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1 for more information www.linear.com/ltm8021 typical a pplica t ion fea t ures a pplica t ions descrip t ion 36v in , 500ma step-down dc/dc module the lt m ? 8021 is a 36v in 500ma, step-down dc/dc module ? . included in the package are the switching controller, power switches, inductor, and all support components. operating over an input voltage range of 3v to 36v , the l tm8021 supports an output voltage range of 0.8v to 5v, set by a single resistor. only an output and bulk input capacitor are needed to fnish the design. the low profle package (2.82mm) enables utilization of unused space on the bottom of pc boards for high den - sity point of load regulation. a built-in soft-start timer is adjustable with just a resistor and capacitor . the l tm8021 is packaged in a thermally enhanced, compact (11.25mm 6.25mm) and low profle (2.82mm) overmolded land grid array (lga) package suitable for automated assembly by standard surface mount equipment. the ltm8021 is rohs compliant. 7v in to 36v in , 5v/500ma module regulator n complete switch mode power supply n wide input voltage range: 3v to 36v n 500ma output current n 0.8v to 5v output voltage n fixed 1.1mhz switching frequency n current mode control n (e4) rohs compliant package with gold pad finish n programmable soft-start n tiny, low profle (11.25mm 6.25mm 2.82mm) sur face mount lga package n automotive battery regulation n power for portable products n distributed supply regulation n industrial supplies n wall transformer regulation effciency and power loss ltm8021 8021 ta01a v in * 7v to 36v v out 5v at 500ma 1f 2.2f 19.1k run/ss in gnd adj bias out *running voltage range. please refer to the applications information section for start-up details. 0 power loss (mw) 100 200 300 450 400 50 150 250 350 8021 ta01b load current (ma) 1.00 30 efficiency (%) 40 50 70 60 10.00 100.00 90 80 1000.00 power loss efficiency l , lt, ltc, ltm, module, polyphase, linear technology and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. ltm8021 8021fd
2 for more information www.linear.com/ltm8021 a bsolu t e maxi m u m r a t ings v in , run/ss voltage ................................................. 40v r un/ss above v in ...................................................... 3v ad j voltage ................................................................ 5v b ias voltage ............................................................... 7v v out voltage ............................................................. 10 v internal operating temperature range (note 2) ....................................... C 40c to 125c maximum solder temperature .............................. 26 0c storage temperature range .................. C 55c to 125c (note 1) symbol parameter conditions min typ max units v in input dc voltage v run/ss = 5v, r adj = open 3 36 v v out output dc voltage 0 < i out < 500ma; r adj open 0 < i out < 500ma; r adj = 19.1k, 0.1% 0.8 5 v v r adj(min) minimum allowable r adj note 3 18 kw i lk leakage from in to out run/ss = v bias = 0v, r adj open 2.7 6 a i out continuous output dc current 5v v in 36v, v bias = v out 0 500 ma i q(vin) quiescent current into v in run/ss = 0.2v, v bias , r adj open not switching 0.1 1.5 1 2.5 a ma i q(bias) quiescent current into bias not switching 0.15 a ?v out /v out line regulation 5v v in 36v, i out = 500ma r adj = open 0.5 % ?v out /v out load regulation v in = 24v, 0 i out 500ma, v bias = v out 0.35 % e lec t rical c harac t eris t ics the l denotes the specifcations which apply over the full operating temperature range, otherwise specifcations are at t a = 25c, v in = 10v, v run/ss = 10v, v bias = 3v, r adj = 31.6k. or d er in f or m a t ion p in c on f igura t ion v in bank 1 v out bank 2 gnd bank 3 adj bias run/ss h ba dc 5 1 2 3 4 e f lga package 35-lead (11.25mm 6.25mm 2.82mm) g top view t jmax = 125c, ja = 36.9c/w, jb = 20.9c/w, weight = 0.49g jc(top) = 41.74c/w, jc(bottom) = 17.8c/w part number pad or ball finish part marking* package type msl rating tempera ture range (note 2) device finish code ltm8021ev#pbf au (rohs) ltm8021v e4 lga 3 C40c to 125c ltm8021iv#pbf au (rohs) ltm8021v e4 lga 3 C40c to 125c consult marketing for parts specifed with wider operating temperature ranges. *device temperature grade is indicated by a label on the shipping container. pad or ball fnish code is per ipc/jedec j-std-609. ? terminal finish part marking: www.linear.com/leadfree ? recommended lga and bga pcb assembly and manufacturing procedures: www.linear.com/umodule/pcbassembly ? lga and bga package and t ray drawings: www .linear.com/packaging ltm8021 8021fd
