC45205 pin description mic4520 5 pin number pin name pin function 1 gnd analog ground. connect bottom feedback resistor to gnd. gnd and pgnd should be connected together at a low impedance point. 2, 3 5vdd internal +5v linear regulator output . powered by vin, 5 vdd 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 linear regulator. 4, 5 pvdd pvdd. supply input for the internal low - side power mosfet driver. 6, 7 , 8, 45, 52 p gnd 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 capacitors . 9 - 12, 30 - 35 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 mosfet during off time. 1 3 -1 9 pvin power input voltage. connection to the drain of the i nternal high side power mosfet. connect a n input capacitor from p vin to pgnd. 20 - 29 vout output voltage. connected to the internal inductor, the output capacitor should be connected from this pin to pgnd as close to the module as possible. 36 - 38 ri a 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 connection of internal bootstrap diode, this pin should be connected to the p vdd pin. 4 2 - 44 bst connection to the intern al bootstrap circuitry and high - side power mosfet drive circuitry. leave floating, no connect ion . 46 fb feedback. input to the transconductance amplifier of the control loop. the fb pin is r eferenced to 0.8v. a resistor divider co nnecting 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 extern al bias voltage. 48 en enable. 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 shutdown . en pin has an internal 1m ? (typical) pull - down resistor to gnd. 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 prog ram the switching frequency. connect ing freq to vin sets frequency = 600khz. 51 ilim current limit. connect a resistor between ilim and sw to program the current limit. april 15, 2014 3 revision 1 .0
micrel, inc. MIC45205 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 freq , 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 g nd ................................ .............. ? 0.3v to +0.3v junction temperature ................................ .............. +150c storage temperature (t s ) ......................... ? 65 c to +150 c le ad temperature (soldering, 10s ) ............................ 260c operating ratings ( 3 ) supply voltage ( v pvin , v vin ) .............................. 4. 5 v to 26v output current ................................ ................................ . 6a ena ble 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) 8 mm 8 mm 3mm qfn - 52 ( ja ) ................ 2 1.7 c/w 8 mm 8 mm 3mm qfn - 52 ( jc ) .................. 5.0 c/w electrical characteristics ( 5) 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 suppl y input input voltage range ( v p v in , v in ) 4.5 2 6 v quiescent supply current (MIC45205 -1) v fb = 1.5v 0.35 0.75 ma quiescent supply current (MIC45205 -2) v fb = 1.5v 2.1 3 ma operating current v pvin = v in = 12v, v out = 1.8 v, i out = 0 a f sw = 600khz (mi c45205 -2) 31 ma shutdown supply current sw = unconnected, v en = 0v 0.1 10 a 5vdd output 5vdd output voltage v in = 7v to 26 v, 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 ld o 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 ? 40c ? t j ?? c 0.784 0.8 0.816 fb bias current v fb = 0.8v 5 500 na notes: 2. exceeding the absolute maximum rating may damage the device. 3. the device is not guaranteed to function outside operating range. 4. ja and jc were measured using the MIC45205 evaluati on board. 5. specification for packaged product only. april 15, 2014 4 revision 1 .0
micrel, inc. MIC45205 electrical characteristics ( 5) (continued) 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 other wise noted. parameter condition min . typ . max . units 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 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 = 1 v 0 % minimum off - time 140 200 260 ns soft - start soft - start time 5 ms short - circuit protection current - limit threshold v fb = 0.79v ? 30 ? 14 0 mv sho rt - circuit threshold v fb = 0v ? 23 ? 7 9 mv current - limit source current v fb = 0.79v 55 70 85 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 threshold vo ltage 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 overt emperature shutdown t j rising 160 c overt emperature shutdown hysteresis 1 5 c april 15, 2014 5 revision 1 .0
