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MIC23303 4mhz pwm 3a buck regulator with hyperlight load? and power good hyperlight load is a 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 september 6, 2013 090613 - 2.0 general description the MIC23303 is a high - efficiency 4mhz 3a synchronous buck regulator with hyperlight load ? mode, power good output indicator, and programmable soft - start. hyperlight load provides very high efficiency at light loads and ultra - fast tran sient response , which makes the MIC23303 perfectly suited for supplying 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 capacito rs. the tiny 3mm 3mm dfn package saves precious board space and requires only six external components. the MIC23303 is designed for use with a very small inductor, down to 0.33h, and an output capacitor as small as 10f that enables a total solution siz e less than 1mm in height. the MIC23303 has very low quiescent current of 24a and can achieve peak efficiency of 93% in continuous conduction mode. in discontinuous conduction mode, the MIC23303 can achieve 80 % efficiency at 1ma. the MIC23303 is availabl e in a 12- pin 3mm 3mm dfn package with an operating junction temperature range from ? 40 c to +125 c. datasheets and support documentation are available on micrel?s web site at : www.micrel.com . features ? input voltag e: 2. 7 v to 5.5v ? output voltage: down to 0.65 ? up to 3a output current ? up to 93% peak efficiency ? 80% typical efficiency at 1ma ? power good output ? programmable soft - start ? 24 a typical quiescent current ? 4mhz pwm operation in continuous mode ? ultra - fast transien t response ? low ripple output voltage ? 35mvpp ripple in hyperlight load mode ? 5mv output voltage ripple in full pwm mode ? fully - integrated mosfet switches ? 0.01 a shutdown current ? thermal - shutdown and current - limit protection ? 12- pin 3mm 3mm dfn ? ? 40 c to +125 c junction temperature range applications ? portable media/mp3 players ? portable navigation devices (gps) ? wifi/wimax/wibro modules ? digital cameras ? wireless lan cards ? portable applications typical application
micrel, inc. MIC23303 september 6, 2013 2 090613 - 2.0 ordering information part number marking code nominal output voltage junction temperature range package MIC23303yml wya adjustable ? 40 c to +125c 12- pin 3mm 3mm dfn ( 1 , 2 ) notes: 1. dfn is a green rohs compliant package. lead finish is nipdau. mold compound is halogen free. 2. dfn pin 1 identifier is . pin configuration 3mm x 3mm dfn (ml) (top view) pin description pin number (adjustable) pin name pin function 1, 2 sw switch (output): internal power mosfet output switches. 3 pg power good: open - drain output for the power good indicator. u se a pull - up resistor from this pin to a voltage source to detect a power good condition. 4 en enable (input): logic high enables operation of the regulator. logic low shut s down the device. do not leave floating. 5 sns sense: connect to v out as close to output capacitor as possible to sense output voltage. 6 fb feedback: connect a resistor divider from the output to ground to set the output voltage. 7 ss soft start: place a capacitor from this pin to ground to program the soft start time. do not leave floating, 2.2nf minimum c ss is required. 8 agnd analog ground: connect to central ground point where all high current paths meet (c in , c out , and pgnd ) for best operation. 9 avin supply voltage (power input): analog control circuitry. connect to pvin . 10, 11 pvin input voltage: connect a capacitor to ground to decouple the noise. 12 pgnd power ground . ep epad thermal pad: connect to ground plane for improved heat sinking.