3 for more information www.linear.com/ltm8021 e lec t rical c harac t eris t ics note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: the ltm8021e is guaranteed to meet performance specifcations from 0c to 125c internal. specifcations over the full C40c to 125c internal operating temperature range are assured by design, the l denotes the specifcations which apply over the full operating temperature range, otherwise specifcations are at t a = 25c, v in = 10v, v run/ss = 10v, v bias = 3v, r adj = 31.6k. characterization and correlation with statistical process controls. the ltm8021i is guaranteed to meet specifcations over the full C40c to 125c internal operating temperature range. note that the maximum internal temperature is determined by specifc operating conditions in conjunction with board layout, the rated package thermal resistance and other environmental factors. note 3: guaranteed by design. symbol parameter conditions min typ max units v out(dc) dc output voltage v in = 24v, 0 i out 500ma r adj = 31.6k, 0.1% 3.3 v v out(ac_rms) output voltage ripple (rms) v in = 24v, i out = 250ma c out = 2.2f, v bias = v out 1 mv f sw switching frequency i out = 500ma 0.9 1.1 1.3 mhz i osc short-circuit output current v in = 36v, v bias = v out = 0v 900 ma i isc short-circuit input current v in = 36v, v bias = v out = 0v 25 ma adj voltage at adj pin r adj open l 0.79 0.80 0.83 v v bias(min) minimum bias voltage for proper operation i out = 500ma 2.2 3 v i adj current out of adj pin v out = 5v, v adj = 0v, run/ss = 0v 50 a i run/ss run/ss pin current v run/ss = 2.5v, r adj open 23 a v ih(run/ss) run/ss input high voltage r adj open, i out = 500ma 1.6 v v il(run/ss) run/ss input low voltage r adj open, i out = 500ma 0.5 v r fb internal feedback resistor run/ss = v bias = v adj = 0v 100 kw ltm8021 8021fd
4 for more information www.linear.com/ltm8021 typical p er f or m ance c harac t eris t ics effciency vs load current effciency vs load current effciency vs load current effciency vs load current i bias vs load current i bias vs load current i bias vs load current i bias vs load current t a = 25 c, unless otherwise noted load current (ma) 0 efficiency (%) 60 85 90 100 200 300 50 75 55 80 45 40 70 65 50 150 400 500 250 350 450 8021 g01 v in = 36v v in = 24v v in = 12v v in = 5v v out = 1.8v load current (ma) 0 efficiency (%) 60 85 90 100 200 300 50 75 55 80 70 65 50 150 400 500 250 350 450 8021 g02 v in = 36v v in = 24v v in = 12v v in = 5v v out = 2.5v load current (ma) 0 efficiency (%) 60 85 90 100 200 300 75 55 80 70 65 50 150 400 500 250 350 450 8021 g03 v in = 36v v in = 24v v in = 12v v in = 5v v out = 3.3v load current (ma) 0 efficiency (%) 60 85 90 100 200 300 75 80 70 65 50 150 400 500 250 350 450 8021 g04 v in = 36v v in = 24v v in = 12v v out = 5v load current (ma) 0 0 bias current (ma) 2 4 6 100 200 300 400 500 1 3 5 600 8021 g05 v in = 24v v in = 12v v in = 5v v in = 3.4v v out = 0.8v load current (ma) 0 0 bias current (ma) 2 4 6 100 200 300 400 500 8 1 3 5 7 9 600 8021 g06 v in = 24v v in = 12v v in = 5v v in = 3.4v v out = 1.8v load current (ma) 0 0 bias current (ma) 2 4 6 100 200 300 400 500 8 1 3 5 7 600 8021 g07 v in = 24v v in = 12v v in = 5v v out = 2.5v load current (ma) 0 0 bias current (ma) 2 4 6 100 200 300 400 500 8 10 1 3 5 7 9 600 8021 g08 v in = 24v v in = 12v v in = 5v v out = 3.3v ltm8021 8021fd
5 for more information www.linear.com/ltm8021 typical p er f or m ance c harac t eris t ics input current vs output current input current vs output current input quiescent current vs input voltage minimum input running voltage vs output voltage t a = 25 c, unless otherwise noted input current vs output current output short-circuit current vs input voltage output current (ma) 0 input current (ma) 100 350 400 100 200 300 0 250 50 300 200 150 50 150 400 500 250 350 450 8021 g09 v in = 5v v out = 1.8v v out = 3.3v v out = 2.5v output current (ma) 0 input current (ma) 100 300 100 200 300 0 250 50 200 150 50 150 400 500 250 350 450 8021 g10 v in = 12v v out = 1.8v v out = 5v v out = 3.3v v out = 2.5v output current (ma) 0 input current (ma) 40 140 100 200 300 0 100 20 120 80 60 50 150 400 500 250 350 450 8021 g11 v in = 24v v out = 1.8v v out = 5v v out = 3.3v v out = 2.5v input voltage (v) 0 input quiescent current (a) 1000 3000 10 20 30 0 2500 500 2000 1500 5 15 40 25 35 8021 g12 v o = 3.3v output voltage (v) 0 0 input voltage (v) 2 4 6 1 2 3 4 5 1 3 5 7 6 8021 g13 i out = 500ma input voltage (v) 4 output current (ma) 840 860 880 32 820 800 12 20 8 16 24 36 28 740 720 780 900 760 8021 g14 v out = 3.3v radiated emissions frequency (mhz) 0 emissions level (dbv/m) 50 70 90 800 8021 g15 30 10 40 60 80 20 0 ?10 200 400 600 1000 36v in 5v out full load cispr22 class b limit ltm8021 8021fd
