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mic 23450 3mhz, pwm, 2a triple buck regulator with hyperlight load ? and power good hyperlight load is a registered trademark of micrel, inc mlf and micro leadframe are registered trademark s of amkor technology , inc. micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel +1 (4 08) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com december 2012 m9999 -1207 12 -a general description the MIC23450 is a high - efficiency, 3 mhz, triple 2a , synchronous buck regulator with hyperlight load ? mode. hyperlight load provides very - high efficiency at light loads and ultra - fast transient response which is perfectly suited for s upply ing processor core voltages. an additional benefit of this proprietary architecture is very low output ripple voltage throughout the entire load range with the use of small output capacitors. the 5mm x 5mm mlf ? package saves board space and requires o nly five external components for each channel. the MIC23450 is designed for use with a very small inductor, down to 0.4 7 h, and an output capacitor as small as 2.2f that enables a total solution size, less than 1mm height. the MIC23450 has a very - low quie scent current of 23a each channel and achieves as high as 81% efficiency at 1ma. at higher loads, the MIC23450 provides a constant switching frequency around 3mhz while achieving peak efficiencies up to 93%. the MIC23450 is available in 32 - pin 5mm x 5mm m lf package with an operating junction temperature range from ? 40 c to +125 c. data sheets and support documentation can be found on micrel?s web site at : www.micrel.com . features ? input voltage: 2.7v to 5.5v ? 3 indepe ndent 2a outputs ? up to 93% peak efficiency ? 81% typical efficiency at 1ma ? three independent power good indicators ? 23 a typical quiescent current (per channel) ? 3mhz pwm operation in continuous mode ? ultra - f ast transient response ? low voltage output ripple ? 30mvpp ripple in hyperlight load mode ? 5mv output voltage ripple in full pwm mode ? fully integrated mosfet switches ? 0.01 a shutdown current (per channel) ? thermal - shutdown and current - limit protection ? output v oltage as low as 1 v ? 32- pin 5mm x 5mm mlf ? ? 40 c to +125 c junction temperature range applications ? portable navigation devices (gps) ? wifi/wimax/wibro modules ? digital cameras ? wireless lan cards ? portable applications ____________________________________________________________________________ ___________ _____ _____________________________ typical application
micrel, inc. MIC23450 december 2012 2 m9999 -1207 12 -a ordering information part number marking nominal output voltage junction temperature range (1) package (2, 3) lead finish MIC23450 - aaayml aaa adj/adj/adj ? 40c to +125 c 32- pin 5mm 5mm mlf pb - fre e note s : 1. other options available. contact micrel for details. 2. mlf is a green, rohs - compliant package. lead finish is nipdau. mold compound is halogen free. 3. mlf ? = pin 1 identifier . pin configuration 32- pin 5mm 5mm mlf (ml) ? adjustable top view pin description pin number pin name pin function 26, 23, 21 sw1, 2, 3 switch (output). internal power mosfet output switches for output 1/2/3. 30, 3, 8 en1, 2, 3 enable (input). logic high enables operation of regulator 1/2/3. logic low will shut down t he device. do not leave floating. 31, 4, 9 sns1, 2, 3 sense. connect to v out1,2,3 as close to output capacitor as possible to sense output voltage. 32, 5, 10 fb1, 2, 3 feedback. connect a resistor divider from output 1/2/3 to ground to set the output vol tage. 1, 6 , 1 2 pg1, 2, 3 power good. open drain output for the power good indicator for output 1/2/3. place a resistor between this pin and a voltage source to detect a power good condition. 2, 7, 11 agnd1, 2, 3 analog ground. connect to quiet ground poi nt away from high - current paths , e.g., c out for best operation. must be connected externally to pgnd. 27, 29, 14 pvin1, 2, 3 power input voltage. connect a capacitor to pgnd to localize loop currents and decouple switching noise. 28, 15, 13 avin1, 2, 3 a nalog input voltage. connect a capacitor to agnd to decouple noise. 24, 22, 18 pgnd1, 2, 3 power ground. 16, 17, 19, 20, 25 nc no connect . ep ad epad connect to ground plane to ensure good thermal properties.