micrel, inc. MIC45205 typical characteristics 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 (MIC45205 - 1) v in = 12v v out = 1.8v i out = 0a f sw = 600khz 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 0.0 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 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 0.5 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 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 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 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 april 15, 2014 6 revision 1 .0
micrel, inc. MIC45205 typical characteristics (continued) 10 20 30 40 50 60 70 80 90 100 0 1 2 3 4 5 6 7 8 9 efficiency (%) output current (a) efficiency (v in = 5v) vs. output current (mic4205 - 1) f sw = 600khz 1.8v out 1.2v out 1.5v out 0.8v out 1.0v out 2.5v out 3.3v out 10 20 30 40 50 60 70 80 90 100 0 1 2 3 4 5 6 7 8 9 efficiency (%) output current (a) efficiency (v in = 12v) vs. output current (MIC45205 - 1) f sw = 600khz 1.8v out 5.0v out 1.2v out 1.5v out 0.8v out 1.0v out 2.5v out 3.3v out 10 20 30 40 50 60 70 80 90 100 0 1 2 3 4 5 6 7 8 9 efficiency (%) output current (a) efficiency (v in = 24v) vs. output current (MIC45205 - 1) f sw = 600khz 1.8v out 5.0v out 1.2v out 1.5v out 0.8v out 1.0v out 2.5v out 3.3v out 10 20 30 40 50 60 70 80 90 100 0 1 2 3 4 5 6 7 8 9 efficiency (%) output current (a) efficiency (v in = 5v) vs. output current (MIC45205 - 2) f sw = 600khz 1.8v out 1.2v out 1.5v out 0.8v out 1.0v out 2.5v out 3.3v out 10 20 30 40 50 60 70 80 90 100 0 1 2 3 4 5 6 7 8 9 efficiency (%) output current (a) efficiency (v in = 12v) vs. output current (MIC45205 - 2) f sw = 600khz 1.8v out 5.0v out 1.2v out 1.5v out 0.8v out 1.0v out 2.5v out 3.3v out 10 20 30 40 50 60 70 80 90 100 0 1 2 3 4 5 6 7 8 9 efficiency (%) output current (a) efficiency (v in = 24v) vs. output current (MIC45205 - 2) f sw = 600khz 1.8v out 5.0v out 1.2v out 1.5v out 0.8v out 1.0v out 2.5v out 3.3v out -1.0% -0.8% -0.6% -0.4% -0.2% 0.0% 0.2% 0.4% 0.6% 0.8% 1.0% 5.5 9.8 14.1 18.4 22.7 total regulation (%) input voltage (v) line regulation v out = 1.8v i out = 0a 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) output voltage vs. input voltage v out = 1.8v i out = 4a april 15, 2014 7 revision 1 .0
micrel, inc. MIC45205 typical characteristics (continued) 0 0.5 1 1.5 2 2.5 3 0 1 2 3 4 5 6 7 8 9 ic power dissipation (w) output current (a) ic power dissipation (v in = 5v) vs. output current v in = 5v f sw = 600khz 1.8v out 1.2v out 1.5v out 0.8v out 1.0v out 2.5v out 3.3v out 0 0.5 1 1.5 2 2.5 3 3.5 0 1 2 3 4 5 6 7 8 9 ic power dissipation (w) output current (a) ic power dissipation (v in = 12v) vs. output current v in = 12v f sw = 600khz 1.8v out 5.0v out 1.2v out 1.5v out 0.8v out 1.0v out 2.5v out 3.3v out 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 1 2 3 4 5 6 7 8 9 ic power dissipation (w) output current (a) ic power dissipation (vin = 24v) vs. output current vin = 12v f sw = 600khz 1.8v out 5.0v out 1.2v out 1.5v out 0.8v out 1.0v out 2.5v out 3.3v out april 15, 2014 8 revision 1 .0
micrel, inc. MIC45205 fun ctional characteristics april 15, 2014 9 revision 1 .0
micrel, inc. MIC45205 functional characteristics (continued) april 15, 2014 10 revision 1 .0
micrel, inc. MIC45205 functional characteristics (continued) april 15, 2014 11 revision 1 .0
micrel, inc. MIC45205 functional diagram april 15, 2014 12 revision 1 .0
micrel, inc. MIC45205 functional description the MIC45205 is an adaptive on - time s ynchronous buck regulator module built for high - input voltage to low - output voltage conversion applications. the MIC45205 is designed to operate over a wide input voltage range, from 4.5v to 26v, and the output is adjustable with an external resistor divid er. 