6 for more information www.linear.com/ltm8021 p in func t ions v in (bank 1): the v in pin supplies current to the ltm8021s internal regulator and to the internal power switch. this pin must be locally bypassed with an external, low esr capacitor of at least 1f. v out (bank 2): power output pins. an external capacitor is connected from v out to gnd in most applications. apply output load between these pins and gnd pins. bias (pin h3): the bias pin connects to the internal boost schottky diode and to the internal regulator. tie to v out when v out > 3v or to another dc voltage greater than 3v otherwise. when bias > 3v the internal circuitry will be powered from this pin to improve effciency. main regulator power will still come from v in . run/ss (pin a1): tie run/ss pin to ground to shut down the ltm8021. tie to 1.6v or more for normal operation . if the shutdown feature is not used, tie this pin to the v in pin. the run/ss also provides soft-start and frequency foldback. to use the soft-start function, connect a resistor and capacitor to this pin. do not allow the run/ss pin to rise above v in . see the applications information section. gnd (bank 3): the gnd connections serve as the main signal return and the primary heat sink for the ltm8021. tie the gnd pins to a local ground plane below the ltm8021 and the circuit components. return the feedback divider to this signal. adj (pin a2): the ltm8021 regulates its adj pin to 0.8v. connect the adjust resistor from this pin to ground. the value of r adj is given by the equation, r adj = 80/ (v out C 0.8), where r adj is in k. v in 8021 bd bias current mode controller v out 10f 15pf 10h 0.1f run/ss 100k 1% adj gnd b lock diagra m ltm8021 8021fd
7 for more information www.linear.com/ltm8021 o pera t ion applica t ions in f or m a t ion for most applications, the design process is straight forward, summarized as follows: 1. refer to table 1 for the row that has the desired input range and output voltage. 2. apply the recommended c in , c out and r adj values. 3. connect bias as indicated. while these component combinations have been tested for proper operation, it is incumbent upon the user to verify proper operation over the intended system s line, load and environmental conditions. if the desired output voltage is not listed in table 1, set the output by applying an r adj resistor whose value is given by the equation, r adj = 80/(v out C 0.80), where r adj is in k and v out is in volts. verify the ltm8021s operation over the systems intended line, load and environmental conditions. minimum duty cycle the ltm8021 has a fxed 1.1mhz switching frequency. for any given output voltage, the duty cycle falls as the input voltage rises. at very large v in to v out ratios, the duty cycle can be very small. because the ltm8021s internal controller ic has a minimum on-time, the regulator will skip cycles in order to maintain output voltage regulation. this will result in a larger output voltage ripple and possible disturbances during recovery from a transient load step. the component values provided in table 1 allow for skip cycle operation, but hold the resultant output ripple to around 50mv, or less. if even less ripple is desired, then more output capacitance may be necessary. adding a feed - forward capacitor has been empirically shown to modestly extend the input voltage range to where the l tm8021 does not skip cycles. apply the feedforward capacitor between the v out pins and adj. this injects perturbations into the control loop, therefore, values larger than 50pf are not recommended. a good value to start with is 12pf. the ltm8021 is a standalone nonisolated step-down switching dc/dc power supply. it can deliver up to 500ma of dc output current