micrel, inc. MIC23450 december 2012 3 m9999 -1207 12 -a absolute maximum ratings (1) supply voltage ( p v in, av in ) .................................. ? 0.3 to 6v sense (v sns1 , v sns2 , v sns3 ) . ................................. ? 0.3 to 6v power good (pg1, pg2, pg3) ............................ ? 0.3 to 6v output switch voltage (v sw1 , v sw2 , v sw3 ) ......... ? 0.3v to 6v enable input voltage (v en1 , v en2 , v en3 ) ............ ? 0.3v to v in storage temperature range .................... ? 65c to + 150 c e s d r ating (3) ................................................. esd sensitive operating ratings (2) supply v oltage (v in ) ..................................... + 2.7 v to + 5.5 v enable input voltage (v en1 , v en2 , v en3 ) ................. 0v to v in output voltage range (v sns1 , v sns2 , v sns3 ) ... + 1v to + 3.3v junction voltage range (t j ) ............... ? 40 c t j + 125 c thermal resistance 3 2 - pin 5mm 5mm mlf ( ja ) ......................... + 30 c/w 32- pin 5mm 5mm mlf ( jc ) ......................... + 10 c/w electrical characteristics (4) t a = + 25 c; v in = v en1 , v en2 , v en3 = 3 .6v; l 1 = l2 = l3 = 1 h ; c out1 , c out2 , c out3 = 4.7 f, unless otherwise specified. b old values indicate ? 40c t j + 125 c, unless noted. parameter condition min . typ . max . units supply voltage range 2.7 5.5 v undervoltage lockout threshold turn - on 2.45 2.55 2.65 v undervoltage lockout hysteresis 75 mv quiescent current i out = 0ma, sns > 1.2 v outnom 69 120 a per channel shutdown current v en1 , v en2 , v en3 = 0v; v in = 5.5v 0.01 5 a output voltage accuracy v in = 3.6v if v out(nom) < 2.5v, i load = 20ma ? 2.5 + 2.5 % v in = 4.5v if v out(nom) 2.5v, i load = 20ma feedback voltage (v fb1 , v fb2 , v fb3 ) .60 4 0.62 .635 v peak current limit i out1 , i out2 , i out3 sns1, sns2, sns3 = 0.9 v out nom 2 4.5 a foldback current limit 1.8 a output voltage line regulation (v out1 , v out2 , v out3 ) v in = 3.6v to 5.5v if v outnom1, 2, 3 < 2.5v, i load = 20ma 0.3 %/v v i n = 4.5v to 5.5v if v outnom1, 2, 3 2.5v, i load = 20ma output voltage load regulation (v out1 , v out2 , v out3 ) dcm: 20ma < i load < 130ma, v in = 3.6v if v outnom < 2.5v 0.2 % dcm: 20ma < i load < 130ma, v in = 5.0v if v outnom > 2.5v 0.4 ccm: 200ma < i load < 500ma, v in = 3.6v if v outnom < 2.5v 0.6 ccm: 200ma < i load < 1a, v in = 5.0v if v outnom > 2.5v 0.3 pwm switch on - resistance (r sw1 , r sw2 , r sw3 ) i sw1 , i sw2 , i sw3 = + 100ma (pmos) 0.2 ? i sw1 , i sw2 , i sw3 = ? 100ma (nmos) notes: 1. excee ding the absolute maximum rating may damage the device. 2. the device is not guaranteed to function outside its operating rating. 3. devices are esd sensitive. handling precautions recommended. human body model, 1.5k ? in series with 100pf. 4. specification for pack aged product only.
