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lt6108-1/lt6108-2 1 610812fa typical application features description high side current sense ampli?er with reference and comparator the lt ? 6108 is a complete high side current sense device that incorporates a precision current sense ampliier, an integrated voltage reference and a comparator. two ver - sions of the lt6108 are available. the lt6108-1 has a latching comparator and the lt6108-2 has a non-latching comparator. in addition, the current sense ampliier and comparator inputs and outputs are directly accessible. the ampliier gain and comparator trip point are conigured by external resistors. the open-drain comparator output allows for easy interface to other system components. the overall propagation delay of the lt6108 is typic ally only 1.4s, allowing for quick reaction to overcurrent condi - tions. the 1mhz bandwidth allows the lt6108 to be used for error detection in critical applications such as motor control. the high threshold accuracy of the comparator, combined with the ability to latch the comparator, ensures the lt6108 can capture high speed events. the lt6108 is fully speciied for operation from C40c to 125c, making it suitable for industrial and automotive applications. the lt6108 is available in the small 8-lead msop and 8-lead dfn packages. circuit fault protection with very fast latching load disconnect applications n current sense ampliier C fast step response: 500ns C low offset voltage: 125v maximum C low gain error: 0.2% maximum n internal 400mv precision reference n internal comparator C fast response time: 500ns C total threshold error: 1.25% maximum C latching or non-latching comparator option n wide supply range: 2.7v to 60v n supply current: 450a n low shutdown current: 5a maximum n speciied for C40c to 125c temperature range n available in 8-lead msop and 8-lead (2mm 3mm) dfn packages n overcurrent and fault detection n current shunt measurement n battery monitoring n motor control n automotive monitoring and control n remote sensing n industrial control l , lt, ltc, ltm, timerblox, linear technology and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. response to overcurrent event sensehi senselo outa lt6108-1 reset inc 250ma disconnect v + en/ rst outc v C 0.1 3.3v 12v 100 10k *cmh25234b 1k 1k 2n2700 6.2v* 6.04k 0.1f irf9640 v out 1.6k 610812 ta01a to load v load 10v/div i load 200ma/div v outc 5v/div 0v0v 0ma 610812 ta01b 5s/div 250ma disconnect downloaded from: http:///
lt6108-1/lt6108-2 2 610812fa absolute maximum ratings total supply voltage (v + to v C ) ................................. 60v maximum voltage (senselo, sensehi, outa) ............................... v + + 1v maximum v + C (senselo or sensehi) .................... 33v maximum en, en/ rst voltage ................................. 60v maximum comparator input voltage ........................ 60v maximum comparator output voltage...................... 60v input current (note 2) .......................................... C10ma sensehi, senselo input current ....................... 10ma differential sensehi or senselo input current .. 2.5ma (note 1) ampli ier output short-circuit duration (to v C ) .. indeinite operating temperature range (note 3) lt6108i ................................................ C40c to 85c lt6108h ............................................ C40c to 125c speciied temperature range (note 3) lt6108i ................................................ C40c to 85c lt6108h ............................................ C40c to 125c maximum junction temperature .......................... 150c storage temperature range .................. C65c to 150c msop lead temperature (soldering, 10 sec) ........ 300c pin configuration lt6108-1 lt6108-2 12 3 4 senselo en/ rst outc v C 87 6 5 sensehiv + outainc top view ms8 package 8-lead plastic msop ja = 163c/w, jc = 45c/w 12 3 4 senselo en outc v C 87 6 5 sensehiv + outainc top view ms8 package 8-lead plastic msop ja = 163c/w, jc = 45c/w top view sensehiv + outainc senselo en/ rst outc v C dcb package 8-lead (2mm 3mm) plastic dfn 9 3 4 2 1 6 5 7 8 ja = 64c/w, jc = 10c/w exposed pad (pin 9) is v C , pcb connection optional top view sensehiv + outainc senselo en outc v C dcb package 8-lead (2mm 3mm) plastic dfn 9 3 4 2 1 6 5 7 8 ja = 64c/w, jc = 10c/w exposed pad (pin 9) is v C , pcb connection optional downloaded from: http:///
lt6108-1/lt6108-2 3 610812fa order information lead free finish tape and reel part marking* package description specified temperature range lt6108aims8-1#pbf lt6108aims8-1#trpbf ltfnd 8-lead plastic msop C40c to 85c lt6108ims8-1#pbf lt6108ims8-1#trpbf ltfnd 8-lead plastic msop C40c to 85c lt6108ahms8-1#pbf lt6108ahms8-1#trpbf ltfnd 8-lead plastic msop C40c to 125c lt6108hms8-1#pbf lt6108hms8-1#trpbf ltfnd 8-lead plastic msop C40c to 125c lt6108aims8-2#pbf lt6108aims8-2#trpbf ltfng 8-lead plastic msop C40c to 85c lt6108ims8-2#pbf lt6108ims8-2#trpbf ltfng 8-lead plastic msop C40c to 85c lt6108ahms8-2#pbf lt6108ahms8-2#trpbf ltfng 8-lead plastic msop C40c to 125c lt6108hms8-2#pbf lt6108hms8-2#trpbf ltfng 8-lead plastic msop C40c to 125c consult l tc marketing for parts speciied with wider operating temperature ranges. *the temperature grade is identiied by a label on the shipping container. consult ltc marketing for information on non-standard lead based inish parts. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel speciications, go to: http://www.linear.com/tapeandreel/ lead free finish tape and reel (mini) tape and reel part marking* package description specified temperature range lt6108idcb-1#trmpbf lt6108idcb-1#trpbf lfnf 8-lead (2mm 3mm) plastic dfn C40c to 85c lt6108hdcb-1#trmpbf lt6108hdcb-1#trpbf lfnf 8-lead (2mm 3mm) plastic dfn C40c to 125c lt6108idcb-2#trmpbf lt6108idcb-2#trpbf lfnh 8-lead (2mm 3mm) plastic dfn C40c to 85c lt6108hdcb-2#trmpbf lt6108hdcb-2#trpbf lfnh 8-lead (2mm 3mm) plastic dfn C40c to 125c trm = 500 pieces. *temperature grades are identiied by a label on the shipping container. consult ltc marketing for parts speciied with wider operating temperature ranges. consult ltc marketing for information on lead based inish parts. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel speciications, go to: http://www.linear.com/tapeandreel/ downloaded from: http:///
lt6108-1/lt6108-2 4 610812fa electrical characteristics the l denotes the speciications which apply over the full operating temperature range, otherwise speciications are at t a = 25c. v + = 12v, v pullup = v + , v en = v en/ rst = 2.7v, r in = 100, r out = r1 + r2 = 10k, gain = 100, r c = 25.5k, c l = c lc = 2pf, unless otherwise noted. (see figure 3) symbol parameter conditions min typ max units v + supply voltage range l 2.7 60 v i s supply current (note 4) v + = 2.7v, r in = 1k, v sense = 5mv 450 a v + = 60v, r in = 1k, v sense = 5mv l 550 650 950 a a supply current in shutdown v + = 2.7v, v en/ rst = 0v, r in = 1k, v sense = 0.5v l 3 5 7 a a v + = 60v, v en/ rst = 0v, r in = 1k, v sense = 0.5v l 7 11 13 a a en/ rst pin current v en/ rst = 0v, v + = 60v (lt6108-1 only) C200 na en pin current v en = 0v, v + = 60v (lt6108-2 only) C100 na v ih en/ rst pin input high v + = 2.7v to 60v (lt6108-1 only) l 1.9 v v il en/ rst pin input low v + = 2.7v to 60v (lt6108-1 only) l 0.8 v v ih en pin input high v + = 2.7v to 60v (lt6108-2 only) l 1.9 v v il en pin input low v + = 2.7v to 60v (lt6108-2 only) l 0.8 v current sense ampliierv os input offset voltage v sense = 5mv, lt6108a v sense = 5mv, lt6108 v sense = 5mv, lt6108a v sense = 5mv, lt6108 l l C125 C350 C250 C450 125 350 250 450 v v v v ? v os / ? t input offset voltage drift v sense = 5mv l 0.8 v/c i b input bias current (senselo, sensehi) v + = 2.7v to 60v l 60 300 350 na na i os input offset current v + = 2.7v to 60v 5 na i outa output current (note 5) l 1 ma psrr power supply rejection ratio (note 6) v + = 2.7v to 60v l 120 114 127 db db cmrr common mode rejection ratio v + = 36v, v sense = 5mv, v icm = 2.7v to 36v 125 db v + = 60v, v sense = 5mv, v icm = 27v to 60v l 110 103 125 db db v sense(max) full-scale input sense voltage (note 5) r in = 500 l 500 mv gain error (note 7) v + = 2.7v to 12v v + = 12v to 60v, v sense = 5mv to 100mv, ms8 package v + = 12v to 60v, v sense = 5mv to 100mv, dfn package l l C0.2 C0.3 C0.08 0 0 % % % senselo voltage (note 8) v + = 2.7v, v sense = 100mv, r out = 2k v + = 60v, v sense = 100mv l l 2.5 27 v v output swing high (v + to v outa ) v + = 2.7v, v sense = 27mv l 0.2 v v + = 12v, v sense = 120mv l 0.5 v bw signal bandwidth i out = 1ma i out = 100a 1 140 mhz khz t r input step response (to 50% of final output voltage) v + = 2.7v, v sense = 24mv step, output rising edge v + = 12v to 60v, v sense = 100mv step, output rising edge 500 500 ns ns t settle settling time to 1% v sense = 10mv to 100mv, r out = 2k 2 s downloaded from: http:///
lt6108-1/lt6108-2 5 610812fa electrical characteristics the l denotes the speciications which apply over the full operating temperature range, otherwise speciications are at t a = 25c. v + = 12v, v pullup = v + , v en = v en/ rst = 2.7v, r in = 100, r out = r1 + r2 = 10k, gain = 100, r c = 25.5k, c l = c lc = 2pf, unless otherwise noted. (see figure 3) symbol parameter conditions min typ max units reference and comparatorv th(r) (note 9) rising input threshold voltage v + = 2.7v to 60v, lt6108a v + = 2.7v to 60v, lt6108 l l 395 392 400 400 405 408 mv mv v hys v hys = v th(r) C v th(f) v + = 2.7v to 60v 3 10 15 mv comparator input bias current v inc = 0v, v + = 60v l C50 na v ol output low voltage i outc = 500a, v + = 2.7v l 60 150 220 mv mv high to low propagation delay 5mv overdrive 100mv overdrive 3 0.5 s s output fall time 0.08 s t reset reset time lt6108-1 only 0.5 s t rpw valid rst pulse width lt6108-1 only l 2 15 s 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: input and output pins have esd diodes connected to ground. the sensehi and senselo pins have additional current handling capability speciied as sensehi, senselo input current. note 3: the lt6108i is guaranteed to meet speciied performance from C40c to 85c. lt6108h is guaranteed to meet speciied performance from C40c to 125c. note 4: supply current is speciied with the comparator output high. when the comparator output goes low the supply current will increase by 75a typically. note 5: the full-scale input sense voltage and the maximum output current must be considered to achieve the speciied performance. note 6: supply voltage and input common mode voltage are varied while ampliier input offset voltage is monitored.note 7: the speciied gain error does not include the effect of external resistors r in and r out . although gain error is only guaranteed between 12v and 60v, similar performance is expected for v + < 12v, as well. note 8: refer to senselo, sensehi range in the applications information section for more information.note 9: the input threshold voltage which causes the output voltage of the comparator to transition from high to low is speciied. the input voltage which causes the comparator output to transition from low to high is the magnitude of the difference between the speciied threshold and the hysteresis. downloaded from: http:///
