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1 for more information www.linear.com/ltm8068 typical application features description 2.8v in to 40v in isolated module dc/dc converter with ldo post regulator the lt m ? 8068 is a 2kvac isolated flyback module ? (power module) dc/dc converter with ldo post regula - tor. included in the package are the switching controller, power switches, transformer , ldo, and all support com - ponents. operating over an input voltage range of 2.8v to 40v, the ltm8068 supports an output voltage range of 2.5v to 18v , set by a single resistor. there is also a linear post regulator whose output voltage is adjustable from 1.2v to 18v as set by a single resistor. only output and input capacitors are needed to finish the design. the ltm8068 is packaged in a thermally enhanced, com - pact ( 9mm 11.25mm 4.92mm ) overmolded ball grid array (bga) package suitable for automated assembly by standard surface mount equipment. the ltm8068 is available with snpb or rohs compliant terminal finish. l , lt, ltc, ltm, linear technology, the linear logo and module are registered trademarks of analog devices, inc. all other trademarks are the property of their respective owners. applications n 2kvac isolated module converter n ul60950 recognized file e464570 n wide input voltage range: 2.8v to 40v n v out1 output: n up to 450ma (v in ?=?24v , v out1 ?=?5v) n 2.5v to 18v output range n v out2 low noise linear post regulator: n up to 300ma n 1.2v to 18v output range n current mode control n user configurable undervoltage lockout n low profile (9mm 11.25mm 4.92mm) bga package n industrial sensors n industrial switches n ground loop mitigation total output current vs v in 2kvac isolated low noise module regulator v out2 fb2 v outn ltm8068 162k 8068 ta01a (5.6v) v out2 5v 300ma max 10f v out1 v in run gnd fb1 pin byp is not used in this schematic 7.32k 2.2f v in 2.8v to 38v low noise ldo ? ? 22f ltm8068 8068fb 250 350 load current (ma) 8068 ta01 v in (v) 0 9 18 27 36 50 150
2 for more information www.linear.com/ltm8068 pin configuration absolute maximum ratings v in , run .................................................................. 42v v out1 relative to v outn ............................................ 25v v in + v out1 (note 2) ................................................. 4 5v v out2 relative to v outn .......................................... + 20v f b2 relative to v outn ............................................... + 7v gn d to v outn isolation (note 3) ........................... 2 kvac maximum internal temperature (note 4) .............. 12 5 c maximum peak body reflow temperature ........... 24 5 c storage temperature .............................. C 55 c to 125 c (note 1) top view h g f e d c b a 1 2 3 4 5 6 7 bank 2 v outn bank 1 v out1 bank 4 gnd run fb2 byp fb1 bank 5 v in bank 3 v out2 bga package 38-lead (11.25mm 9mm 4.92mm) t jmax = 125c, t ja = 18.2c/w, t jcbottom = 4.8c/w, t jctop = 18.1c/w, t jb = 4.8c/w weight = 1.1g, t values determined per jedec 51-9, 51-12 part number pad or ball finish part marking* package type msl rating temperature range (note 4) device finish code ltm8068ey#pbf sac305 (rohs) ltm8068y e1 bga 3 C40c to 125c ltm8068iy#pbf sac305 (rohs) ltm8068y e1 bga 3 C40c to 125c ltm8068iy snpb (63/37) ltm8068y e0 bga 3 C40c to 125c consult marketing for parts specified with wider operating temperature ranges. *device temperature grade is indicated by a label on the shipping container. pad or ball finish 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 order information http://www.linear.com/product/ltm8068#orderinfo ltm8068 8068fb
3 for more information www.linear.com/ltm8068 electrical characteristics 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: v in + v out1 is defined as the sum of: (v in C gnd) + (v out1 C v outn ) note 3: the ltm8068 isolation test voltage of either 2kvac or its equivalent of 2.83kvdc is applied for one second. the l denotes the specifications which apply over the full internal operating temperature range, otherwise specifications are at t a = 25c, run = 2v (note 4). parameter conditions min typ max units minimum input dc voltage run = 2v l 2.8 v v out1 dc voltage r fb1 = 15.4k r fb1 = 8.25k r fb1 = 2.37k l 4.75 2.5 5 18 5.25 v v v v in quiescent current v run = 0v not switching 7 3 a ma v out1 line regulation 3v v in 40v, i out = 0.1a, run = 2v 1 % v out1 load regulation 0.05a i out 0.3a, run = 2v 1 % v out1 ripple (rms) i out = 0.1a, 1mhz bw 30 mv isolation voltage (note 3) 2 kv input short-circuit current v out1 shorted 80 ma run pin input threshold run pin falling 1.18 1.214 1.25 v run pin current v run = 1v v run = 1.3v 2.5 0.1 a a ldo (v out2 ) minimum input dc voltage (note 5) 1.5 2.3 v v out2 voltage range v out1 = 16v, r fb2 open, no load (note 5) v out1 = 16v, r fb2 = 41.2k, no load (note 5) 1.22 17.7 v v fb2 pin v oltage v out1 = 2v, i out2 = 1ma (note 5) v out1 = 2v, i out2 = 1ma (note 5) l 1.19 1.22 1.25 v v v out2 line regulation 2v < v out1 < 16v, i out2 = 1ma (note 5) 1 5 mv v out2 load regulation v out1 = 5v, 10ma i out2 300ma (note 5) 2 10 mv ldo dropout voltage i out2 = 10ma (note 5) i out2 = 100ma (note 5) i out2 = 300ma (note 5) 0.25 0.34 0.43 v v v v out2 ripple (rms) c byp = 0.01f, i out2 = 300ma, bw = 100hz to 100khz (note 5) 20 v rms note 4: the ltm8068e is guaranteed to meet performance specifications from 0c to 125c. specifications over the C40c to 125c internal temperature range are assured by design, characterization and correlation with statistical process controls. ltm8068i is guaranteed to meet specifications over the full C40c to 125c internal operating temperature range. note that the maximum internal temperature is determined by specific operating conditions in conjunction with board layout, the rated package thermal resistance and other environmental factors. note 5: v run = 0v (flyback not running), but the v out2 post regulator is powered by applying a voltage to v out1 . ltm8068 8068fb
4 for more information www.linear.com/ltm8068 typical performance characteristics efficiency vs load current, v out1 ?=?2.5v efficiency vs load current, v out1 ?=?8v input current vs load current, v out1 ?=?2.5 efficiency vs load current, v out1 ?=?3.3v efficiency vs load current, v out1 ?=?12v input current vs load current, v out1 ?=?3.3v efficiency vs load current, v out1 ?=?5v input current vs load current, v out1 ?=?15v input current vs load current, v out1 ?=?5v unless otherwise noted, operating conditions are as in t able 1 (t a ?=?25c). v in = 5v v in = 12v v in = 24v v in = 36v v in = 5v v in = 12v v in = 24v v in = 36v v in = 5v v in = 12v v in = 24v v in = 36v v in = 5v v in = 12v v in = 24v v in = 36v v in = 5v v in = 12v v in = 24v v in = 36v v in = 5v v in = 12v v in = 24v v in = 5v v in = 12v v in = 24v v in = 36v v in = 5v v in = 12v v in = 24v v in = 36v v in = 5v v in = 12v v in = 24v v in = 36v ltm8068 8068fb 350 50 100 150 200 250 300 350 0 25 50 30 75 100 input current (ma) 8068 g07 load current (ma) 0 100 200 300 400 40 0 25 50 75 100 125 input current (ma) 8068 g08 load current (ma) 0 50 100 200 300 400 500 600 0 60 120 180 60 240 300 input current (ma) 8068 g09 70 80 efficiency (%) 8068 g01 load current (ma) load current (ma) 0 50 100 150 200 250 300 350 400 40 0 50 60 70 80 efficiency (%) 8068 g02 load current (ma) 0 100 200 50 300 400 500 600 40 50 60 70 80 90 100 efficiency (%) 8068 g03 load current (ma) 0 100 200 300 400 500 45 150 55 65 75 85 efficiency (%) 8068 g04 load current (ma) 0 50 100 200 150 200 250 300 45 55 65 75 85 efficiency (%) 250 8068 g05 load current (ma) 0 50 100 150 200 250 55 65 300 75 85 efficiency (%) 8068 g06 v in =5v v in =12v v in =24v v in =36v load current (ma) 0
5 for more information www.linear.com/ltm8068 typical performance characteristics input current vs load current, v out1 ?=?8v input current vs load current, v out1 ?=? 12v input current vs v in , v out1 shorted, v out2 open maximum load current vs v in maximum load current vs v in maximum load current vs v in input current vs v in , v out2 shorted maximum load current vs v out1 input current vs load current, v out1 ?=? 15v unless otherwise noted, operating conditions are as in t able 1 (t a ?=?25c). v in = 5v v in = 12v v in = 24v v in = 36v v in = 5v v in = 12v v in = 24v v in = 36v v in = 5v v in = 12v v in = 24v v in = 5v v in = 12v v in = 24v ltm8068 8068fb 100 8v out1 v in (v) 0 10 20 30 40 0 200 400 200 600 8068 g17 maximum load current (ma) 12v out1 15v out1 v in (v) 0 10 20 30 300 40 0 100 200 300 maximum load current (ma) 8068 g18 400 input current (ma) 8068 g10 load current (ma) 0 100 200 load current (ma) 300 0 100 200 300 400 input current (ma) 8068 g11 load current (ma) 0 0 100 200 300 0 100 200 300 400 input current (ma) 8068 g12 100 v in (v) 0 10 20 30 40 0 50 100 150 200 200 250 input current (ma) 8068 g13 v in (v) 0 10 20 30 40 300 0 90 180 270 360 450 input current (ma) 8068 g14 v in =5v v in =12v 400 v in =24v v out1 (v) 0 5 10 15 20 25 0 125 500 250 375 500 maximum load current (ma) 8068 g15 2.5v out1 3.3v out1 v in (v) 0 10 0 20 30 40 100 200 300 400 8068 g16 maximum load current (ma) 5v out1