micrel, inc. MIC23450 december 2012 4 m9999 -1207 12 -a electrical characteristics (4) (continued) t a = + 25 c; v in = v en1 , v en2 , v en3 = 3 .6v; l 1 = l2 = l3 = 1 h ; c out1 , c out2 , c out3 = 4.7 f, unless otherwise specified. b old values indicate ? 40c t j + 125 c, unless noted. parameter condit ion min. typ. max. units maximum frequency i out1 , i out2 , i out3 = 120ma 3 mhz soft - start time v out1 , v out2 , v out3 = 90% 115 s power good threshold % of v nom 83 90 96 % power good hysteresis 10 % power good pull down v sns = 90% v nom , i pg = 1ma 200 mv enable threshold turn - on 0.5 0.8 1.2 v enable input current 0.1 1 a overtemperature shutdown 160 c overtemperature shutdown hysteresis 20 c
micrel, inc. MIC23450 december 2012 5 m9999 -1207 12 -a typical characteristics 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.001 0.01 0.1 1 10 efficiency (%) output current (a) efficiency vs. output current v out = 1.8v v in = 3v v in = 3.6v v in = 5v 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.001 0.01 0.1 1 10 efficiency (%) output current (a) efficiency vs. output current v out = 2.5v v in = 3v v in = 3.6v v in = 5v 0 1 2 3 4 5 6 7 8 2 3 4 5 6 current limit (a) input voltage (v) current limit vs. input voltage ch3 = 1.2v ch2 = 1.8v ch1 = 2.5v 0 20 40 60 80 100 120 140 160 180 2 3 4 5 6 supply current (na) input voltage (v) shutdown current vs. input voltage 1.7 1.75 1.8 1.85 1.9 2 2.5 3 3.5 4 4.5 5 5.5 6 output voltage (v) input voltage (v) line regulation (low loads) i out = 1ma i out = 20ma i out = 120ma 1.65 1.7 1.75 1.8 1.85 1.9 2 2.5 3 3.5 4 4.5 5 5.5 6 output voltage (v) input voltage (v) line regulation (high loads) i out = 1a i out = 2a 1.7 1.72 1.74 1.76 1.78 1.8 1.82 1.84 1.86 1.88 1.9 0 0.03 0.06 0.09 0.12 0.15 0.18 output voltage (v) load current (a) output voltage vs. output current (hll) v out = 1.8v v in = 3v v in = 3.6v v in = 5v 1.7 1.72 1.74 1.76 1.78 1.8 1.82 1.84 1.86 1.88 1.9 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 output voltage (v) load current (a) output voltage vs. output current (ccm) v out = 1.8v v in = 3v v in = 5v v in = 3.6v 1.74 1.76 1.78 1.80 1.82 1.84 -60 -40 -20 0 20 40 60 80 100 120 140 output voltage (v) temperature ( c) output voltage vs. temperature v in = 5.5v v in = 3.6v v in = 2.7v
micrel, inc. MIC23450 december 2012 6 m9999 -1207 12 -a typical characteristics (contin ued) 0 20 40 60 80 100 2 3 4 5 6 pg delay (s) input voltage (v) pg delay time vs. input voltage pg rising pg falling 0.83 0.84 0.85 0.86 0.87 0.88 0.89 0.9 0.91 2 2.5 3 3.5 4 4.5 5 5.5 6 pg threshold (% of vref) input voltage (v) pg thresholds vs. input voltage pg rising pg falling 2.47 2.49 2.51 2.53 2.55 2.57 -60 -40 -20 0 20 40 60 80 100 120 140 uvlo threshold (v) temperature ( c) uvlo threshold vs. temperature uvlo rising uvlo falling 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 2 2.5 3 3.5 4 4.5 5 5.5 6 enable threshold (v) input voltage (v) enable threshold vs. input voltage t amb = 25 c 0.5 0.6 0.7 0.8 0.9 1 1.1 -60 -40 -20 0 20 40 60 80 100 120 140 enable threshold (v) temperature ( c) enable threshold vs. temperature v in = 5.5v v in = 3.6v v in = 2.7v 0.1 1 10 100 1000 10000 0.0001 0.001 0.01 0.1 1 10 frequency (khz) output current (a) switching frequency vs. load current v out = 1.8v v in = 5v v in = 3v v in = 3.6v 0.600 0.605 0.610 0.615 0.620 0.625 0.630 0.635 0.640 -60 -40 -20 0 20 40 60 80 100 120 140 vfb (v) temperature ( c) vfb vs. temperature v in = 2.7v v in = 5.5v v in = 3.6v 0.0 0.5 1.0 1.5 2.0 2.5 20 40 60 80 100 120 140 current per output (a) ambient temperature ( c) maximum output current per o/p vs. temperature (1 o/p) v in = 3.6v v out = 1v v out = 2.8v 0.0 0.5 1.0 1.5 2.0 2.5 20 40 60 80 100 120 140 current per output (a) ambient temperature ( c) maximum output current per o/p vs. temperature (2 o/ps) v in = 3.6v v out = 1v v out = 2.8v