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 implemented by sensing low - side mosfet?s r ds(on) . the device featur es internal soft - start, enable, uvlo, and thermal shutdown. the module has integrated switching fets, inductor, bootstrap diode, resistor , and capacitor. theory of operation as shown in figure 1 ( in association wit h equation 1 ), the output voltage is sensed by the MIC45205 feedback pin ( fb ) via the voltage divider r fb1 and r fb2 and compared to a 0.8v reference voltage ( v ref ) at the error comparator through a low - gain transconductance (gm) amplifier. if the feedback voltage decreases , and the amplifier output 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 sw in out ) estimated ( on f v v t = at the end of the on - time period, the internal high - side driver tur ns 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 - ti me 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 MIC45205 control logic will apply the t off(min) instead. t off(min) is requ ired 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 ) : s s ) min ( off s max t ns 200 1 t t t d ? = ? =
micrel, inc. MIC45205 figure 2 . MIC45205 control loop timing figure 3 shows the operation of the mic 45205 during a load transient. the output voltage drops due to the sudden load increase, 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 voltage 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 ret urns to the nominal fixed frequency once the output has stabilized at the new 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 s witching 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 relativel y limited during load transient , t on stays virtually close to its steady - state val ue. figure 3 . MIC45205 load transient response unlike true current - mode control, the mi c45205 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 stability requirements, the MIC45205 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 c omparator. the recommended feedback voltage ripple is 20mv~100mv over full input 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, th e 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 the application information section for more details about the ripple injection technique. discontinuous mode ( MIC45205 - 1 only) in continuou s mode , the inductor current is always greater than zero; however, at light loads , the MIC45205 - 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 this 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 MIC45205 - 1 wakes up and turns on the high - side mosfet when the feedback voltage v fb drop s below 0.8v. the MIC45205 - 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 MIC45205 - 1 automatically powers down most of the ic circuitry and goes into a low - power mode. once the MIC45205 - 1 goes into discontinuous mode, both dl and dh are low, which turns off the h igh - side and low - side mosfets. the load current is supplied by the output capacitors 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. april 15, 2014 14 revision 1 .0
micrel, inc. MIC45205 figure 4 . mic 45205 - 1 control loop timing (discontinuous mode) during discontinuous mode, the bias current of most circuits is substantially reduced. as a result, the total power suppl y current during discontinuous mode is only about 350 a , allowing the MIC45205 - 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 tim e. the input surge appears while the output capacitor is charged up. the MIC45205 implements an internal digital soft - start by making the 0.8v reference voltage v ref ramp from 0 to 100% in about 5 ms with 9.7mv steps . therefore, the output voltage is contr olled 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 lim it the MIC45205 uses the r ds(on) of the low - side mosfet and external resistor connected from ilim pin to sw node to set the current limit. figure 5 . MIC45205 current - limiting circuit in each switching cycle of the MIC45205, the inductor current is sensed by monitoring the low - side mosfet in the off period. 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 capacitor (c15) connected from ilim pin to pgnd filters the switching node ringing during the o ff - time allowing a better short - limit measurement. the time constant created by r15 and c 6 should be much less than the minimum off time. the v cl drop allows programming 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 , a n over current is triggered causing the ic to enter hiccup mode . the hiccup sequence 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 progr ammed by using equation 3. ( ) + ? ? = . v cl = current - limit threshold (typical absolute value is 14mv per the electrical characteristics table ). i cl = current - limit source current (typical value is 70 a, per the electrical characteristics table). april 15, 2014 15 revision 1 .0