micrel, inc. MIC23303 september 6, 2013 3 090613 - 2.0 absolute maximum ratings ( 3 ) supply voltage (v in ) .......................................... ? 0.3v to 6v sense voltage (v sns ) ........................................ ? 0.3v to v in output switch voltage (v sw ) ............................. ? 0.3v to v in enable input voltage (v en ) .. .............................. ? 0.3v to v in power good voltage (v pg ) ................................ ? 0.3v to v in storage temperature range .................... ? 65 c to +150 c lead temperature (soldering, 10s) ............................. 260 c esd rating ( 5) ................................................. esd sensitive operating ratings ( 4 ) supply voltage (v in ) ........................................ .2.7 v to 5.5v enable input voltage (v en ) .................................... 0v to v in sense voltage (v sns ) ..................................... 0.65v to 5.5 v junction temperature range (t j ) ...... . ? 40 c t j +125 c thermal resistance 3mm 3mm dfn - 12 ( ja ) ................................. 61 c/w 3mm 3mm dfn - 12 ( jc ) ................................. 27 c/w electrical characteristics ( 6 ) t a = 25c; v in = v en = 3.6v; v out =1.8v; l = 0.33 h; c out = 44f unless otherwise specified. bold values indicate ? 40c ? t j ? +125c, unless otherwise noted. parameter condition min . typ . max . units supply voltage range 2.7 5.5 v under v oltage lockout threshold (turn -on) 2.3 2.53 2.8 v under v oltage lockout hysteresis 275 mv quiescent current i out = 0ma, sns > 1.2 v out nominal 24 40 a shutdown current v en = 0v; v in = 5.5v 0.01 5 a output voltage accuracy v in = 3.6v if v outnom < 2.5v, i load = 20ma ? 2.5 +2.5 % v in = 4.5v if v outnom ?9, load = 20ma feedback regulation voltage i load = 20ma 0.604 0.62 0.635 v current limit sns = 0.9 v outnom 3.5 6.5 10 a output voltage line regulation v in = 3.6v to 5.5v if v outnom < 2.5v, i load = 20ma 0.3 %/v v in = 4.5v to 5.5v if v outnom ?9, load = 20ma output voltage load regulation 20ma < i load < 50 0ma, v in = 3.6v if v outnom < 2.5v 0.3 % 20ma < i load < 500ma, v in = 5.0v if v outnom ?9 20ma < i load < 1a, v in = 3.6v if v outnom < 2.5v 0.7 % 20ma < i load < 1a, v in = 5.0v if v outnom ?9 pwm switch on - resistance i sw = 100ma pmos i sw = ? 100ma nmos 0.075 0.055 switching frequency i out = 300ma 4 mhz maximum duty cycle ( 7 , 8 ) 80 85 % soft start time v out = 90%, c ss = 2.2nf 1.26 ms notes: 3. exceeding the absolute m aximum rating may damage the device. 4. the device is not guaranteed to function outside its operating rating. 5. 'hylfhvduh(6'vhqvlwlyh+dqgolqjsuhfdxwlrqvuhfrpphqghg+xpdqerg\prghon lqvhulhvzlwks) 6. specification for packaged product only. 7. the maximum duty cycle is limited by the fixed mandatory off time of 300ns. 8. guaranteed by design.
micrel, inc. MIC23303 september 6, 2013 4 090613 - 2.0 electrical characteristics ( 6 ) (continued) t a = 25c; v in = v en = 3.6v; v out =1.8v; l = 0.33 h; c out = 44f unle ss otherwise specified. bold values indicate ? 40c t j +125c, unless noted. parameter condition min . typ . max . units power good threshold (rising) moving fb from low to high relative to 0.62v (v fb ) 85 90 95 % power good threshold hysteresis moving fb from high to low relative to 0.62v (v fb ) 20 % p ower good delay time rising 160 s power good pull - down rpg = 5.1k from pg to vout 200 mv enable threshold the voltage on enable that ensures the part is on 0.4 0.9 1.2 v enable input current 0.1 2 a overtemperature shutdown 160 c overtempe rature shutdown hysteresis 20 c
micrel, inc. MIC23303 september 6, 2013 5 090613 - 2.0 typical characteristics efficiency vs. load 1.8 v out 0 10 20 30 40 50 60 70 80 90 100 0.0001 0.001 0.01 0.1 1 10 load current(a) efficiency (%) v in = 3.6v v in = 5v l = 0.33h c out = 44f efficiency vs. load 1.2 v out 0 10 20 30 40 50 60 70 80 90 100 0.0001 0.001 0.01 0.1 1 10 load current (a) efficiency (%) v in = 3.6v l = 0.33 h c out = 44f v in = 5v v in = 3v v out rise time vs css 1 10 100 1000 10000 100000 1000000 1000 10000 100000 1000000 css (pf) rise time (s) v in =3.6v current limit vs. input voltage 3.00 4.00 5.00 6.00 7.00 8.00 2.5 3.0 3.5 4.0 4.5 5.0 5.5 input voltage (v) current limit (a) v ou t = 1.8v l = 0.33 h c out = 44 f quiscent current vs. input voltage 10 12 14 16 18 20 22 24 26 28 30 2.5 3 3.5 4 4.5 5 5.5 input voltage (v) quiescent current (a) t case = 25c output voltage vs. input voltage 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 1.25 2.5 3 3.5 4 4.5 5 5.5 input voltage (v) output voltage (v) i out =20ma i out =1ma l = 0.33 h c out = 44 f output voltage vs. input voltage 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 1.25 2.5 3 3.5 4 4.5 5 5.5 input voltage (v) output voltage (v) i out =500ma l = 0.33 h c out = 44 f i out =2a output voltage (hll) vs. load current 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 1.25 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 load current (a) output voltage (v) v in =3.6v l = 33 h c out = 44 f output voltage (ccm) vs. load current 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 1.25 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 load current (a) output voltage (v) v in =3.6v l = 33h c out = 44f
micrel, inc. MIC23303 september 6, 2013 6 090613 - 2.0 typical characteristics (c ontinued) output voltage vs. temperature 1.75 1.76 1.77 1.78 1.79 1.80 1.81 1.82 1.83 1.84 1.85 -40 -20 0 20 40 60 80 100 120 temperature (c) output voltage (v) v in = 3.6v l = 0.33 h c out = 44f i out = 20ma pg delay time vs. input voltage 40 60 80 100 120 140 160 2.5 3.0 3.5 4.0 4.5 5.0 5.5 input voltage (v) pg delay (s) pg rising pg falling pg thresholds vs. input voltage 65 70 75 80 85 90 95 2.5 3.0 3.5 4.0 4.5 5.0 5.5 input voltage (v) pg threshold (% of v ref ) pg rising pg falling undervoltage lockout vs. temperature 2.0 2.1 2.2 2.3 2.4 2.5 2.6 -40 -20 0 20 40 60 80 100 120 temperature (c) uvlo (v) uvlo off uvlo on enable threshold vs. input voltage 0.5 0.6 0.7 0.8 0.9 1.0 1.1 2.5 3.0 3.5 4.0 4.5 5.0 5.5 input voltage (v) en threshold (v) t case =25c enable thresholds vs. temperature 0.7 0.75 0.8 0.85 0.9 0.95 1 -40 -20 0 20 40 60 80 100 120 140 temperature (c) en threshold (v) feedback voltage vs. temperature 0.59 0.6 0.61 0.62 0.63 0.64 0.65 -40 -20 0 20 40 60 80 100 120 temperature (c) feedback voltage (v) v in = 2.7v v in = 5v shutdown current vs. temperature 1 10 100 1000 -40 -20 0 20 40 60 80 100 120 temperature (c) shutdown current (na) v in =5.5v v en =0v switching frequency vs. load current 0.1 1 10 100 1000 10000 0.0001 0.001 0.01 0.1 1 10 load current (a) sw frequency (khz) v in = 5v v in = 3v v out = 1.8v l = 0.33 h c out = 44 f
micrel, inc. MIC23303 september 6, 2013 7 090613 - 2.0 functional characteristics
micrel, inc. MIC23303 september 6, 2013 8 090613 - 2.0 functional characteristics (c ontinue d)
micrel, inc. MIC23303 september 6, 2013 9 090613 - 2.0 func tional characteristics (continued)
micrel, inc. MIC23303 september 6, 2013 10 090613 - 2.0 functional diagram figure 1 . simplified MIC23303 functional block diagram
micrel, inc. MIC23303 september 6, 2013 11 090613 - 2.0 functional description pvin the input supply (pvin) provides power to the internal mosfets for the s witch mode regulator section. the vin operating range is 2. 7 v to 5.5v so an input capacitor, with a minimum voltage rating of 6.3v, is recommended. due to the high switching speed, a minimum 4.7f bypass capacitor placed close to pvin and the power ground (pgnd) pin is required. refer to the pcb layout recommendations for details. avin analog vin (avin) provides power to the internal control and analog supply circuitry. avin and pvin must be tied together. careful l ayout should be considered to ensure high frequency switching noise caused by pvin is reduced before reaching avin. a 1 f capacitor as close to avin as possible is recommended. see pcb layout recommendations for de tail s . 