with only bulk external input and output capacitors. this module provides a precisely regulated output voltage programmable via one external resistor from 0.8v dc to 5v dc . the input voltage range is 3v to 36v. given that the ltm8021 is a step-down converter, make sure that the input voltage is high enough to support the desired output voltage and load current. please refer to the simplifed block diagram. the ltm8021 contains a current mode controller, power switching element, power inductor, power schottky diode and a modest amount of input and output capacitance. with its high performance current mode controller and internal feedback loop compensation, the ltm8021 module has suffcient stability margin and good transient perfor - mance under a wide range of operating conditions with a wide range of output capacitors, even all ceramic ones (x5r or x7r). current mode control provides cycle-by-cycle fast current limit, and automatic current limiting protects the module in the event of a short cir cuit or overload fault. the ltm8021 is based upon a 1.1mhz fxed frequency pwm current mode controller, equipped with cycle skip capability for low voltage outputs or light loads. a frequency foldback scheme helps to protect internal components from overstress under heavy and short-circuit output loads. the drive circuit for the internal power switching element is powered through the bias pin. power this pin with at least 3v. ltm8021 8021fd
8 for more information www.linear.com/ltm8021 a pplica t ions i n f or m a t ion table 1. recommended component values and confguration v in range v out c in c out r adj bias 3.4v to 36v 0.8v 4.7f 100f 1210 8.2m 3v to 7v 3.4v to 36v 1.2v 4.7f 100f 1210 200k 3v to 7v 3.4v to 36v 1.5v 4.7f 100f 1210 115k 3v to 7v 3.4v to 36v 1.8v 2.2f 100f 1210 78.7k 3v to 7v 3.5v to 36v 2v 2.2f 100f 1210 66.5k 3v to 7v 4v to 36v 2.2v 1f 22f 1206 57.6k 3v to 7v 4v to 36v 2.5v 1f 10f 0805 47.5k 3v to 7v 5v to 36v 3.3v 1f 4.7f 0805 32.4k v out 7v to 36v 5v 1f 2.2f 0805 19.1k v out 3.5v to 32v C3.3v 1f 4.7f 0805 32.4k gnd 3.75v to 31v C5v 1f 4.7f 0805 19.1k gnd 3.4v to 15v 0.8v 4.7f 100f 1210 8.2m 3v to 7v 3.4v to 15v 1.2v 4.7f 100f 1210 200k 3v to 7v 3.4v to 15v 1.5v 4.7f 47f 1206 115k 3v to 7v 3.4v to 15v 1.8v 2.2f 47f 1206 78.7k 3v to 7v 3.5v to 15v 2v 2.2f 22f 1206 66.5k 3v to 7v 4v to 15v 2.2v 1f 22f 1206 57.6k 3v to 7v 4v to 15v 2.5v 1f 10f 0805 47.5k 3v to 7v 5v to 15v 3.3v 1f 2.2f 0805 32.4k v out 7v to 15v 5v 1f 1f 0805 19.1k v out 9v to 24v 0.8v 1f 100f 1210 open 3v to 7v 9v to 24v 1.2v 1f 100f 1210 200k 3v to 7v 9v to 24v 1.5v 1f 47f 1206 115k 3v to 7v 9v to 24v 1.8v 1f 47f 1206 78.7k 3v to 7v 9v to 24v 2v 1f 22f 1206 66.5k 3v to 7v 9v to 24v 2.2v 1f 22f 1206 57.6k 3v to 7v 9v to 24v 2.5v 1f 10f 0805 47.5k 3v to 7v 9v to 24v 3.3v 1f 2.2f 0805 32.4k v out 9v to 24v 5v 1f 1f 0805 19.1k v out 18v to 36v 0.8v 1uf 100f 1210 open 3v to 7v 18v to 36v 1.2v 1uf 100f 1210 200k 3v to 7v 18v to 36v 1.5v 1uf 100f 1210 115k 3v to 7v 18v to 36v 1.8v 1uf 100f 1210 78.7k 3v to 7v 18v to 36v 2v 1uf 100f 1210 66.5k 3v to 7v 18v to 36v 2.2v 1uf 22f 1206 57.6k 3v to 7v 18v to 36v 2.5v 1uf 10f 0805 47.5k 3v to 7v 18v to 36v 3.3v 1uf 4.7f 0805 32.4k v out 18v to 36v 5v 1uf 2.2f 0805 19.1k v out ltm8021 8021fd
9 for more information www.linear.com/ltm8021 capacitor selection considerations the c in and c out capacitor values in table 1 are the minimum recommended values for the associated oper - ating conditions. applying capacitor values below those indicated in table 1 is not recommended, and may result in undesirable operation. using larger values is generally acceptable, and can yield improved dynamic response or fault recover y, if it is necessary. again, it is incumbent upon the user to verify proper operation over the intended systems line, load and environmental conditions. ceramic capacitors are small, robust and have very low esr. however, not all ceramic capacitors are suitable. x5r and x7r types are stable over temperature and ap - plied voltage and give dependable service. other types, including y5v and z5u have very large temperature and voltage coeffcients of capacitance. in an application cir - cuit they may have only a small fraction of their nominal capacitance resulting in much higher output voltage ripple than expected. ceramic capacitors are also piezoelectric. at light loads, the l tm8021 skips switching