micrel, inc. MIC23450 december 2012 7 m9999 -1207 12 -a typical characteristics (continued) 0.0 0.5 1.0 1.5 2.0 2.5 20 40 60 80 100 120 140 max output current (a) ambient temperature ( c) maximum output current per o/p vs. temperature (3 o/ps) v in = 3.6v v out = 1v v out = 2.8v 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 0 0.5 1 1.5 2 2.5 power dissipation (w) output current (a) power dissipation vs. load current (per channel) vout = 1.8v vout = 2.5v 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 0 20 40 60 80 100 120 140 power dissipation (w) ambient temperature ( c) maximum package dissipation vs. ambient temperature
micrel, inc. MIC23450 december 2012 8 m9999 -1207 12 -a functional characteristics
micrel, inc. MIC23450 december 2012 9 m9999 -1207 12 -a functional characteristics (continued)
micrel, inc. MIC23450 december 2012 10 m9999 -1207 12 -a functional characteristics (continued)
micrel, inc. MIC23450 december 2012 11 m9999 -1207 12 -a functional diagram figure 1. simplified MIC23450 adjustable functional block diagram
micrel, inc. MIC23450 december 2012 12 m9999 -1207 12 -a functional description pvin the input supply (pvin) provides power to the internal mosfets for the switch mode regulator. the vin operating r ange is 2.7v to 5.5v so an input capacitor, with a minimum voltage rating of 6.3v, is recommended. due to the high di/dt switching speeds, a minimum 2.2f or 4.7 f recommended bypass capacitor placed close to pvin and the power ground (pgnd) pin is require d. refer to the layout recommendations for details. avin the input supply (avin) provides power to the internal control circuitry. as the high di/dt switching speeds on pvin cause small voltage spi kes, an rc filter comprising 50? and a minimum 100nf decoup ling capacitor placed close to the avin and signal ground (agnd) pin is required. en a logic high signal on the enable pin activates the output voltage of the device. a logic low signal on the enable pin deactivates the output and reduces supply current to 0.01a. MIC23450 features internal soft - start circuitry that reduces in - rush current and prevents the output vol t age from overshooting at start up. do not leave the en pin floating. sw the switch (sw) connects directly to one end of the inductor and provi des the current path during switching cycles. the other end of the inductor is connected to the load, sns pin and output capacitor. due to the high speed switching on this pin, the switch node should be routed away from sensitive nodes. sns the sense (sns) pin is connected to the output of the device to provide feedback to the control circuitry. the sns connection should be placed close to the output capacitor. refer to the layout recommendations for more details. agnd the analog ground (agnd) is the ground path for the biasing and control circuitry. the current loop for the signal ground should be separate from the power ground (pgnd) loop. refer to the layout recommendations for more details. pgnd the power ground pin is the ground path for the high curren t in pwm mode. the current loop for the power ground should be as short and wide as possible and separate from the analog ground (agnd) loop as applicable. refer to the layout recommendations for more details. pg the power good (pg) pin is an open drain ou tput which indicates logic high when the output voltage is typically above 90% of its steady state voltage. a pull - up resistor of more than 5k ? should be connected from pg to v out . fb the feedback (fb) pin is the control input for programming the output vo ltage. a resistor divider network is connected to this pin from the output and is compared to the internal 0.62v reference within the regulation loop. the output voltage can be programmed between 1v and 3.3v using equation 1 : ? ? ? ? ? ? + ? = r2 r1 1 v v ref out eq. 1 where: r1 is the top, v out connected resistor, r2 is the bottom, agnd connected resistor. table 1 illustrates e xample feedback resistor values . v out r1 r2 1.2v 274k 294k 1.5v 316k 221k 1.8v 301k 158k 2.5v 324k 107k 3.3v 309k 71.5k table 1. feed back resistor values