micrel, inc. MIC45205 i l(pp) = inductor current peak - to - peak, sinc e the inductor is integrated use equation 4 to calculate the inductor ripple current. the peak - to - peak inductor current ripple is: l f v ) v (v v i sw in(max) out in(max) out l(pp) u u u ' eq. 4 the MIC45205 has a 1.0h inductor integrated into the module. in case of a hard short, the sho rt limit is folded down to allow an indefinite hard short on the output without any destructive effect. it is mandatory to make sure that the inductor current used to charge the ou tput capacitance during soft - start is under the folded short limit; otherwis e the supply will go in hiccup mode and may not finish the soft - start successfully. 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 incre ased mosfet junction temperature rise. with r15 = 1.37k ? and c15 = 15pf, the typical output current limit is 8a. april 15, 2014 1 6 revision 1 .0
micrel, inc. MIC45205 application information setting the switching frequency the MIC45205 switching frequency can be adjusted by changing the value of resistors r1 and r2. figure 6 . sw itching frequency adjustment equation 5 gives the estimated switching frequency: 2 r 1 r 2 r f f o sw + = electrical characteristics (5) table ) r1= n lvuhfrpphqghg r2 n eeds 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 conditions as MIC45205 uses and adaptive on - time architect ure as explained in the ? theory of operation ? subsection in the functional description . 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 capacitor. recommended capacitor types are mlcc, os - con and poscap. the output capacitor?s esr is usu ally the main cause of the output ripple. the MIC45205 requires ripple injection and the output capacitor esr affects the control loop from a stability point of view. the maximum value of esr is calculated as in equation 6: l(pp) out(pp) out c ?, ?9 esr out(pp) = peak - to - peak output voltage ripple ?, l(pp) = peak - to - peak inductor current ripple 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 v in = 12v r1 = 100k april 15, 2014 17 revision 1 .0
micrel, inc. MIC45205 the total output ripple is a combination of the esr and output capacitance. the total ripple is calculated in equation 7: ( ) 8 f c ?, ?9 + ? ? ? ? ? ? ? ? = functional description , the MIC45205 requires at least 20mv peak - to - peak ripple at the fb pin to make the gm 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 output 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 enoug h feedback voltage ripple. please refer to ? ripple injection ? subsection in the application information section for more details. the output capacitor rms current is calcul ated in equation 8: 12 ?, i l(pp) (rms) c out = = input capacitor selection the input capacitor for the power stage input pvin should be selected for ripple curr ent rating a nd voltage rating. the input voltage ripple will primarily depend on the input capacitor?s esr. the peak input current is equal to the peak inductor current, so: in c ) pk ( l in esr i v = ? ? = ? april 15, 2014 18 revision 1 .0
micrel, inc. MIC45205 output voltage setting components the MIC45205 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: ? ? ? ? ? ? ? ? + = 2 fb 1 fb fb out r r 1 v v eq. 14 where: v fb = 0.8v a typical value of r fb1 used on the standard evaluation erduglvn ,i5lvwrrodujhlwpd\doorzqrlvhwreh introduced into the voltage feedback loop. if r fb1 is too small in value, it will decrease the efficiency of the power supply, especially at light loads. once r fb1 is selected, r fb2 can be calculated using equation 15: fb out fb1 fb fb2 v v r v r ? = =??? r fb2 . table 1 provides r fb2 values for some common output voltages. table 1 . v out pro gramming resistor look -up r fb 2 v out open 0.8v 40.2 k? 1.0v 20k? 1.2v 11.5 k? 1.5v 8.0 6 k? 1.8v 4.75 k? 2.5v 3.24 k? 3.3v 1.91 k? 5.0v ripple injection the v fb ripple required for proper operation of the mi c45205 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 volta ge ripple is so small that the g m amplifier and error comparator cannot sense it, then the MIC45205 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 output v oltage 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 april 15, 2014 19 revision 1 .0