cycles in order to maintain regulation. the resulting bursts of current can excite a ceramic capacitor at audio frequencies, generating audible noise. if this audible noise is unacceptable, use a high performance electrolytic capacitor at the output. this output capacitor can be a parallel combination of a 1f ceramic capacitor and a low cost electrolytic capacitor. a fnal precaution regarding ceramic capacitors con - cerns the maximum input voltage rating of the ltm8021. a ceramic input capacitor combined with trace or cable inductance forms a high q (under damped) tank cir cuit. if the l tm8021 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possi - bly exceeding the devices rating. this situation is easily avoided; see the hot-plugging safely section. minimum input voltage the l tm8021 is a step-down converter, so a minimum amount of headroom is required to keep the output in regulation. for most applications at full load, the input must be about 1.5v above the desired output. in addition, it takes more input voltage to turn on than is required for continuous operation. this is shown in figure 1. a pplica t ions i n f or m a t ion figure 1. the ltm8021 requires more voltage to start than to run load current (a) 0.001 2.0 input voltage (v) 3.0 4.0 5.0 0.01 0.1 6.0 2.5 3.5 4.5 5.5 1 8021 f01 v out = 3.3v to start to run load current (a) 0.001 2 input voltage (v) 3 4 6 5 0.01 0.1 8 7 1 v out = 5v run/ss enabled run/ss enabled to start to run ltm8021 8021fd
10 for more information www.linear.com/ltm8021 a pplica t ions i n f or m a t ion figure 2. to soft-start the ltm8021, add a resistor and capacitor to the run/ss pin soft-start the run/ss pin can be used to soft-start the ltm8021, reducing the maximum input current during start-up. the run/ss pin is driven through an external rc flter to create a voltage ramp at this pin. figure 2 shows the soft-start circuit. by choosing a large rc time constant, the peak start-up current can be reduced to the current that is required to regulate the output, with no overshoot. choose the value of the resistor so that it can supply 80a when the run/ss pin reaches 2v. figure 3. the input diode prevents a shorted input from discharging a backup battery tied to the output. it also protects the circuit from a reversed input. the ltm8021 runs only when the input is present v out v in run/ss bias gnd ltm8021 8021 f03 v out r adj c out rt v in 4v to 36v c in c in v in c out fb gnd v out run/ss r adj bias plane 8021 f04 figure 4. layout showing suggested external components, gnd plane and thermal vias shorted input protection care needs to be taken in systems where the output will be held high when the input to the ltm8021 is absent. this may occur in battery charging applications or in battery backup systems where a battery or some other supply is diode ored with the ltm8021s output. if the v in pin is allowed to foat and the run/ss pin is held high (either by a logic signal or because it is tied to v in ), then the ltm8021s internal circuitry will pull its quiescent current through its internal power switch. this is fne if your system can tolerate a few milliamps in this state. if the run/ss pin is grounded, the internal power switch current will drop to essentially zero. however, if the v in pin is grounded while the output is held high, then parasitic diodes inside the ltm8021 can pull large currents from the output through the internal power switch and the v in pin. figure 3 shows a circuit that will run only when the input voltage is present and that protects against a shorted or reversed input. pcb layout most of the problems associated with the pcb layout have been alleviated or eliminated by the high level of integration of the ltm8021. the ltm8021 is nevertheless a switching power supply, and care must be taken to minimize emi and ensure proper operation. even with the high level of integration, one may fail to achieve a specifed operation with a haphazard or poor layout. see figure 4 for a suggested layout. ensure that the grounding and heatsinking are acceptable. a few rules to keep in mind are: 1. place the c in capacitor as close as possible to the v in and gnd connection of the ltm8021. 2. place the c out capacitor as close as possible to the v out and gnd connection of the ltm8021. 3. place the c in and c out capacitors such that their ground currents fow directly adjacent to, or underneath the ltm8021. 8021 f02 run/ss gnd 0.22f run 15k ltm8021 8021fd