micrel, inc. MIC23450 december 2012 13 m9999 -1207 12 -a application information the MIC23450 is a triple high performance dc - to - dc step down regulator offering a small solution size. supporting 3 outputs with currents up to 2a inside a 5 mm x 5 mm mlf package, the ic requires only five external components per channel while meeting today?s miniature portable electronic device n eeds. using the hyperlight load switching scheme, the MIC23450 is able to maintain high efficiency throughout the entire load range while providing ultra - fast load transient response. the following sections provide additional device application information. input capacitor a 2.2f ceramic capacitor or greater should be placed close to the pvin pin for each channel and it?s corresponding pgnd pin for bypassing. for example, murata grm188r60j475me19d, size 0603, 4.7f ceramic capacitor is ideal, based upon performance, size and cost. a x5r or x7r temperature rating is recommended for the input capacitor. y5v temperature rating capacitors, aside from losing most of their capacitance over temperature, can also become resistive at high frequencies. this reduces their ability to filter out high frequency noise. output capacitor the MIC23450 is designed for use with a 2.2f or greater ceramic output capacitor. increasin g the output capacitance will lower output ripple and improve load transient response but could also increase solution size or cost. a low equivalent series resistance (esr) ceramic output capacitor such as the murata grm188r60j475me84d, size 0603, 4.7f c eramic capacitor is recommended based upon performance, size and cost. both the x7r or x5r temperature rating capacitors are recommended. the y5v and z5u temperature rating capacitors are not recommended due to their wide variation in capacitance over temp erature and increased resistance at high frequencies. inductor selection when selecting an inductor, it is important to consider the following factors (not necessarily in the order of importance): ? inductance ? rated current value ? size requirements ? dc resista nce (dcr) the MIC23450 is designed for use with a 0.47h to 2.2h inductor. for faster transient response, a 0.47h inductor will yield the best result. on the other hand, a 2.2h inductor will yield lower output voltage ripple. for the best compromise o f these, generally, a 1 h is recommended. maximum current ratings of the inductor are generally given in two methods; permissible dc current and saturation current. permissible dc current can be rated either for a 40 c temperature rise or a 10% to 20% loss in inductance. ensure the inductor selected can handle the maximum operating current. when saturation current is specified, make sure that there is enough margin so that the peak current does not cause the inductor to saturate. peak current can be calcula ted as shown in equation 2 : ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + = l f 2 /v v 1 v i i in out out out peak eq. 2 as shown in equation 2 , the peak inductor current is inversely proportional to the switching frequency and the inductance; the lower the switching frequency or the inductance the higher the peak c urrent. as input voltage increases, the peak current also increases. the size of the inductor depends on the requirements of the application. refer to the typical application circuit and bill of materials for details. dc resistance (dcr) is also important . while dcr is inversely proportional to size, dcr can represent a significant efficiency loss. refer to the efficiency considerations. the transition between high loads (ccm) to hyper l ight l oad (hll) mode is determined by the inductor rippl e current and t he load current as illustrated in figure 2. figure 2. transition between ccm mode and hll mode