6 for more information www.linear.com/ltm8068 minimum load current vs v out1 over full input voltage range typical performance characteristics output noise and ripple dc2358a, 200ma load current frequency vs v out1 load current stock dc2358a demo board v out2 dropout unless otherwise noted, operating conditions are as in t able 1 (t a = 25c). v in = 5v v in = 12v v in = 24v v out2 load current (ma) v out2 dropout voltage (v) 0.7 0.6 0.5 0.4 0.3 0.2 0 0.1 8058 g22 0 100 300 200 250 150 50 ?40c 125c 25c v out2 = 3.3v derating, 1.2v out2 derating, 1.5v out2 derating, 2.5v out2 derating,3.3v out2 derating, 1.8v out2 v in = 5v v in = 12v v in = 24v, 36v v in = 5v v in = 12v v in = 24v, 36v v in = 5v v in = 12v v in = 24v, 36v v in = 5v v in = 12v v in = 24v, 36v v in = 5v v in = 12v v in = 24v, 36v ltm8068 8068fb 10 0 100 200 300 400 maximum load current (ma) 8068 g27 15 20 25 minimum load current (ma) 8068 g19 c9 = 470pf hp461 150mhz amplifier at 40db gain 2s/div v out2 500v/div v out1 (v) v out1 20mv/div 8068 g20 load current (ma) 0 100 200 300 400 500 0 600 150 250 350 450 switching frequency (khz) 8068 g21 0lfm airflow ambient temperature ( c) 25 6 50 75 100 125 0 100 200 300 400 maximum load current (ma) 12 8068 g23 0lfm airflow ambient temperature ( c) 25 50 75 100 125 0 100 18 200 300 400 maximum load current (ma) 8068 g24 0lfm airflow ambient temperature ( c) 25 50 75 24 100 125 0 100 200 300 400 maximum load current (ma) 8068 g25 0lfm airflow 0 ambient temperature ( c) 25 50 75 100 125 0 100 200 300 5 400 maximum load current (ma) 8068 g26 0lfm airflow ambient temperature ( c) 25 50 75 100 125
7 for more information www.linear.com/ltm8068 typical performance characteristics unless otherwise noted, operating conditions are as in t able 1 (t a = 25c). derating, 5v out2 derating, 15v out2 derating, 8v out2 derating, 18v out2 derating, 12v out2 v in = 5v v in = 12v, 24v, 36v v in = 5v v in = 12v v in = 24v, 36v v in = 5v v in = 12v v in = 24v, 32v v in = 5v v in = 12v v in = 24v v in = 5v v in = 12v v in = 24v ltm8068 8068fb 100 200 300 400 maximum load current (ma) 8068 g28 0lfm airflow ambient temperature ( c) 25 50 0lfm airflow 75 100 125 0 100 200 300 400 maximum load current (ma) 8068 g29 ambient temperature ( c) 0lfm airflow ambient temperature ( c) 25 50 75 100 125 0 100 200 25 300 maximum load current (ma) 8068 g30 0lfm airflow ambient temperature ( c) 25 50 75 100 125 50 0 50 100 150 200 250 maximum load current (ma) 8068 g31 0lfm airflow ambient temperature ( c) 75 25 50 75 100 125 0 50 100 150 200 100 maximum load current (ma) 8068 g32 125 0
8 for more information www.linear.com/ltm8068 pin functions v out1 (bank 1): v out1 and v outn comprise the isolated output of the ltm8068 flyback stage. apply an external capacitor between v out1 and v outn . do not allow v outn to exceed v out1 . v outn (bank 2): v outn is the return for both v out1 and v out2 . v out1 and v outn comprise the isolated output of the ltm8068 . in most applications, the bulk of the heat flow out of the ltm8068 is through the gnd and v outn pads, so the printed circuit design has a large impact on the thermal performance of the part. see the pcb layout and thermal considerations sections for more details. apply an external capacitor between v out1 and v outn . v out2 (bank 3): the output of the secondary side linear post regulator. apply the load and output capacitor between v out2 and v outn . see the applications information sec - tion for more information on output capacitance and reverse output characteristics. gnd (bank 4): this is the local ground of the ltm8068 primary. in most applications, the bulk of the heat flow out of the ltm8068 is through the gnd and v outn pads, so the printed circuit design has a large impact on the thermal performance of the part. see the pcb layout and thermal considerations sections for more details. v in (bank 5): v in supplies current to the ltm8068 s inter - nal regulator and to the integrated power switch. these pins must be locally bypassed with an external, low esr capacitor. fb2 (pin a2 ): this is the input to the error amplifier of the secondary side ldo post regulator. this pin is internally clamped to 7v. the fb2 pin voltage is 1.22v referenced to v outn and the output voltage range is 1.22v to 12v. apply a resistor from this pin to v outn , using the equation r fb2 = 608.78/(v out2 C 1.22)k?. if the post regulator is not used, leave this pin floating. byp (pin b2): the byp pin is used to bypass the refer - ence of the ldo to achieve low noise performance from the linear post regulator. the byp pin is clamped internally to 0.6v relative to v outn . a small capacitor from v out2 to this pin will bypass the reference to lower the output voltage noise. a maximum value of 0.01f can be used for reducing output voltage noise to a typical 20v rms over a 100hz to 100khz bandwidth. if not used, this pin must be left unconnected. run (pin f3 ): a resistive divider connected to v in and this pin programs the minimum voltage at which the ltm8068 will operate. below 1.24v, the ltm8068 does not deliver power to the secondary. when run is less than 1.24v, the pin draws 2.5a , allowing for a programmable hys - teresis. do not allow a negative voltage (relative to gnd) on this pin. fb1 (pin g7): apply a resistor from this pin to gnd to set the output voltage v out1 relative to v outn , using the recommended value given in table 1. if table 1 does not list the desired v out1 value, the equation r fb1 = 37.415 v out1 C0.955 ( ) k ? may be used to approximate the value. to the seasoned designer, this exponential equation may seem unusual. the equation is exponential due to nonlinear current sources that are used to temperature compensate the regulation. do not drive this pin. ltm8068 8068fb