lt6108-1/lt6108-2 6 610812fa typical performance characteristics input offset voltage vs temperature ampliier offset voltage vs supply voltage offset voltage drift distribution ampliier gain error vs temperature ampliier gain error distribution supply current vs supply voltage start-up supply current enable/disable response performance characteristics taken at t a = 25c, v + = 12v, v pullup = v + , v en = v en/ rst = 2.7v, r in = 100, r out = r1 + r2 = 10k, gain = 100, r c = 25.5k, c l = c lc = 2pf, unless otherwise noted. (see figure 3) supply voltage (v) 0 0 supply current (a) 100 200 300 400 600 10 20 30 40 610812 g01 50 60 500 100s/div v en/ rst 2v/div i s 500a/div 0v 0a 610812 g03 temperature (c) C40 input offset voltage (v) 300200 100 0 C200 C100C300 80 610812 g04 C10 20 50 125 110 65 C25 5 35 95 5 typical units supply voltage (v) 0 C100 offset voltage (v) C60 C20 20 10 20 30 40 610812 g05 50 60 100 C80 C40 0 40 80 60 5 typical units temperature (c) C50 C0.18 gain error (%) C016 C0.12 C0.10 C0.08 0.02 C0.04 0 50 75 610812 g06 C0.14 C0.02 0 C0.06 C25 25 100 125 v sense = 5mv to 100mv r in = 1k r in = 100 0v v + 5v/div 0a i s 500a/div 10s/div 610812 g02 offset voltage drift (v/c) 0 percentage of units (%) 2 4 6 8 12 C1 C1.5 C2 C0.5 0 0.5 1 1.5 2 610812 g38 10 gain error (%) 0 percentage of units (%) 5 15 20 25 v sense = 5mv to 100mv C0.056 C0.068 610812 g07 10 C0.048 C0.052 C0.060 C0.064 ampliier output swing vs temperature temperature (c) C50 0 v + C v outa (v) 0.05 0.15 0.20 0.25 0.50 0.35 0 50 75 610812 g18 0.10 0.40 0.450.30 C25 25 100 125 v + = 12v v sense = 120mv v + = 2.7v v sense = 27mv downloaded from: http:///
lt6108-1/lt6108-2 7 610812fa ampliier input bias current vs temperature ampliier step response (v sense = 0mv to 100mv) ampliier step response (v sense = 0mv to 100mv) ampliier step response (v sense = 10mv to 100mv) ampliier step response (v sense = 10mv to 100mv) ampliier gain vs frequency lt6108-1 step response lt6108-2 step response typical performance characteristics performance characteristics taken at t a = 25c, v + = 12v, v pullup = v + , v en = v en/ rst = 2.7v, r in = 100, r out = r1 + r2 = 10k, gain = 100, r c = 25.5k, c l = c lc = 2pf, unless otherwise noted. (see figure 3) frequency (hz) 22 gain (db) 28 34 40 46 1k 100k 1m 10m 610812 g10 16 10k i outa = 1ma i outa = 100a g = 100, r out = 10k g = 50, r out = 5k g = 20, r out = 2k 0v v sense 100mv/div v outa 1v/div v outc 2v/div v en/ rst 5v/div 0v0v 0v 610812 g11 2s/div r out = 2k 100mv inc overdrive 0v v sense 100mv/div v outa 1v/div v outc 2v/div 0v0v 610812 g12 2s/div r out = 2k,100mv inc overdrive temperature (c) ?25 input bias current (na) 60 80 100 95 610812 g13 4020 50 70 9030 10 0 5 35 65 ?10 ?40 110 20 50 80 125 sensehi senselo v outa 2v/div v sense 50mv/div 0v0v 610812 g14 2s/div r in = 100 g = 100v/v v outa 2v/div v sense 50mv/div 0v0v 610812 g15 2s/div r in = 100 g = 100v/v 0v0v v outa 1v/div v sense 100mv/div 610812 g16 2s/div r in = 1k r out = 20k g = 20v/v 0v0v v outa 1v/div v sense 100mv/div 610912 g17 2s/div r in = 1k r out = 20k g = 20v/v common mode rejection ratio vs frequency frequency (hz) 1 0 common mode rejection ratio (db) 120100 140 10 100 1k 10k 100k 1m 10m 610812 g09 8060 40 20 downloaded from: http:///
lt6108-1/lt6108-2 8 610812fa comparator threshold distribution hysteresis distribution hysteresis vs temperature hysteresis vs supply voltage lt6108-2 en current vs voltage comparator threshold vs temperature lt6108-1 en/ rst current vs voltage typical performance characteristics performance characteristics taken at t a = 25c, v + = 12v, v pullup = v + , v en = v en/ rst = 2.7v, r in = 100, r out = r1 + r2 = 10k, gain = 100, r c = 25.5k, c l = c lc = 2pf, unless otherwise noted. (see figure 3) temperature (c) C40 comparator threshold (mv) 408406 404 402 400 398 396 394 392 80 610812 g20 C10 20 50 125 110 65 C25 5 35 95 5 typical units temperature (c) C40 comparator hysteresis (mv) 20 1816 14 12 10 86 4 0 2 80 610812 g22 C10 20 50 125 110 65 C25 5 35 95 v + (v) 0 14 1210 86 4 2 0 30 50 610812 g23 10 20 40 60 comparator hysteresis (mv) 5 typical units en/ rst voltage (v) 0 C250 en/ rst current (na) C200 C150 C100 C50 50 10 20 30 40 610812 g24 50 60 0 en voltage (v) 0 C250 en current (na) C200 C150 C100 C50 50 10 20 30 40 610812 g25 50 60 0 comparator threshold (mv) 0 percentage of units (%) 5 15 20 25 399.2 404 610812 g19 10 396 397.6 400.8 402.8 comparator hysteresis (mv) 3 0 percentage of units (%) 5 10 15 20 30 C40c 25c 125c 4.6 6.2 7.7 9.3 10.9 12.5 610812 g21 14.1 15.7 17.3 25 power supply rejection ratiovs frequency frequency (hz) 1 0 power supply rejection ratio (db) 120100 140 160 10 100 1k 10k 100k 1m 10m 610812 g08 8060 40 20 downloaded from: http:///