micrel, inc. MIC23450 december 2012 14 m9999 -1207 12 -a the diagram shows the signals for high side switch drive (hsd) for t on control, the inductor current and the low side switch drive (lsd) for t off control. in hll mode, the indu ctor is charged with a fixed t on pulse on the high side switch (hsd). after this, the lsd is switched on and current falls at a rate v out /l. the controller remains in hll mode while the inductor falling current is detected to cross app roximately - 50ma. when the lsd (or t off ) time reaches its minimum and the inductor falling current is no longer able to reach this - 50ma threshold, the part is in ccm mode and switching at a virtually constant frequency. once in ccm mode, the t off time wil l not vary. therefore, it is important to note that if l is large enough, the hll transition level will not be triggered. that inductor is: 50ma 2 135ns v l out max = eq. 3 compensation the MIC23450 is designed to be stable with a 0.47h to 2.2h inductor w ith a 4.7f ceramic (x5r) output capacitor. duty cycle the typical maximum duty cycle of the MIC23450 is 80%. efficiency considerations efficiency is defined as the amount of useful output power, divided by the amount of power supplied. 100 i v i v % efficiency in in out out ? ? ? ? ? ? ? ? = eq. 4 maintaining high efficiency serves two purposes. it reduces power dissipation in the power supply, reducing the need for heat sinks and thermal design considerations and it reduces consumption of current for battery - powered applications. redu ced current draw from a battery increases the devices operating time and is critical in hand held devices. there are two types of losses in switching converters; dc losses and switching losses. dc losses are simply the power dissipation of i 2 r. power is dissipated in the high side switch during the on cycle. power loss is equal to the high side mosfet r dson multiplied by the switch current squared. during the off cycle, the low side n - channel mosfet conducts, also dissipating power. device operating curre nt also reduces efficiency. the product of the quiescent (operating) current and the supply voltage represents another dc loss. the current required driving the gates on and off at a constant 4mhz frequency and the switching transitions make up the switchi ng losses. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.001 0.01 0.1 1 10 efficiency (%) output current (a) efficiency vs. output current v out = 1.8v v in = 3v v in = 3.6v v in = 5v figure 3. efficiency under load the figure above shows an efficiency curve. from no load to 100ma, efficiency losses are dominated by quiescent current losses, gate drive and transition losse s. by using the hyperlight load mode, the mic234 50 is able to maintain high efficiency at low output currents. over 100ma, efficiency loss is dominated by mosfet r dson and inductor losses. higher input supply voltages will increase the gate - to - source voltage on the internal mosfets, thereby reducing the internal r dson . this improves efficiency by reducing dc losses in the device. all but the inductor losses are inherent to the device. in which case, inductor selection becomes increasingly critical in efficiency calculations. as the inductors are reduced in size, the dc resistance (dcr) can become quite significant. the dcr losses can be calculated as follows: p dcr = i out 2 x dcr eq. 5
micrel, inc. MIC23450 december 2012 15 m9999 -1207 12 -a from that, the loss in efficiency due to inductor resistance can be calculated as follows: 100 p i v i v 1 loss efficiency dcr out out out out ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + ? = eq . 