9 for more information www.linear.com/ltm8068 block diagram v in run fb1 gnd 0.1f 0.1f 499k v out2 v out1 fb2 current mode controller low noise ldo v outn byp 8068 bd ltm8068 8068fb
10 for more information www.linear.com/ltm8068 operation the ltm8068 is a stand-alone isolated flyback switching dc/dc power supply that can deliver up to 450ma of output current at 5v out1 , 24v in . this module provides a regulated output voltage programmable via one external resistor from 2.5v to 18v. it is also equipped with a high performance linear post regulator. the input voltage range of the ltm8068 is 2.8v to 40v. given that the ltm8068 is a flyback converter, the output current depends upon the input and output voltages, so make sure that the input voltage is high enough to support the desired out - put voltage and load current. the typical performance characteristics section gives several graphs of the maxi - mum load versus v in for several output voltages. a simplified block diagram is given. the ltm8068 con - tains a current mode controller, power switching ele - ment, power transformer, power schottky diode, a mod - est amount of input and output capacitance, and a high per formance linear post regulator . the ltm8068 has a galvanic primary to secondary iso - lation rating of 2kvac . for details please refer to the isolation, working voltage and safely compliance sec - tion. the ltm8068 is a ul 60950 recognized component. the run pin is used to turn on or off the ltm8068, dis - connecting the output and reducing the input current to 1a or less. the ltm8068 is a variable frequency device. for a given input and output voltage, the frequency decreases as the load increases. for light loads, the current through the internal transformer may be discontinuous. the post regulator is a high performance 300ma low dropout regulator with micropower quiescent current and shutdown. the device is capable of supplying 300ma at a dropout voltage of 430mv. output voltage noise can be lowered to 20v rms over a 100hz to 100khz bandwidth with the addition of a 0.01f reference bypass capacitor. additionally, this reference bypass capacitor will improve transient response of the regulator, lowering the settling time for transient load conditions. the linear regulator is protected against both reverse input and reverse output voltages. ltm8068 8068fb
11 for more information www.linear.com/ltm8068 applications information for most applications, the design process is straight for - ward, summarized as follows: 1. look at table 1a (or table 1b, if the post linear regula - tor is used) and find the row that has the desired input range and output voltage. 2. apply the recommended c in , c out1 , c out2 , r fb1 and r fb2 as required. while these component combinations have been tested for proper operation, it is incumbent upon the user to verify proper operation over the intended systems line, load and environmental conditions. bear in mind that the maximum output current may be limited by junc - tion temperature, the relationship between the input and output voltage magnitude and polarity and other factors. please refer to the graphs in the typical performance characteristics section for guidance. capacitor selection considerations the c in , c out1 and c out2 capacitor values in table 1 are the minimum recommended values for the associated operating 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, if it is necessary. again, it is incumbent upon the user to verify proper operation over the intended sys - tems 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 applied voltage and give dependable service. other types, includ - ing y5v and z5u have very large temperature and voltage coefficients of capacitance. in an application circuit they may have only a small fraction of their nominal capaci - tance resulting in much higher output voltage ripple than expected. a final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the ltm8068 . a ceramic input capacitor combined with trace or cable inductance forms a high-q (underdamped) tank circuit. if the ltm8068 circuit is plugged into a live supply, the input voltage can ring to much higher than its nominal value, possibly exceeding the devices rating. this situa - tion is easily avoided; see the hot-plugging safely section. ltm8068 table 1a. recommended component values and configuration for specific v out1 voltages (t a = 25c) v in v out1 c in c out1 r fb1 2.8v to 40v 2.5v 2.2f, 50v, 1206 100f, 6.3v, 1210 15.4k 2.8v to 40v 3.3v 2.2f, 50v, 1206 47f, 6.3v, 1210 11.8k 2.8v to 40v 5v 2.2f, 50v, 1206 22f, 16v, 1210 8.25k 2.8v to 37v 8v 2.2f, 50v, 1206 22f, 16v, 1210 5.23k 2.8v to 33v 12v 4.7f, 50v, 1206 10f, 50v, 1210 3.48k 2.8v to 30v 15v 4.7f, 50v, 1206 4.7f, 25v, 1210 2.8k 2.8v to 27v 18v 4.7f, 50v, 1206 4.7f, 25v, 1210 2.37k note: an input bulk capacitor is required. ltm8068 8068fb