11 for more information www.linear.com/ltm8021 a pplica t ions i n f or m a t ion 4. connect all of the gnd connections to as large a copper pour or plane area as possible on the top layer. avoid breaking the ground connection between the external components and the ltm8021. hot-plugging safely the small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of ltm8021. however, these capacitors can cause problems if the ltm8021 is plugged into a live supply (see the linear technology application note 88 for a complete discussion). the low loss ceramic capacitor combined with stray inductance in series with the power source forms an under damped tank circuit, and the volt - age at the v in pin of the ltm8021 can ring to twice the nominal input voltage, possibly exceeding the ltm8021s rating and damaging the part. if the input supply is poorly controlled or the user will be plugging the ltm8021 into an energized supply, the input network should be designed to prevent this overshoot. figure 5 shows the waveforms that result when an ltm8021 circuit is connected to a 24v supply through six feet of 24-gauge twisted pair. the frst plot is the response with a 2.2f ceramic capacitor at the input. the input voltage rings as high as 35v and the input current peaks at 20a. one method of damping the tank circuit is to add another capacitor with a series resistor to + ltm8021 4.7f v in closing switch simulates hot plug i in (5a) (5b) low impedance energized 24v supply stray inductance due to 6 feet (2 meters) of twisted pair + ltm8021 4.7f 0.1f 0.7 (5c) + ltm8021 4.7f 22f ai.ei. + v in 20v/div i in 10a/div 20s/div danger ringing v in may exceed absolute maximum rating v in 20v/div i in 10a/div 20s/div 8021 f05 v in 20v/div i in 10a/div 20s/div figure 5. ensures reliable operation when the ltm8021 is connected to a live supply ltm8021 8021fd
12 for more information www.linear.com/ltm8021 a pplica t ions i n f or m a t ion the circuit. in figure 5b an aluminum electrolytic capacitor has been added. this capacitors high equivalent series resistance damps the circuit and eliminates the voltage overshoot. the extra capacitor improves low frequency ripple fltering and can slightly improve the effciency of the circuit, though it is likely to be the largest component in the circuit. an alternative solution is shown in figure 5c. a 0.7w resistor is added in series with the input to eliminate the voltage overshoot (it also reduces the peak input current). a 0.1f capacitor improves high frequency fltering. this solution is smaller and less expensive than the electrolytic capacitor. for high input voltages its impact on effciency is minor, reducing effciency less than one-half percent for a 5v output at full load operating from 24v. thermal considerations the ltm8021 output current may need to be derated if it is required to operate in a high ambient temperature or deliver a large amount of continuous power. the amount of current derating is dependent upon the input voltage, output power and ambient temperature. the temperature rise curves given in the typical performance charac - teristics section can be used as a guide. these curves were generated by a ltm8021 mounted to a 40.3cm 2 4-layer fr4 printed circuit board. boards of other sizes and layer count can exhibit different thermal behavior, so it is incumbent upon the user to verify proper operation over the intended systems line, load and environmental operating conditions. the thermal resistance numbers listed in page 2 of the data sheet are based on modeling the module package mounted on a test board specifed per jesd51-9 (test boards for area array surface mount package thermal measurements). the thermal coeffcients provided in this page are based on jesd 51-12 (guidelines for reporting and using electronic package thermal information). for increased accuracy and fdelity to the actual application, many designers use fea to predict thermal performance. to that end, page 2 of the data sheet typically gives four thermal coeffcients: ja C thermal resistance from junction to ambient. jcbottom C thermal resistance from junction to the bottom of the product case. jctop C thermal resistance from junction to top of the product case. jb C thermal resistance from junction to the printed circuit board. while the meaning of