6 efficiency loss due to dcr is minimal at light loads and gains significance as the load is increased. inductor selection becomes a trade - off between efficiency and size in this case. thermal considerations as most applications will not require 2a cont inuous current from all outputs at all times, it is useful to know what the thermal limits will be for various loading profiles. the allowable overall package dissipation is limited by the intrinsic thermal resistance of the package (r (j -c) ) and the area of copper used to spread heat fro m t he package case to the ambient surrounding temperature (r (c-a) ) . the composite of these two thermal resistances is r (j-a) , which represents the package thermal resistance with at least 1 square inch of copper ground p lane. from this figure, which for the MIC23450 is 30c/w, we can calculate maximum internal power dissipation as shown in equation 7 : a) (j amb jmax max r t t pd ? ? = eq. 7 w here: t jmax = maximum junction temp (125c) t amb = ambient temperature r (j-a) = 30c/w as can be expected , the allowable dissipation tends towards zero as the ambient temperature increases towards the maximum operating junction temperature. the graph of pd max vs. ambient temperature could be drawn quite simply using this equation. however, a more useful measure is the maximum output current per regulator vs. ambient temperature. for this, we must first create an ?exchange rate? between power dissipation per regulator (p diss ) and its output current (i out ). an accurate measure of this functio n can utilize the efficiency curve , as illustrated in equation 8: ( ) 1 p p p p p out loss loss out out ? = + = eq. 8 where: = efficiency p out = i out .v out to arrive at the internal package dissipation p diss , one would need to remove the inductor loss p dcr which is not dis sipated within the package. this however, does not give a worst case figure, since efficiency is typically measured on a nominal part at nominal temperatures. the i out to p diss function we use therefore is a synthesized p diss which accounts for worst case values at maximum operating temperature, as shown in equation 9: ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + = in out dson_n in out dson_p 2 out diss v v 1 r v v r i p eq. 9 where: r dson_p = maximum r dson of the high side, p - channel switch at t jmax r dson_n = maximum r dson of the low side, n - channel switch at t jmax v out = o utput voltage, v in = input voltage since ripple current and switching losses are small with respect to resistive losses at maximum output current, they can be considered negligible for the purpose of this method, but could be included if required .
micrel, inc. MIC23450 december 2012 16 m9999 -1207 12 -a now we have a function describing p diss in terms of i out , we can substitute p diss with equation 7 to form the function of maximum output current i out max vs. ambient temperature t amb (equation 10) : ? ? ? ? ? ? ? ? ? + ? = ? in out dson_n in out dson_p a) (j amb jmax outmax v v 1 r v v r r t t i eq. 10 the curves shown in the characteristic curves section are plots of this function adjusted to account for 1, 2 or 3 regulators running simultaneously. hyperlight load mode each regulator in the MIC23450 uses a minimum on and off time proprietary control loop (patented by micre l). when the output voltage falls below the regulation threshold, the error comparator begins a switching cycle that turns the pmos on and keeps it on for the duration of the minimum - on- time. this increases the output voltage. if the output voltage is over the regulation threshold, then the error comparator turns the pmos off for a minimum - off - time until the output drops below the threshold. the nmos acts as an ideal rectifier that conducts when the pmos is off. using a nmos switch instead of a diode allows for lower voltage drop across the switching device when it is on. the asynchronous switching combination between the pmos and the nmos allows the control loop to work in discontinuous mode for light load operations. in discontinuous mo de, the MIC23450 wor ks in pulse - frequency modulation (pfm) to regulate the output. as the output current increases, the off - time decreases, thus provides more energy to the output. this switching scheme improves the efficiency of MIC23450 during light load currents by only sw itching when it is needed. as the load current increases, the MIC23450 goes into continuous conduction mode (ccm) and switches at a frequency centered at 3mhz. the equation to calculate the load when the