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 nominal 0.01a. MIC23303 features external soft - start circuitry via the so ft start (ss) pin that reduces in - rush current and prevents the output voltage from overshooting when en is driven logic high. do not leave the en pin floating. sw the switch (sw) connects directly to one end of the inductor and provides the current path d uring 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 whenever possible. sns the sense (sns) pi n 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 pcb 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 pcb layout recommenda tions for more details. pgnd the power ground pin is the ground path for the high current in pwm mode. the current loop for the power ground should be as small as possible and separate from the analog ground (agnd) loop as applicable. refer to the pcb layout recommendations for more details. pg the power good (pg) pin is an open - drain output that 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 . ss the soft start (ss) pin is used to control the output voltage ramp - up time. the approximate equation for the ramp time in seconds is 250 10 3 ln(10) c ss . for example, for c ss = 2.2nf, t rise ~ 1.26ms . see the typical characteristics curve for a graphical guide. the minimum recommended value for c ss is 2.2nf. fb the feedback (fb) pin is provided for the adjustable voltage option (no internal connection for fixed options ). this is the control input for programming the output voltage. 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 0 .65v and 3.6v using the following equation: ? 1 ? ? r4 r3 1 v v ref out where: r3 is the top resistor, r4 is the bottom resistor. example feedback resistor values: v out r3 r4 1.2v 274k 294k 1.5v 316k 221k 1.8v 560k 294k 2.5v 324k 107k 3.3v 464k 107k
micrel, inc. MIC23303 september 6, 2013 12 090613 - 2.0 application information the MIC23303 is a high - performance dc - to - dc step down regulator offering a small solution size. supporting an output current up to 3a inside a tiny 3mm x 3mm dfn package, the ic requires only six external components while meeting to day?s miniature portable electronic device needs. using the hyperlight load switching scheme, the MIC23303 is able to maintain high efficiency throughout the entire load range while providing ultra - fast load transient response. the following sections provi de additional device application information. input capacitor a 4.7f ceramic capacitor or greater should be placed close to the pvin pin and pgnd pin for bypassing. a murata grm188r60j475me19d, size 0603, 4.7f ceramic capacitor is recommended 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 reduc es their ability to filter out high frequency noise. output capacitor the MIC23303 is designed for use with a 10f or greater ceramic output capacitor. increasing 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 grm21br60j226me39l, size 0805, 22f ceramic capacitor is recommended based upon performance, size and cost. two of these capacitors i n parallel will decrease esr, resulting in decreased output voltage ripple. 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 temperature 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 re sistance (dcr) the MIC23303 is designed for use with a 0.33h to 1.0h inductor. for faster transient response and greater efficiency, a 0.33h inductor will yield the best result. to achieve lower output voltage ripple, a higher value inductor such as a 1h can be used. however, a greater value inductor, when operating in low load mode will result in a higher operating frequency. this effect with increased dcr will result in a less efficient design. maximum current ratings of the inductor are generally g iven in two methods; permissible dc current and saturation current. permissible dc current can be rated either for a 40c temperature rise or a 10% to 20% loss in inductance. ensure that the inductor selected can handle the maximum operating current. when saturation current is specified, make sure that there are enough margins that the peak current does not cause the inductor to saturate. peak current can be calculated as follows: ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + = l f 2 /v v 1 v i i in out out out peak as shown by the calculation above, 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 current. as input voltage increases, the peak current is somewhat limited by constant off time control . the size of the inductor depends on the requirements of the application. refer to the typical application schematic 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 r ipple current and the load current.