12 for more information www.linear.com/ltm8068 ltm8068 table 1b. recommended component values and configuration for specific v out2 voltages (t a = 25c) v in v out1 v out2 c in c out1 c out2 r fb1 r fb2 2.8v to 40v 1.7v 1.2v 2.2f, 50v, 1206 100f, 6.3v, 1210 10f, 6.3v, 1206 20.5k open 2.8v to 40v 2v 1.5v 2.2f, 50v, 1206 100f, 6.3v, 1210 10f, 6.3v, 1206 18.2k 2.32m 2.8v to 40v 2.4v 1.8v 2.2f, 50v, 1206 100f, 6.3v, 1210 10f, 6.3v, 1206 15.8k 1.07m 2.8v to 40v 3.1v 2.5v 2.2f, 50v, 1206 100f, 6.3v, 1210 10f, 6.3v, 1206 12.7k 487k 2.8v to 40v 3.9v 3.3v 2.2f, 50v, 1206 47f, 6.3v, 1210 10f, 6.3v, 1206 10.5k 294k 2.8v to 38v 5.6v 5v 2.2f, 50v, 1206 22f, 16v, 1210 10f, 6.3v, 1206 7.32k 162k 2.8v to 36v 8.6v 8v 2.2f, 50v, 1206 22f, 16v, 1210 10f, 10v, 1206 4.89k 88.7k 2.8v to 32v 12.7v 12v 4.7f, 50v, 1206 10f, 50v, 1210 22f, 16v, 1206 3.32k 56.2k 2.8v to 29v 15.8v 15v 4.7f, 50v, 1206 4.7f, 25v, 1210 22f, 16v, 1206 2.67k 44.2k 2.8v to 26v 18.8v 18v 4.7f, 50v, 1206 4.7f, 25v, 1210 22f, 25v, 1206 2.26k 36.5k note: an input bulk capacitor is required. applications information isolation, working voltage and safety compliance the ltm8068 isolation is 100% hi-pot tested by tying all of the primary pins together, all of the secondary pins together and subjecting the two resultant circuits to a high voltage differential for one second. this establishes the isolation voltage rating of the ltm8068 component. the isolation rating of the ltm8068 is not the same as the working or operational voltage that the application will experience. this is subject to the applications power source, operating conditions, the industry where the end product is used and other factors that dictate design requirements such as the gap between copper planes, traces and component pins on the printed circuit board, as well as the type of connector that may be used. to maxi - mize the allowable working voltage, the ltm8068 has two columns of solder balls removed to facilitate the printed circuit board design. the ball to ball pitch is 1.27mm , and the typical ball diameter is 0.78mm. accounting for the missing columns and the ball diameter, the printed circuit board may be designed for a metal-to-metal separation of up to 3.03mm . this may have to be reduced somewhat to allow for tolerances in solder mask or other printed circuit board design rules. for those situations where informa- tion about the spacing of ltm8068 internal circuitry is required, the minimum metal to metal separation of the primary and secondary is 0.75mm. to reiterate, the manufacturer s isolation voltage rating and the required working or operational voltage are often different numbers. in the case of the ltm8068, the iso - lation voltage rating is established by 100% hi-pot test - ing. the working or operational voltage is a function of the end product and its system level specifications. the actual required operational voltage is often smaller than the manufacturers isolation rating. the ltm8068 is a ul recognized component under ul 60950, file number e464570. the ul 60950 insula - tion category of the ltm8068 transformer is functional. considering ul 60950 table 2n and the gap distances stated above, 3.03mm external and 0.75mm internal, the ltm8068 may be operated with up to 250v working voltage in a pollution degree 2 environment. the actual working voltage, insulation category, pollution degree and other critical parameters for the specific end application depend upon the actual environmental, application and safety compliance requirements. it is therefore up to the user to perform a safety and compliance review to ensure that the ltm8068 is suitable for the intended application. v out2 post regulator v out2 is produced by a high performance low dropout 300ma regulator. at full load, its dropout is less than 430mv . its output is set by applying a resistor from the r fb2 pin to gnd; the value of r fb2 can be calculated by the equation: r fb2 = 608.78 v out2 C 1.22 k ? ltm8068 8068fb
13 for more information www.linear.com/ltm8068 applications information v out2 post regulator bypass capacitance and low noise performance the v out2 linear regulator may be used with the addition of a 0.01f bypass capacitor from v out to the byp pin to lower output voltage noise. a good quality low leak - age capacitor, such as a x5r or x7r ceramic, is recom - mended. this capacitor will bypass the reference of the regulator , lowering the output voltage noise to as low as 20v rms . using a bypass capacitor has the added benefit of improving transient response. safety rated capacitors some applications require safety rated capacitors, which are high voltage capacitors that are specifically designed and rated for ac operation and high voltage surges. these capacitors