each of these coeffcients may seem to be intuitive, jedec has defned each to avoid confusion and inconsistency. these defnitions are given in jesd 51-12, and are quoted or paraphrased below: ja is the natural convection junction-to-ambient air thermal resistance measured in a one cubic foot sealed enclosure. this environment is sometimes referred to as still air although natural convection causes the air to move. this value is determined with the part mounted to a jesd 51-9 defned test board, which does not refect an actual application or viable operating condition. jcbottom is the thermal resistance between the junction and bottom of the package with all of the component power dissipation fowing through the bottom of the package. in the typical module converter, the bulk of the heat fows out the bottom of the package, but there is always heat fow out into the ambient environment. as a result, this thermal resistance value may be useful for comparing packages but the test conditions dont generally match the users application. jctop is determined with nearly all of the component power dissipation fowing through the top of the package. as the electrical connections of the typical module converter are on the bottom of the package, it is rare for an application to operate such that most of the heat fows from the junc - tion to the top of the part. as in the case of jcbottom , this value may be useful for comparing packages but the test conditions dont generally match the users application. ltm8021 8021fd
13 for more information www.linear.com/ltm8021 a pplica t ions i n f or m a t ion jb is the junction-to-board thermal resistance where almost all of the heat fows through the bottom of the module converter and into the board, and is really the sum of the jcbottom and the thermal resistance of the bottom of the part through the solder joints and through a portion of the board. the board temperature is measured a specifed distance from the package, using a two sided, two layer board. this board is described in jesd 51-9. given these defnitions, it should now be apparent that none of these thermal coeffcients refects an actual physical operating condition of a module converter. thus, none of them can be individually used to accurately predict the thermal performance of the product. likewise, it would be inappropriate to attempt to use any one coeffcient to correlate to the junction temperature vs load graphs given in the products data sheet. the only appropriate way to use the coeffcients is when running a detailed thermal analysis, such as fea, which considers all of the thermal resistances simultaneously. a graphical representation of these thermal resistances is given in figure 6. the blue resistances are contained within the module converter, and the green are outside. the die temperature of the ltm8021 must be lower than the maximum rating of 125c, so care should be taken in the layout of the circuit to ensure good heat sinking of the ltm8021. the bulk of the heat fow out of the ltm8021 is through the bottom of the module converter and the lga pads into the printed circuit board. consequently a poor printed circuit board design can cause excessive heating, resulting in impaired performance or reliability. please refer to the pcb layout section for printed circuit board design suggestions. 8021 f06 module device junction-to-case (top) resistance junction-to-board resistance junction-to-ambient resistance (jesd 51-9 defined board) case (top)-to-ambient resistance board-to-ambient resistance junction-to-case (bottom) resistance junction ambient case (bottom)-to-board resistance figure 6. thermal model of module regulator ltm8021 8021fd
14 for more information www.linear.com/ltm8021 t ypical a pplica t ions 0.8v step-down converter ltm8021 8021 ta02 v in * 3.4v to 36v 5v v out 0.8v at 500ma 1f 100f run/ss v in bias v out gnd adj *running voltage range. please refer to the applications information section for start-up details. 1.8v step-down converter 5v step-down converter ltm8021 8021 ta04 v in * 7v to 36v v out 5v at 500ma 1f *running voltage range. please refer to the applications information section for start-up details. 2.2f 19.1k run/ss bias gnd adj v in v out ltm8021 8021 ta03 v in * 3.4v to 36v v out 1.8v at 500ma 1f 100f 78.7k run/ss bias gnd adj 5v v in v out *running voltage range. please refer to the applications information section for start-up details. C5v positive-to-negative converter load current vs input voltage ltm8021 8021 ta05 v in * 3.75v to 31v 1f ?5v 4.7f optional schottky clamp 19.1k run/ss bias gnd adj v in v out *running voltage range. please refer to the applications information section for start-up details. v in (v) 0 i load (ma) 400 500 300 200 10 20 5 15 25 100 0 600 8021 ta05b ltm8021 8021fd