micrel, inc. MIC23303 september 6, 2013 13 090613 - 2.0 figure 2 . hyperlight load (hll) and continuous conduction mode (ccm) switching diagram figure 2 shows the signals for high - side switch drive (hsd) for ton control, the i nductor current and the low - side switch drive (lsd) for toff control. in hll mode, the inductor is charged with a fixed ton pulse on the high - side switch (hsd). after this, the lsd is switched on and current falls at a rate v out /l. th e controller remains in hll mode while the inductor falling current is detected to cross approximately 300ma. when the lsd (or toff) time reaches its minimum and the inductor falling current is no longer able to reach this 300ma threshold, the part is in c cm mode and switching at a virtually constant frequency. compensation the MIC23303 is designed to be stable with a 0.33h to 1.0h inductor with a minimum 10f ceramic (x5r) output capacitor. the total feedback resistance should be kept around 500k? to reduce the i 2 r losses through the feedback resistor network, improving ef ficiency. a feed - forward capacitor (cff) of 33pf is recommended across the top feedback resistor to reduce the effects of parasitic capacitance and improve transient performance. duty cycle the typical maximum duty cycle of the MIC23303 is 85 %. 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 u ? ? 1 ? u u maintaining high efficiency serves two purposes. it reduces power dissipation in the power supply, reducing the nee d for heat sinks and thermal design considerations , and it reduces consumption of current for battery - powered applications. reduced current draw from a battery increases the devices operating time and is critical in handheld devices. there are two types o f 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 s witch c urrent squared. during the off cycle, the low side n - channel mosfet conducts, also dissipating power. device operating current also reduces efficiency. the product of the quiescent (operating) current and the supply voltage represents another dc loss. th e current required to drive the gates on and off at a constant 4mhz frequency and the switching transitions make up the switching losses. efficiency vs. load 1.8 v out 0 10 20 30 40 50 60 70 80 90 100 0.0001 0.001 0.01 0.1 1 10 load current(a) efficiency (%) v in = 3.6v v in = 5v l = 0.33h c out = 44f figure 3 . efficiency under load figure 3 shows an efficiency curve. from no load to 100ma, efficiency losses are dominated by quiescent current losses, gate drive , and transition losses. by using hyperlight load mode, the MIC23303 is able to maintain high efficiency at low output currents. over 300ma, 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 devi ce. all but the inductor losses are inherent to the device. when dealing with inductor losses , inductor selection becomes increasingly critical in efficiency calculations.
micrel, inc. MIC23303 september 6, 2013 14 090613 - 2.0 as the inductors are reduced in size, the dc resistance (dcr) can become quite sig nificant. the dcr losses can be calculated as follows: p dcr = i out 2 dcr 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 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + ? = efficiency loss due to dcr is minimal at light loads and gains s ignificance as the load is increased. inductor selection becomes a trade - off between efficiency and size in this case. hyperlight load mode MIC23303 uses a minimum on and off time proprietary control loop (patented by micrel). 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 t he 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 th e 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 mode, the MIC23303 works 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 MIC23303 during light load currents by only switching when it is needed. as the load current increases, the MIC23303 goes into continuous conduction mode (ccm) and switches at a frequency centered at 4mhz. the equation to calculate the load when the MIC23303 goes into continuous conduction mode may be approximated by the following fo rmula: ? ? ? ? ? ? ? ? ? > f 2l d ) v (v i out in load as shown in the previous equation, the load at which the MIC23303 transitions from hyperlight load mode to pwm mode is a function of the input voltage (v in ), output voltage (v out gxw\ f\foh ' hiilflhqf\ lqgxfwdqfh l) and frequency (f). as shown in figure 4 , as the o utput c urrent increases, the switching frequency also increases until the MIC23303 goes from hyperlight load mode to pwm mode at approximately 300ma. the MIC23303 will switch at a relatively constant frequency around 4mhz once the output current is over 300ma. switching frequency vs. load current 0.1 1 10 100 1000 10000 0.0001 0.001 0.01 0.1 1 10 load current (a) sw frequency (khz) v in =5v v in =3.3v v out = 1.8v l = 0.33h c out = 44f figure 4 . sw frequency vs. output current power dissipation c onsiderations as with all power devices, the ultimate current rati ng of the output is limited by the thermal properties of the package and the pcb it is mounted on. there is a simple, ohm?s law type relationship between thermal resistance, power dissipation and temperature which are analogous to an electrical circuit: figure 5 . ohm?s law description