are often certified to safety standards such as ul 60950, iec 60950 and others. in the case of the ltm8068, a common application of a safety rated capaci - tor would be to connect it from gnd to v outn . to provide maximum flexibility, the ltm8068 does not include any components between gnd and v outn . any safety capaci - tors must be added externally. the specific capacitor and circuit configuration for any application depends upon the safety requirements of the system into which the ltm8068 is being designed. table 2 provides a list of possible capacitors and their manufac - turers. the application of a capacitor from gnd to v outn may also reduce the high frequency output noise on the output. table 2. safety rated capacitors manufacturer part number description murata electronics ga343dr7gd472kw01l 4700pf, 250v ac,?x7r, 4.5mm 3.2mm capacitor johanson dielectrics 302r29w471kv3e-****-sc 470pf, 250v ac,?x7r, 4.5mm 2mm capacitor syfer technology 1808ja250102jctsp 100pf, 250v ac, c0g, 1808 capacitor pcb layout most of the headaches associated with pcb layout have been alleviated or even eliminated by the high level of integration of the ltm8068. the ltm8068 is neverthe - less a switching power supply, and care must be taken to minimize electrical noise to ensure proper operation. even with the high level of integration, you may fail to achieve specified operation with a haphazard or poor layout. see figure?1 for a suggested layout. ensure that the grounding and heat sinking are acceptable. a few rules to keep in mind are: 1. place the r fb1 and r fb2 resistors as close as possible to their respective pins. 2. place the c in capacitor as close as possible to the v in and gnd connections of the ltm8068. 3. place the c out1 capacitor as close as possible to v out1 and v outn . likewise, place the c out2 capaci- tor as close as possible to v out2 and v outn . 4. place the c in and c out capacitors such that their ground current flow directly adjacent or underneath the ltm8068. 8068 f01 run fb2 byp fb1 ltm8058 c out2 c out1 v outn v out2 v in v out1 c in thermal/interconnect vias figure?1. layout showing suggested external components, planes and thermal vias ltm8068 8068fb
14 for more information www.linear.com/ltm8068 applications information 5. connect all of the gnd connections to as large a cop - per pour or plane area as possible on the top layer. avoid breaking the ground connection between the external components and the ltm8068. 6. use vias to connect the gnd copper area to the board s internal ground planes. liberally distribute these gnd vias to provide both a good ground connection and thermal path to the internal planes of the printed circuit board. pay attention to the location and density of the thermal vias in figure?1. the ltm8068 can benefit from the heat sinking afforded by vias that connect to internal gnd planes at these locations, due to their proximity to internal power handling components. the optimum number of thermal vias depends upon the printed circuit board design. for example, a board might use very small via holes. it should employ more thermal vias than a board that uses larger holes. minimum load due to the nature of the flyback regulator in general, and the ltm8068 control scheme specifically, the ltm8068 requires a minimum load for proper operation. otherwise, the output may go out of regulation if the load is too light. the most common way to address this is to place a resistor across the output. the minimum load current vs v out over full output voltage range graph in the typical performance characteristics section of may be used as a guide in selecting the resistor. note that this graph describes room temperature operation. if the end appli - cation operates at a colder temperature, the minimum load requirement may be higher and the minimum load condition must be characterized for the lowest operating temperature. if it is impractical to place a resistive load permanently across the output, a resistor and zener diode may be used instead, as shown in figure 2. while the minimum load resistor mentioned in the prior paragraph will always draw current while the ltm8068 output is powered, the series resistor-zener diode combination will only draw current if the output is too high. when using this circuit, take care to ensure that the characteristics of the zener diode are appropriate for the intended applications tem - perature range. figure 2: use a resistor and zener diode to meet the minimum load requirement hot-plugging safely the small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of the ltm8068 . however, these capaci - tors can cause problems if the ltm8068 is plugged into a live supply (see linear t echnology application note 88 for a complete discussion). the low loss ceramic capacitor combined with stray inductance in series with the power source forms an underdamped tank circuit, and the volt - age at