lt6108-1/lt6108-2 9 610812fa comparator rise/fall time vs pull-up resistor lt6108-1 comparator step response (5mv inc overdrive) lt6108-1 comparator step response (100mv inc overdrive) comparator propagation delay vs input overdrive comparator output leakage current vs pull-up voltage typical performance characteristics performance characteristics taken at t a = 25c, v + = 12v, v pullup = v + , v en = v en/ rst = 2.7v, r in = 100, r out = r1 + r2 = 10k, gain = 100, r c = 25.5k, c l = c lc = 2pf, unless otherwise noted. (see figure 3) comparator output low voltage vs output sink current comparator input bias current vs input voltage comparator input voltage (v) C20 comparator input bias current (na) C10 0 10 C15 C5 5 0.2 0.4 0.6 0.8 610812 g28 1.0 0 125c25c C40c i outc (ma) 0 0 v ol outc (v) 0.25 0.50 0.75 1.00 1 2 610812 g29 3 125c25c C40c comparator output pull-up voltage (v) 0 C2 outc leakage current (na) 3 8 13 18 23 125c 10 20 30 40 610812 g30 50 60 C40c and 25c comparator input overdrive (mv) 0 comparator propagation delay (s) 3.0 4.0 5.0 160 610812 g31 2.01.0 2.5 3.5 4.51.5 0.5 0 40 80 120 200 rising inputlt6108-1 and lt6108-2 falling inputlt6108-2 r c pull-up resistor (k) 1 10 rise/fall time (ns) 100 1000 10000 10 100 1000 610812 g32 v oh = 0.9 ? v pullup v ol = 0.1 ? v pullup 100mv inc overdrivec l = 2pf falling input lt6108-2 rising input lt6108-1 and lt6108-2 v inc 0.5v/div 0v v outc 2v/div v en/ rst 5v/div 0v 0v 610812 g33 5s/div v + = 5v 0v v inc 0.5v/div v outc 2v/div v en/ rst 5v/div 0v0v 610812 g34 5s/div v + = 5v comparator input bias current vs input voltage comparator input voltage (v) C20 comparator input bias current (na) C10 0 10 C15 C5 5 20 40 610812 g27 60 0 125c25c C40c downloaded from: http:///
lt6108-1/lt6108-2 10 610812fa lt6108-2 comparator step response (5mv inc overdrive) lt6108-2 comparator step response (100mv inc overdrive) lt6108-1 comparator reset response senselo (pin 1): sense ampliier input. this pin must be tied to the load end of the sense resistor. en/ rst (pin 2, lt6108-1 only): enable and latch reset input. when the en/ rst pin is pulled high the lt6108-1 is enabled. when the en/ rst pin is pulled low for longer than typically 40s, the lt6108-1 will enter the shutdown mode. pulsing this pin low for between 2s and 15s will reset the comparator of the lt6108-1. en (pin 2, lt6108-2 only): enable input. when the en - able pin is pulled high the lt6108-2 is enabled. when the enable pin is pulled low for longer than typically 40s, the lt6108-2 will enter the shutdown mode outc (pin 3): open-drain comparator output. off-state voltage may be as high as 60v above v C , regardless of v + used. v C (pin 4): negative supply pin. this pin is normally con - nected to ground.inc (pin 5): this is the inverting input of the comparator. the other comparator input is internally connected to the 400mv reference. pin functions outa (pin 6): current output of the sense ampliier. this pin will source a current that is equal to the sense voltage divided by the external gain setting resistor, r in . v + (pin 7): positive supply pin. the v + pin can be con - nected directly to either side of the sense resistor, r sense . when v + is tied to the load end of the sense resistor, the sensehi pin can go up to 0.2v above v + . supply current is drawn through this pin. sensehi (pin 8): sense ampliier input. the internal sense ampliier will drive sensehi to the same potential as senselo. a resistor (typically r in ) tied from supply to sensehi sets the output current, i out = v sense /r in , where v sense is the voltage developed across r sense . exposed pad (pin 9, dcb package only): v C . the exposed pad may be left open or connected to device v C . connect - ing the exposed pad to a v C plane will improve thermal management in high voltage applications. the exposed pad should not be used as the primary connection for v C . typical performance characteristics performance characteristics taken at t a = 25c, v + = 12v, v pullup = v + , v en = v en/ rst = 2.7v, r in = 100, r out = r1 + r2 = 10k, gain = 100, r c = 25.5k, c l = c lc = 2pf, unless otherwise noted. (see figure 3) v inc 0.5v/div 0v v outc 1v/div 610812 g35 5s/div 0v v + = 5v v inc 0.5v/div 0v v outc 1v/div 610812 g36 5s/div 0v v + = 5v 0v v outc 5v/div v en/ rst 2v/div 0v 5s/div 610812 g37 downloaded from: http:///
lt6108-1/lt6108-2 11 610812fa block diagrams figure 1. lt6108-1 block diagram (latching comparator) figure 2. lt6108-2 block diagram (non-latching comparator) 100 outa C + C + 7 8 1 6 inc 5 610812 f01 v + v C v C v C v C v + 3k v + 3k sensehi lt6108-1 senselo 200na reset overcurrent flag 2 en/ rst 3 outc 34v 6v enable and reset timing v C 4 400mv reference 100 outa C + C + 7 8 1 6 inc 5 610812 f02 v + v C v C v C v C v + 3k v + 3k sensehi lt6108-2 senselo 100na overcurrent flag 2 en 3 outc 34v 6v v C 4 400mv reference downloaded from: http:///