micrel, inc. MIC45205 the feedback voltage ripple is: l(pp) out c fb2 fb1 fb2 fb(pp) i esr r r r v = i l(pp) = the peak - to - peak value of the inductor current ripple 2. virtually 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. MIC45205 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 injected rip ple is: w u u u u u sw div in fb(pp) f 1 d) - (1 d k v v = t = (r fb1 //r fb2 //r inj ) u c14 r inj = 10 k ? c inj = 0.1 f in equations 18 and 19, it is assumed that the ti me constant associated with c14 must be much greater than the switching period: 1 t f 1 sw w w u eq. 19 if the voltage divider resistors r fb1 and r fb2 are in the k range, then a c14 of 1nf to 100nf can easily satisfy the large time constant requi rements. april 15, 2014 20 revision 1 .0
micrel, inc. MIC45205 thermal measurements and safe operating area (soa) measuring the ic?s 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 results. the mos t 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 measurement 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 b e 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, an 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 measuring 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 MIC45205 is shown in figure 11 , figure 12 , figure 13 , figure 14 , and figure 15 . these thermal measurements were taken on MIC45205 evaluation board. since the MIC45205 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 MIC45205. soa curves should only be used as a point of reference. soa data was acquired using the MIC45205 e valuation board. thermal performance depends on the pcb layout, board size, copper thickness, number of thermal vias, and actual airflow. april 15, 2014 21 revision 1 .0
micrel, inc. MIC45205 figure 11. MIC45205 power derating vs. airflow (5v in to 1.5v out ) figure 12. MIC45205 power derating vs. airflow (12v in to 1.5v out ) figure 13. MIC45205 power derating vs. airflow (12v in to 3.3 v out ) figure 14. MIC45205 power derating vs. airflow (24v in to 1.5v out ) figure 15. MIC45205 power derating vs. airflow (24v in to 3.3v out ) 3 4 5 6 7 85 90 95 100 105 110 115 120 125 maximum output current (a) ambient temperature( 0 lfm 200 lfm 400 lfm 3 4 5 6 7 80 85 90 95 100 105 110 115 120 maximum output current (a) ambient temperature ( 0 lfm 200 lfm 400 lfm 3 4 5 6 7 80 85 90 95 100 105 110 115 120 maximum output current (a) ambient temperature ( 0 lfm 200 lfm 400 lfm 3 4 5 6 7 70 75 80 85 90 95 100 105 110 115 120 maximum output current (a) ambient temperature ( 0 lfm 200 lfm 400 lfm 3 4 5 6 7 60 65 70 75 80 85 90 95 100 105 110 maximum output current (a) ambient temperature ( 0 lfm 200 lfm 400 lfm april 15, 2014 22 revision 1 .0
micrel, inc. MIC45205 pcb layout guidelines warning: to minimize emi and outp ut noise, follow these layout recommendations. pcb l ayout is critical to achieve reliable, stable and efficient performance. 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 layer 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 mic 45205 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 only one location with a low impedance . input capacitor ? place the input capacitors on the same side of the board and as close to the ic a s possible. ? place several vias to the ground plane close to the input capacitor ground terminal. ? use either x7r or x5r dielectric input capacitors. do not use y5v or z5u type capacitors. ? do not replace the ceramic input capacitor with any other type of cap acitor. 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 electrolytic bypass capacitor must be used to limit the over - voltage spike seen on the input 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 es r changes. ? the feedback trace should be separate from the power trace and connected as close as possible to the output capacitor. sensing a long high - current load trace can degrade the dc load regulation. april 15, 2014 23 revision 1 .0