the v in pin of the ltm8068 can ring to more than twice the nominal input voltage, possibly exceeding the ltm8068 s rating and damaging the part. if the input supply is poorly controlled or the user will be plugging the ltm8068 into an energized supply, the input network should be designed to prevent this overshoot. this can be accomplished by installing a small resistor in series to v in , but the most popular method of controlling input voltage overshoot is adding an electrolytic bulk capacitor to the v in net. this capacitor s relatively high equivalent series resistance damps the circuit and eliminates the voltage overshoot. the extra capacitor improves low frequency ripple filtering and can slightly improve the efficiency of the circuit, though it can be a large component in the circuit. thermal considerations the ltm8068 output current may need to be derated if it is required to operate in a high ambient temperature. 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 characteristics section can be used as a guide. these curves were generated by the ltm8068 mounted to a 58c m 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 ltm8068 8068fb ltm8068 v outp v outn 8068 f02
15 for more information www.linear.com/ltm8068 applications information operation over the intended systems line, load and envi- ronmental operating conditions. for increased accuracy and fidelity to the actual applica - tion, many designers use fea to predict thermal perfor - mance. to that end, the pin configuration section of the data sheet typically gives four thermal coefficients : ja : thermal resistance from junction to ambient jcbottom : thermal resistance from junction to the bottom of the product case jctop : thermal resistance from junction to top of the product case jcboard : thermal resistance from junction to the printed circuit board. while the meaning of each of these coefficients may seem to be intuitive, jedec has defined each to avoid confu - sion and inconsistency. these definitions are given in jesd 51-12, and are quoted or paraphrased as follows: 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 defined test board, which does not reflect an actual application or viable operating condition. jcbottom is the junction-to-board thermal resistance with all of the component power dissipation flowing through the bottom of the package. in the typical module con - verter, the bulk of the heat flows out the bottom of the package, but there is always heat flow out into the ambient environment. as a result, this thermal resistance value may be useful for comparing packages but the test condi - tions dont generally match the users application. jctop is determined with nearly all of the component power dissipation flowing through the top of the pack - age. 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 flows from the junction to the top of the part. as in the case of jcbottom , this value may be useful for comparing pack - ages but the test conditions don t generally match the users application. jcboard is the junction-to-board thermal resistance where almost all of the heat flows 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 specified distance from the package, using a two-sided, two-layer board. this board is described in jesd 51-9. given these definitions, it should now be apparent that none of these thermal coefficients reflects an actual physi - cal 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 coefficient to correlate to the junction temperature vs load graphs given in the products data sheet. the only appropriate way to use the coefficients 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 3. the blue resistances are contained within the module converter, and the green are outside. the die temperature of the ltm8068 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 ltm8068. the bulk of the heat flow out of the ltm8068 is through the bottom of the module and the bga pads into the printed circuit board. consequently a poor printed circuit board design can cause excessive heating, result - ing in impaired performance or reliability. please refer to the pcb layout section for printed cir cuit board design suggestions. ltm8068 8068fb
16 for more information www.linear.com/ltm8068 typical applications 12v flyback converter with low noise bypass 3.3v flyback converter v out2 maximum load current vs v in v out2 maximum load current vs v in v out2 fb2 v outn ltm8068 294k 8068 ta02a (3.9v) v out2 3.3v 300ma max 10f v out1 v in run gnd fb1 pin byp is not used in this schematic 10.5k 2.2f v in 2.8v to 40v low noise ldo ? ? 47f v out2 fb2 byp v outn ltm8068 56.2k 0.01f 8068 ta03a (12.7v) v out2 12v 240ma max 22f v out1 v in run gnd fb1 3.32k 4.7f v in 2.8v to 32v low noise ldo ? ? 10f figure 3. approximate thermal model of ltm8068 8068 f03 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 applications information ltm8068 8068fb 250 350 load current (ma) 8068 ta02b v in (v) 0 8 16 24 32 v in (v) 50 100 150 200 250 load current (ma) 8068 ta03b 0 10 20 30 40 50 150