lt6108-1/lt6108-2 12 610812fa applications information the l t6108 high side current sense ampliier provides accurate monitoring of currents through an external sense resistor. the input sense voltage is level-shifted from the sensed power supply to a ground referenced output and is ampliied by a user-selected gain to the output. the output voltage is directly proportional to the current low - ing through the sense resistor. the lt6108 comparator has a threshold set with a built-in 400mv precision reference and has 10mv of hysteresis. the open-drain output can be easily used to level shift to digital supplies. ampliier theory of operation an internal sense ampliier loop forces sensehi to have the same potential as senselo as shown in figure 3. connecting an external resistor, r in , between sensehi and v supply forces a potential, v sense , across r in . a corresponding current, i outa , equal to v sense /r in , will low through r in . the high impedance inputs of the sense ampliier do not load this current, so it will low through an internal mosfet to the output pin, outa. the output current can be transformed back into a voltage by adding a resistor from outa to v C (typically ground). the output voltage is then: v out = v C + i outa ? r out where r out = r1 + r2 as shown in figure 3. table 1. example gain conigurations gain r in r out v sense for v out = 5v i outa at v out = 5v 20 499 10k 250mv 500a 50 200 10k 100mv 500a 100 100 10k 50mv 500a useful equations input voltage: v sense = i sense ? r sense voltage gain: v out v sense = r out r in current gain: i outa i sense = r sense r in note that v sense(max) can be exceeded without damag - ing the ampliier, however, output accuracy will degrade as v sense exceeds v sense(max) , resulting in increased output current, i outa . selection of external current sense resistor the external sense resistor, r sense , has a signiicant effect on the function of a current sensing system and must be chosen with care. first, the power dissipation in the resistor should be considered. the measured load current will cause power dissipation as well as a voltage drop in r sense . as a result, the sense resistor should be as small as possible while still providing the input dynamic range required by the measurement. note that the input dynamic range is the difference between the maximum input signal and the minimum accurately reproduced signal, and is limited primarily by input dc offset of the internal sense ampli - ier of the lt6108. to ensure the speciied performance, r sense should be small enough that v sense does not exceed v sense(max) under peak load conditions. as an example, an application may require the maximum sense voltage be 100mv. if this application is expected to draw 2a at peak load, r sense should be set to 50m. once the maximum r sense value is determined, the mini - mum sense resistor value will be set by the resolution or dynamic range required. the minimum signal that can be accurately represented by this sense ampliier is limited by the input offset. as an example, the lt6108 has a maximum input offset of 125v. if the minimum current is 20ma, a sense resistor of 6.25m will set v sense to 125v. this is the same value as the input offset. a larger sense resistor will reduce the error due to offset by increasing the sense voltage for a given load current. choosing a 50m r sense will maximize the dynamic range and provide a system that has 100mv across the sense resistor at peak load (2a), while input offset causes an error equivalent to only 2.5ma of load current. in the previous example, the peak dissipation in r sense is 200mw. if a 5m sense resistor is employed, then the effective current error is 25ma, while the peak sense voltage is reduced to 10mv at 2a, dissipating only 20mw. downloaded from: http:///
lt6108-1/lt6108-2 13 610812fa applications information the low offset and corresponding large dynamic range of the lt6108 make it more lexible than other solutions in this respect. the 125v maximum offset gives 72db of dynamic range for a sense voltage that is limited to 500mv max. sense resistor connection kelvin connection of the sensehi and senselo inputs to the sense resistor should be used in all but the lowest power applications. solder connections and pc board interconnections that carry high currents can cause sig - niicant error in measurement due to their relatively large resistances. one 10mm 10mm square trace of 1oz copper is approximately 0.5m. a 1mv error can be caused by as little as 2a lowing through this small interconnect. this will cause a 1% error for a full-scale v sense of 100mv. a 10a load current in the same interconnect will cause a 5% error for the same 100mv signal. by isolating the sense traces from the high current paths, this error can be reduced by orders of magnitude. a sense resistor with integrated kelvin sense terminals will give the best results. figure 3 illustrates the recommended method for connect - ing the sensehi and senselo pins to the sense resistor. selection of external input gain resistor, r in r in should be chosen to allow the required speed and resolution while limiting the output current to 1ma. the maximum value for r in is 1k to maintain good loop sta - bility. for a given v sense , larger values of r in will lower power dissipation in the lt6108 due to the reduction in i out while smaller values of r in will result in faster response time due to the increase in i out . if low sense currents must be resolved accurately in a system that has a very wide dynamic range, a smaller r in may be used if the maximum i outa current is limited in another way, such as with a schottky diode across r sense (figure 4). this will reduce the high current measurement accuracy by limiting the result, while increasing the low current measurement resolution. figure 3. lt6108-1 typical connection figure 4. shunt diode limits maximum input voltage to allow better low input resolution without overranging outa i outa C + v + c1 sensehi inc 6 7 85 610812 f03 v + v + v C lt6108-1 senseloen/ rst outc 12 3 4 v reset r c v pullup load v supply v sense r sense overcurrent flag r in +C *r out = r1 + r2 v C i sense = v sense r sense r1* r2* c l v out 400mv reference c lc C + d sense r sense v + load 610812 f04 downloaded from: http:///