micrel, inc. MIC45205 pcb layout recommendations top ? copper layer 2 april 15, 2014 24 revision 1 .0
micrel, inc. MIC45205 pcb layout recommendations (continued) copper layer 3 bottom ? april 15, 2014 25 revision 1 .0
micrel, inc. MIC45205 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 = 8.00mm + (0.20 mm per side 2 sides) = 8.40 mm after completion of the periphery pad design, the larger exposed pads will be designed to create the mounting surface of the qfn exposed heatsink. 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 recommended. the typical via hole diameter is 0.30 mm to 0.35mm, with center - to - center pitch of 0.80 mm to 1.20 mm. note: exposed metal t race is ?mirror image? of package bottom view . figure 17. package bottom view vs. pcb recommended exposed metal trace april 15, 2014 26 revision 1 .0
micrel, inc. MIC45205 solder paste stencil design (recommend stencil thickness = 112.5 12.5 m) the solder stencil aperture opening s should be smaller than the periphery or large pcb exposed pads to reduce any chance of build - up of excess solder at the large exposed 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. 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 expose d trace keep out area . figure 18. solder stencil opening figure 19. stack - up of pad layout and solder paste stencil april 15, 2014 27 revision 1 .0
micrel, inc. MIC45205 evaluation board schematic bill of materials item part number manufacturer desc ription qty . bj1, bj2 571- 0500 (red) deltron ( 6 ) con, pcb mount - insulated socket 2 bj3, bj4 571- 0100 (black) deltron con, pcb mount - insulated socket 2 c1 b41851 epcos ( 7 ) 220 f/35v, ale cap acitor (optional) 1 c2 grm32er71h475ka12 murata ( 8 ) 4.7f/50v, x7r,1210, ceramic cap acitor 1 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 . april 15, 2014 28 revision 1 .0
micrel, inc. MIC45205 bill of materials (continued) item part number manufacturer description qty . c5 12106d107mat2a avx 100 f/6.3v, x5r, 1210, ceramic cap acitor 1 grm32er60j107me20l murata c3225x5r0j107m tdk c7, c 13 ( open ) 2 c14 c1608c0g1h222jt tdk 2.2nf/50v, x7r, 0603 1 c15 grm1885c1h150ja01d mur ata 15pf/50v, x7r, 0603 1 c1608c0g1h150f080aa tdk j1 ? j10 90120 - 0122 molex ( 11) header 2 10 r1 0 ? resistor 1 r2, r12, r13 ( open ) 3 r3 crcw06031k91fkea vishay dale ( 12) 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 r6 crcw06038k06fkea vishay dale 8.06k 1%, 1/10w, 0603 1 r7 crcw060311k5fkea vishay dale 1 1.5 k : 1 r8 crcw06020k0fkea vishay dale 20k , 1%, 1/10w, 0603 1 r9 crcw060340k2fkea vishay dale 40.2 k , 1%, 1/10w, 0603 1 r10 crcw0603100k0fkea vishay dale 100k , 1%, 1/10w, 0603 1 r11 crcw060349k9fkea vishay dale 49.9 k :3 1 r14 crcw060310k0fkea vishay dale 10k , 1%, 1/10w, 0603 1 r15 crcw06031k37fkea vishay dale 1.37 k : 1 r16 crcw060349r9fkea vishay dale 49.9 ? 1%, 1/10w, 0603 1 tp1 ? tp16 molex header 1 16 u1 MIC45205 -1 ym p MIC45205 -2 ym p micrel, inc . ( 13) 26v/6a dc -to - dc power module 1 note s : 11. molex: www.molex.com . 12. vishay - dale: www.vishay.com . 13. micrel, inc.: www.micrel.com . april 15, 2014 29 revision 1 .0
micrel, inc. MIC45205 package information ( 14) 52- pin 8mm 8mm qfn (mp) note: 14. package information is correct as of the publication date. for updates and most current information, go to www.micrel.com . april 15, 2014 30 revision 1 .0
micrel, inc. MIC45205 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, arisi ng by estoppel or otherwise, to any intellectual property rights is granted by this document. except as provided in micrel?s terms and conditions of sale for such products, micrel assumes no liability whatsoever, and micrel disclaims any express or implie d 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, devices or systems where mal function of a product can reasonably be expected to result in personal injury. life support devices or systems are devices or syste ms 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 purchaser?s use or sale of micrel products for use in life support appliances, devices or systems is a purchaser?s own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2014 micrel, incorporated. april 15, 2014 31 revision 1 .0

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