MIC23450 goes into continuous conduction mode may be approximated in equation 11 : ? ? ? ? ? ? ? ? ? > f 2l d ) v (v i out in load eq. 11 as shown in equation 11 , the load at which the MIC23450 transitions from hyperlight load mode to pwm mode is a function of the input voltage (v in ), output voltage (v out ), duty cycle (d), induc tance (l) and frequency (f). as shown in figure 4 , as the output current increases, the switching frequency also increases until the mic 23450 goes from hyperlight load mode to pwm mode at approximately 120ma. the MIC23450 will switch at a relatively consta nt frequency around 3mhz once the output current is over 120ma. 0.1 1 10 100 1000 10000 0.0001 0.001 0.01 0.1 1 10 frequency (khz) output current (a) switching frequency vs. load current v out = 1.8v v in = 5v v in = 3v v in = 3.6v figure 4. sw frequency vs. output current multiple sources the MIC23450 provides all the pins necessary to operate the 3 regulators from independent sources. this can be useful in partiti oning power within a multi rail system. for example, it is possible that within a system, two supplies are available; 3.3v and 5v. the MIC23450 can be connected to use the 3.3v supply to provide two, low voltage outputs (e.g. 1.2v and 1.8v) and use the 5v rail to provide a higher output (e.g. 2.5v), resulting in the power blocks shown in figure 5. figure 5. multi - source power block diagram
micrel, inc. MIC23450 december 2012 17 m9999 -1207 12 -a typical application circuit bill of materials item part number manufacturer description qty. c1, c2, c3, c 11, c12, c13 c1608x5r 1e104 k tdk (1) ceramic capacitor, 0.1f, 6.3v, x5r, size 0603 6 grm188r60j 104k d murata (2) c4 eeufr1a221 panasonic ( 3 ) electrolytic capacitor, 220 f, 10v, size 6.3mm 1 c6, c7, c8, c5, c9, c10 c1608x5r0j475k tdk ceramic capacitor, 4. 7f, 6.3v, x5r, size 0603 6 grm188r60j475ke19d murata r1, r2, r3 crcw0 40251r0 fkea vishay ( 4 ) resistor, 51 ? , size 0402 3 r4 crcw04023013fkea vishay resistor, 301 k ? , size 0402 1 notes : 1. tdk: www.tdk.com . 2. murata tel : www.murata.com . 3. panasonic : www.panasonic.com . 4. vishay tel: www.vishay.com .
micrel, inc. MIC23450 december 2012 18 m9999 -1207 12 -a bill of materials (continued) item part number manufacture r description qty. r5 crcw04021583fkea vishay resistor, 158k ? , size 0402 1 r6 crcw04023163fkea vishay resistor, 316k ? , size 0402 1 r7 crcw04022213fkea vishay resistor, 221k ? , size 0402 1 r12 crcw04022743fkea vishay resistor, 274k ? , size 0402 1 r14 crc w04022943fkea vishay resistor, 294k ? , size 0402 1 r8, r9, r10, r11, r13, r15 crcw04021003fkea vishay resistor, 100k ? , size 0402 6 r16, r17, r18 crcw08050000fkea vishay resistor, 0 ? , size 0805 3 l1, l2, l3 vls3012st - 1r0n1r9 tdk 1h, 2a, 60m?, l3.0mm x w3.0mm x h1.0mm 3 lqh44pn1r0nj0 murata 1h, 2.8a, 50m?, l4.0mm x w4.0mm x h1.2mm u1 MIC23450 - aaayml micrel, inc ( 5 ) 3mhz pwm 2a buck regulator with hyperlight load 1 note : 5. micrel, inc.: ww w.micrel.com .
micrel, inc. MIC23450 december 2012 19 m9999 -1207 12 -a pcb layout recommendations top layer mid - layer 1
micrel, inc. MIC23450 december 2012 20 m9999 -1207 12 -a pcb layout recommendations (continued) mid - layer 2 bottom layer
micrel, inc. MIC23450 december 2012 21 m9999 -1207 12 -a package information 1 32- pin 5mm 5mm mlf note: 1. package information is correct as of the publication date. for updates and most current information, go to www.micrel.com .
micrel, inc. MIC23450 december 2012 22 m9999 -1207 12 -a 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 a s 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 micrel?s 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 us e as components in life support appliances, devices 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 th e body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant inj ury 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. ? 2012 micrel, incorporated.

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