lt6108-1/lt6108-2 14 610812fa applications information this approach can be helpful in cases where occasional bursts of high currents can be ignored. care should be taken when designing the board layout for r in , especially for small r in values. all trace and inter - connect resistances will increase the effective r in value, causing a gain error. the power dissipated in the sense resistor can create a thermal gradient across a printed circuit board and con - sequently a gain error if r in and r out are placed such that they operate at different temperatures. if signiicant power is being dissipated in the sense resistor then care should be taken to place r in and r out such that the gain error due to the thermal gradient is minimized. selection of external output gain resistor, r out the output resistor, r out , determines how the output cur - rent is converted to voltage. v out is simply i outa ? r out . typically, r out is a combination of resistors conigured as a resistor divider which has a voltage tap going to the comparator input to set the comparator threshold. in choosing an output resistor, the maximum output volt - age must irst be considered. if the subsequent circuit is a buffer or adc with limited input range, then r out must be chosen so that i outa(max) ? r out is less than the allowed maximum input range of this circuit. in addition, the output impedance is determined by r out . if another circuit is being driven, then the input impedance of that circuit must be considered. if the subsequent circuit has high enough input impedance, then almost any use - ful output impedance will be acceptable. however, if the subsequent circuit has relatively low input impedance, or draws spikes of current such as an adc load, then a lower output impedance may be required to preserve the accurac y of the output. more information can be found in the output filtering section. as an example, if the input impedance of the driven circuit, r in(driven) , is 100 times r out , then the accuracy of v out will be reduced by 1% since: v out = i outa ? r out ? r in(driven) r out + r in(driven) = i outa ? r out ? 100 101 = 0.99 ? i outa ? r out ampliier error sourcesthe current sense system uses an ampliier and resistors to apply gain and level-shift the result. consequently, the output is dependent on the characteristics of the ampliier, such as gain error and input offset, as well as the matching of the external resistors. ideally, the circuit output is: v out = v sense ? r out r in ; v sense = r sense ? i sense in this case, the only error is due to external resistor mismatch, which provides an error in gain only. however, offset voltage, input bias current and inite gain in the ampliier can cause additional errors: output voltage error, ? v out(vos) , due to the ampliier dc offset voltage, v os ? v out(vos) = v os ? r out r in the dc offset voltage of the ampliier adds directly to the value of the sense voltage, v sense . as v sense is increased, accuracy improves. this is the dominant error of the system and it limits the available dynamic range. output voltage error, ? v out(ibias) , due to the bias currents i b + and i b C the ampliier bias current i b + lows into the senselo pin while i b C lows into the sensehi pin. the error due to i b is the following: ? v out(ibias) = r out i b + ? r sense r in ?i b ? ?? ? ?? ? since i b + i b C = i bias , if r sense << r in then, ? v out(ibias) = Cr out (i bias ) it is useful to refer the error to the input: ? v vin(ibias) = Cr in (i bias ) for instance, if i bias is 100na and r in is 1k, the input re - ferred error is 100v. this error becomes less signiicant as the value of r in decreases. the bias current error can downloaded from: http:///
lt6108-1/lt6108-2 15 610812fa applications information output current limitations due to power dissipation the lt6108 can deliver a continuous current of 1ma to the outa pin. this current lows through r in and enters the current sense ampliier via the sensehi pin. the power dissipated in the lt6108 due to the output signal is: p out = (v sensehi C v outa ) ? i outa since v sensehi v + , p outa (v + C v outa ) ? i outa there is also power dissipated due to the quiescent power supply current: p s = i s ? v + the comparator output current lows into the comparator output pin and out of the v C pin. the power dissipated in the lt6108 due to the comparator is often insigniicant and can be calculated as follows: p outc = (v outc C v C ) ? i outc the total power dissipated is the sum of these dissipations: p total = p outa + p outc + p s at maximum supply and maximum output currents, the