17 for more information www.linear.com/ltm8068 pin function pin function pin function pin function pin function pin function pin function pin function a1 v out2 b1 v out2 c1 - d1 - e1 gnd f1 - g1 v in h1 v in a2 fb2 b2 byp c2 - d2 - e2 gnd f2 - g2 v in h2 v in a3 v outn b3 v outn c3 - d3 - e3 gnd f3 run g3 - h3 - a4 v outn b4 v outn c4 - d4 - e4 gnd f4 gnd g4 gnd h4 gnd a5 v outn b5 v outn c5 - d5 - e5 gnd f5 gnd g5 gnd h5 gnd a6 v out1 b6 v out1 c6 - d6 - e6 gnd f6 gnd g6 gnd h6 gnd a7 v out1 b7 v out1 c7 - d7 - e7 gnd f7 gnd g7 fb1 h7 gnd pin assignment table (arranged by pin number) package description package photo ltm8068 8068fb
18 for more information www.linear.com/ltm8068 package description 5. primary datum -z- is seating plane 6. solder ball composition is 96.5% sn/3.0% ag/0.5% cu 7 package row and column labeling may vary among module products. review each package layout carefully ! package top view 4 pin ?a1? corner y x aaa z aaa z detail a package bottom view 3 see notes h g f e d c b a 1234567 pin 1 bga 38 1212 rev a tray pin 1 bevel package in tray loading orientation component pin ?a1? notes: 1. dimensioning and tolerancing per asme y14.5m-1994 2. all dimensions are in millimeters ball designation per jesd ms-028 and jep95 4 3 details of pin #1 identifier are optional, but must be located within the zone indicated. the pin #1 identifier may be either a mold or marked feature detail a ?b (38 places) detail b substrate 0.27 ? 0.37 3.95 ? 4.05 // bbb z a a1 b1 ccc z detail b package side view mold cap z m x yzddd m zeee symbol a a1 a2 b b1 d e e f g aaa bbb ccc ddd eee min 4.72 0.50 4.22 0.60 0.60 nom 4.92 0.60 4.32 0.75 0.63 11.25 9.0 1.27 8.89 7.62 max 5.12 0.70 4.42 0.90 0.66 0.15 0.10 0.20 0.30 0.15 notes dimensions total number of balls: 38 a2 d e e b f g suggested pcb layout top view 0.000 0.635 1.905 0.635 3.175 1.905 4.445 3.175 4.445 3.810 2.540 1.270 3.810 2.540 1.270 0.3175 0.3175 0.000 4.1275 4.7625 ltmxxxxxx module bga package 38-lead (11.25mm 9.00mm 4.92mm) (reference ltc dwg # 05-08-1925 rev a) 7 see notes please refer to http://www.linear.com/product/ltm8068#packaging for the most recent package drawings. ltm8068 8068fb
19 for more information www.linear.com/ltm8068 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 representa - tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. revision history rev date description page number a 05/16 corrected symbol of internal switch on block diagram from npn transistor to n-channel mosfet 9 b 07/17 added minimum load section 14 ltm8068 8068fb
20 for more information www.linear.com/ltm8068 ? linear technology corporation 2016 lt 0717 rev b ? printed in usa www.linear.com/ltm8068 related parts typical application 3.3v, 2.5v dual output converter with low noise bypass maximum load current vs v in v out2 fb2 byp v outn ltm8068 487k 0.01f 8068 ta04a v out2 2.5v 300ma max v out1 3.3v 10f v out1 v in run gnd fb1 11.8k 2.2f v in 2.8v to 40v low noise ldo 100f design resources part number description comments ltm8067 2kvac isolated module converter 2.8v??v in ??40v, 2.5v??v out ??24v, ul60950 recognized ltm8047 725vdc, 1.5w isolated module converter 3.1v??v in ??32v, 2.5v??v out ??12v ltm8048 725vdc, 1.5w isolated module converter with ldo post regulator 3.1v??v in ??32v, 1.2v??v out ??12v; 20v rms output ripple ltm8045 inverting or sepic module dc/dc converter 2.8v??v in ??18v, 2.5v??v out ??15v or C2.5v??v out ??C15v, up to 700ma lt ? 8300 isolated flyback converter with 100v in , 150v/260ma power switch 6v??v in ??100v, no opt-isolator required LT8301 isolated flyback converter with 65v/1.2a power switch 2.7v??v in ??42v, no opt-isolator required lt8302 isolated flyback converter with 65v/3.6a power switch 2.8v??v in ??42v, no opt-isolator required subject description module design and manufacturing resources design: ? selector guides ? demo boards and gerber files ? free simulation tools manufacturing: ? quick start guide ? pcb design, assembly and manufacturing guidelines ? package and board level reliability module regulator products search 1. sort table of products by parameters and download the result as a spread sheet. 2. search using the quick power search parametric table. techclip videos quick videos detailing how to bench test electrical and thermal performance of module products. digital power system management linear technologys family of digital power supply management ics are highly integrated solutions that offer essential functions, including power supply monitoring, supervision, margining and sequencing, and feature eeprom for storing user configurations and fault logging. ltm8068 8068fb 100 200 300 400 load current (ma) 8068 ta04b v out2 v out1 v in (v) 0 8 16 24 32

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