micrel, inc. MIC23303 september 6, 2013 15 090613 - 2.0 from this simple circuit we can calculate v x if we know i source , v z, and the resistor values, r xy and r yz , using the equation: ( ) z yz xy source x v r r i v + + = thermal circuits can be considered using th ese same rules and can be drawn similarly replacing current sources with p ower dissipation (in watts), r esistance with t hermal r esistance (in c/w) and v oltage sources with temperature (in c). figure 6 . thermal circuit descript ion now replacing the variables in the equation for v x , we can find the junction temperature (t j ) from power dissipation, ambient temperature , and the known thermal resistance of the pcb (r ca ) and the package (r jc ). ( ) amb ca jc diss j t r r p t + + = as can be s een in the diagram, total thermal resistance r ja = r j c + r ca . hence this can also be written: ( ) amb ja diss j t r p t + = since effectively all of the power losses (minus the inductor losses) in the converter are dissipated within the MIC23303 package, p diss can be calculated thus: dcr i ) 1 1 ( p p 2 out out diss ? ? ? ? ? ? ? ? = where: = efficiency taken from efficiency curves and dcr = inductor dcr. r jc and r ja are found in the operating ratings section of the datasheet. where the reel board area differs from 1 in square, r ca (the pcb thermal resistance) values for various pcb copper areas can be taken from figure 7 below. this graph is taken from designing with low dropout voltage regulato rs , which is available from the micrel website (ldo application hints). example: a MIC23303 is intended to drive a 2a load at 1.8v and is placed on a printed circuit board which has a ground plane area of at least 25mm square. the voltage source is a li - ion battery with a lower operating threshold of 3v and the ambient temperature of the assembly can be up to 50 c. summary of variables: i out = 2a v out = 1.8v v in = 3v to 4.2v t amb = 50 c r ja = 61 c/w from d atasheet @ 2a = 85% (worst case @ 5v from figure 3 )
micrel, inc. MIC23303 september 6, 2013 16 090613 - 2.0 figure 7 . pcb thermal resistance versus pcb copper area ( ) ? ? ? ? ? ? ? ? ? = m 20 2 ) 1 85 . 0 1 ( 2 8 . 1 p 2 diss = 0.56w the worst case switch an d inductor resistance will increase at higher temperatures, so a margin of 20% can be added to account for this. p diss = 0.56 1.2 = 0 .67w therefore: t j = 0.67w. (61 c/w ) + 50 c t j = 91 c this is well below the maximum 125 c.
micrel, inc. MIC23303 september 6, 2013 17 090613 - 2.0 typical application schem atic bill of materials item part number manufacturer d escription qty . c1 06036d475kat2a avx ( 9 ) 4.7 f/6.3v, x5r, 0603 1 grm188r60j475me19d murata ( 10 ) c1608x5r 0j475m tdk ( 11 ) c2 06035c222kat2a avx 2.2nf/50v, x7r, 0603 1 grm188r71h222ma01d murata c1608x7r1h222k tdk c3, c8 08056d226mat2a avx 22 f/6.3v, x5r, 0805 1 grm21br60j226me39l murata c2012x5r0j226m t dk notes: 9. avx: www.avx.com . 10. murata : www.murata.com . 11. tdk: www.tdk.com .
micrel, inc. MIC23303 september 6, 2013 18 090613 - 2.0 bill of materials (continued) item part n umber manufacturer d escription qty . c4 06035a330kat2a avx 33pf/50v, 0603 1 grm1885c1h330ja01d murata c6 06036d105kat2a avx 1 f/6.3v, x5r, 0603 1 grm188r60j105ka01d murata c1608x5r0j105k tdk c7 06035d104kat2a avx 0.1 f/6.3v, x5r, 0603 1 grm188r7 1h104ka930 murata c1608x5r1h104k tdk l1 0520cdmcdsnp - r33mc sumida ( 12 ) 0.33 h/5.6a, 8m? 1 744373240033 wurth ( 13 ) 0.33 h/8.0a, 8.6m? r1, r2 crcw060310k0fkea vishay/dale ( 14 ) 10k,1%, 1/10w, 0603 2 r3 crcw0603560kfkea vishay/dale 560k,1%, 1/10w, 0 603 1 r4 crcw0603294kfkea vishay/dale 294k,1%, 1/10w, 0603 1 r5 crcw060310r0fkea vishay/dale 10?,1%, 1/10w, 0603 1 ic1 MIC23303y ml micrel, inc ( 15) 4mhz 3a buck regulator with hyperl ight load mode and power good 1 notes: 12. sumida: www.sumida.com . 13. wurth: www.we - online.com . 14. vishay: www.vishay.com . 15. micrel, inc.: www .micrel.com .
micrel, inc. MIC23303 september 6, 2013 19 090613 - 2.0 pcb layout recommendations top layer bottom layer
micrel, inc. MIC23303 september 6, 2013 20 090613 - 2.0 package information ( 16) 12- pin 3mm x 3mm dfn (ml ) note: 16. package information is correct as of the publication date. for updates and mo st current information, go to www.micrel.com .
micrel, inc. MIC23303 september 6, 2013 21 090613 - 2.0 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 this 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 a nd 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 prod ucts, 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 infrin gement 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 i n 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 si gnificant 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 a nd purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2 0 02 micrel, incorporated.

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