total power dissipation can exceed 150mw. this will cause signiicant heating of the lt6108 die. in order to prevent damage to the lt6108, the maximum expected dissipa - tion in each application should be calculated. this number can be multiplied by the ja value, 163c/w for the ms8 package or 64c/w for the dfn, to ind the maximum expected die temperature. proper heat sinking and thermal relief should be used to ensure that the die temperature does not exceed the maximum rating. output filtering the ac output voltage, v out , is simply i outa ? z out . this makes iltering straightforward. any circuit may be used which generates the required z out to get the desired ilter response. for example, a capacitor in parallel with r out will give a lowpass response. this will reduce noise at the output, and may also be useful as a charge reservoir to keep the output steady while driving a switching circuit be reduced if an external resistor, r in + , is connected as shown in figure 5, the error is then reduced to: v out(ibias) = r out ? i os ; i os = i b + C i b C minimizing low current errors will maximize the dynamic range of the circuit. figure 6. gain error vs resistor tolerance figure 5. r in + reduces error due to i b sensehi lt6108 i sense r sense v + 7v C 4 v + r in v batt senselo 81 outa 6 610812 f05 r out v out r in + C + resistor tolerance (%) 0.01 0.01 resulting gain error (%) 0.1 1 10 0.1 1 10 610812 f06 r in = 100 r in = 1k output voltage error, ? v out(gain error) , due to external resistors the lt6108 exhibits a very low gain error. as a result, the gain error is only signiicant when low tolerance resistors are used to set the gain. note the gain error is systematically negative. for instance, if 0.1% resistors are used for r in and r out then the resulting worst-case gain error is C0.4% with r in = 100. figure 6 is a graph of the maximum gain error which can be expected versus the external resistor tolerance. downloaded from: http:///
lt6108-1/lt6108-2 16 610812fa applications information such as a mux or adc. this output capacitor in parallel with r out will create an output pole at: f ?3db = 1 2 ? ? r out ? c l senselo, sensehi rangethe difference between v batt (see figure 7) and v + , as well as the maximum value of v sense , must be considered to ensure that the senselo pin doesnt exceed the range listed in the electrical characteristics table. the senselo and sensehi pins of the lt6108 can function from 0.2v above the positive supply to 33v below it. these operat - ing voltages are limited by internal diode clamps shown in figures 1 and 2. on supplies less than 35.5v, the lower range is limited by v C + 2.5v. this allows the monitored supply, v batt , to be separate from the lt6108 positive supply as shown in figure 7. figure 8 shows the range of operating voltages for the senselo and sensehi inputs, for different supply voltage inputs (v + ). the senselo and sensehi range has been designed to allow the lt6108 to monitor its own supply current (in addition to the load), as long as v sense is less than 200mv. this is shown in figure 9. minimum output voltage the output of the l t6108 current sense ampliier can produce a non-zero output voltage when the sense voltage is zero. this is a result of the sense ampliier v os being forced across r in as discussed in the output voltage er - ror, ? v out(vos) section. figure 10 shows the effect of the input offset voltage on the transfer function for parts at the v os limits. with a negative offset voltage, zero input figure 9. lt6108 supply current monitored with load figure 7. v + powered separately from load supply (v b att ) figure 8. allowable senselo, sensehi voltage range figure 10. ampliier output voltage vs input sense voltage sensehi lt6108 i sense r sense v + 7 6 v C 4 v + r in v batt senselo 81 outa 610812 f07 r out v out C + 6027 allowable operating voltage on senselo and senshi inputs (v) 2.8 10 20 20.2v 40.2v 30 40 50 2.5 2.7 10 20 30 40 50 35.5 v + (v) 60 610812 f08 valid senselo/ sensehi range sensehi lt6108 i sense r sense v + 7 6 v C 4 r in v batt senselo 81 outa 610812 f09 r out v out C + input sense voltage (v) 0 output voltage (mv) 40 80 120 20 60 100 200 400 600 800 610812 f10 1000 100 0 300 500 700 900 v os = C125v g = 100 v os = 125v downloaded from: http:///
lt6108-1/lt6108-2 17 610812fa sense voltage produces an output voltage. with a positive offset voltage, the output voltage is zero until the input sense voltage exceeds the input offset voltage. neglect - ing v os , the output circuit is not limited by saturation of pull-down circuitry and can reach 0v. response time the l t6108 ampliier is designed to exhibit fast response to inputs for the purpose of circuit protection or current monitoring. this response time will be affected by the external components in two ways, delay and speed. if the output current is very low and an input transient occurs, there may be an increased delay before the output voltage begins to change. the typical performance characteristics show that this delay is short and it can be improved by increasing the minimum output current, either by increasing r sense or decreasing r in . note that the typical performance characteristics are labeled with respect to the initial sense voltage. the speed is also affected