15 for more information www.linear.com/ltm8021 p ackage descrip t ion please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. 6.250 bsc package top view 11.250 bsc 4 pad 1 corner x y aaa z aaa z 2.72 ? 2.92 detail a package side view detail a substrate mold cap 0.27 ? 0.37 2.40 ? 2.60 bbb z z lga 35 0113 rev b package in tray loading orientation ltmxxxxxx module tray pin 1 bevel component pin ?a1? 4.445 4.445 3.175 3.175 1.905 0.0000 1.905 0.635 0.635 1.270 1.270 0.9525 1.5875 0.635 0.9525 0.3175 2.540 2.540 suggested pcb layout top view 0.0000 lga package 35-lead (11.25mm 6.25mm 2.82mm) (reference ltc dwg # 05-08-1805 rev b) notes: 1. dimensioning and tolerancing per asme y14.5m-1994 2. all dimensions are in millimeters land designation per jesd mo-222, spp-010 and spp-020 5. primary datum -z- is seating plane 6. the total number of pads: 35 4 3 details of pad #1 identifier are optional, but must be located within the zone indicated. the pad #1 identifier may be either a mold or a marked feature symbol aaa bbb tolerance 0.15 0.10 7 package row and column labeling may vary among module products. review each package layout carefully ! pads see notes 1.270 bsc 0.605 ? 0.665 0.605 ? 0.665 8.890 bsc 5.080 bsc pad 1 c (0.30) h b a d c 5 1 3 2 3 4 ef package bottom view g 7 see notes ltm8021 8021fd
16 for more information www.linear.com/ltm8021 p ackage descrip t ion ltm8021 pinout (sorted by pin number) pin signal description a1 run/ss a2 adj a4 v in a5 v in b1 gnd b2 gnd b4 v in b5 v in c1 gnd c2 gnd d1 gnd d2 gnd d3 gnd d4 gnd d5 gnd e1 gnd e2 gnd e3 gnd e4 gnd e5 gnd f1 gnd f2 gnd f3 v out f4 v out f5 v out g1 gnd g2 gnd g3 v out g4 v out g5 v out h1 gnd h2 gnd h3 bias h4 v out h5 v out ltm8021 8021fd
17 for more information www.linear.com/ltm8021 information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. rev date description page number d 3/14 updated thermal resistance values updated order information table updated thermal considerations section 2 2 12, 13 r evision h is t ory (revision history begins at rev d) ltm8021 8021fd
18 for more information www.linear.com/ltm8021 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 ? linear technology corporation 2008 lt 0314 rev d ? printed in usa (408) 432-1900 fax : (408) 434-0507 www.linear.com/ltm8021 r ela t e d p ar t s p ackage p ho t o part number description comments ltm4600 10a dc/dc module basic 10a dc/dc module, 15mm 15mm 2.8mm lga ltm4600hvmpv military plastic 10a dc/dc module C55c to 125c operation, 15mm 15mm 2.8mm lga ltm4601/ ltm4601a 12a dc/dc module with pll, output tracking/margining and remote sensing synchronizable, polyphase ? operation, ltm4601-1 version has no remote sensing ltm4602 6a dc/dc module pin-compatible with the ltm4600 ltm4603 6a dc/dc module with pll and output tracking/ margining and remote sensing synchronizable, polyphase operation, ltm4603-1 version has no remote sensing, pin-compatible with the ltm4601 ltm4604 4a low v in dc/dc module 2.375v v in 5v, 0.8v v out 5v, 9mm 15mm 2.3mm lga ltm4605 5a to 12a buck-boost module high effciency, adjustable frequency, 4.5v v in 20v, 0.8v v out 16v, 15mm 15mm 2.8mm ltm4607 5a to 12a buck-boost module high effciency, adjustable frequency, 4.5v v in 36v, 0.8v v out 25v, 15mm 15mm 2.8mm ltm4608 8a low v in dc/dc module 2.375v v in 5v, 0.8v v out 5v, 9mm 15mm 2.8mm lga ltm8020 36v, 200ma dc/dc module 4v v in 36v, 1.25v v out 5v, 6.25mm 6.25mm 2.3mm lga ltm8022 1a, 36v dc/dc module adjustable frequency, 0.8v v out 5v, 11.25mm 9mm 2.82mm, pin-compatible to the ltm8023 ltm8023 2a, 36v dc/dc module adjustable frequency, 0.8v v out 5v, 11.25mm 9mm 2.82mm, pin-compatible to the ltm8022 3.3v step-down converter t ypical a pplica t ion ltm8021 8021 ta06 v in * 5.5v to 36v v out 3.3v at 500ma 1f 4.7f 32.4k run/ss bias gnd adj v in v out *running voltage range. please refer to the applications information section for start-up details. ltm8021 8021fd

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