by the external components. using a larger r out will decrease the response time, since v out = i outa ? z out where z out is the parallel combination of r out and any parasitic and/or load capacitance. note that reducing r in or increasing r out will both have the effect of increasing the voltage gain of the circuit. if the output capacitance is limiting the speed of the system, r in and r out can be decreased together in order to maintain the desired gain and provide more current to charge the output capacitance. the response time of the comparator is the sum of the propagation delay and the fall time. the propagation delay is a function of the overdrive voltage on the input of the comparator. a larger overdrive will result in a lower propaga - tion delay. this helps achieve a fast system response time to fault events. the fall time is affected by the load on the output of the comparator as well as the pull-up voltage. the lt6108 ampliier has a typical response time of 500ns and the comparators have a typical response time of 500ns. when conigured as a system, the ampliier output drives the comparator input causing a total system response time which is typically greater than that implied by the individually speciied response times. this is due to the applications information overdrive on the comparator input being determined by the speed of the ampliier output. internal reference and comparator the integrated precision reference and comparator com - bined with the high precision current sense allow for rapid and easy detection of abnormal load currents. this is often critical in systems that require high levels of safety and reliability. the lt6108-1 comparator is optimized for fault detection and is designed with a latching output. the latch - ing output prevents faults from clearing themselves and requires a separate system or user to reset the output. in applications where the comparator output can intervene and disconnect loads from the supply, a latched output is required to avoid oscillation. the latching output is also useful for detecting problems that are intermittent. the comparator output on the lt6108-2 is non-latching and can be used in applications where a latching output is not desired. the comparator has one input available externally. the other comparator input is connected internally to the 400mv precision reference. the input threshold (the voltage which causes the output to transition from high to low) is designed to be equal to that of the reference. the reference voltage is established with respect to the device v C connection. comparator input the comparator input can swing from v C to 60v regardless of the supply voltage used. the input current for inputs well above the threshold is just a few pas. with decreas - ing input voltage, a small bias current begins to be drawn out of the input near the threshold, reaching 50na max when at ground potential. note that this change in input bias current can cause a small nonlinearity in the outa transfer function if the comparator input is coupled to the ampliier output with a voltage divider. for example, if the maximum comparator input current is 50na, and the resistance seen looking out of the comparator input is 1k, then a change in output voltage of 50v will be seen on the analog output when the comparator input voltage passes through its threshold. downloaded from: http:///
lt6108-1/lt6108-2 18 610812fa setting comparator threshold the comparator has an internal 400mv precision reference. in order to set the trip point of the lt6108 comparator as conigured in figure 11, the input sense voltage at which the comparator will trip, v sense(trip) must be calculated: v sense(trip) = i sense(trip) ? r sense the selection of r in is discussed in the selection of exter - nal input gain resistor r in section. once r in is selected, r out can be calculated: r out = r in 400mv v sense(trip) since the ampliier output is connected directly to the comparator input, the gain from v sense to v out is: a v = 400mv v sense(trip) applications information as shown in figure 12, r2 can be used to increase the gain from v sense to v out without changing v sense(trip) . as before, r1 can be easily calculated: r1 = r in 400mv v sense(trip) the gain is now: a v = r1 + r2 r in this gain equation can be easily solved for r2: r2 = a v ? r in C r1 if the coniguration of figure 11 gives too much gain, r2 can be used to reduce the gain without changing v sense(trip) as shown in figure 13. a v can be easily calculated: a v = r1 r in outa i outa C + v + c1 sensehi inc 6 7 85 610812 f11 v + v + v C lt6108-1 senseloen/ rst outc 12 3 4 v reset r c v pullup load v supply v sense r sense overcurrent flag r in +C v C i sense = v sense r sense r out c l v out 400mv reference c lc C + figure 11. basic comparator coniguration downloaded from: http:///
lt6108-1/lt6108-2 19 610812fa applications information figure 12: comparator coniguration with increased a v figure 13: comparator coniguration with reduced a v outa i outa C + v + c1 sensehi inc 6 7 85 610812 f12 v + v + v C lt6108-1 senseloen/ rst outc 12 3 4 v reset r c v pullup load v supply v sense r sense overcurrent flag r in +C v C i sense = v sense r sense r1 r2 c l v out 400mv reference c lc C + outa i outa C + v + c1 sensehi inc 6 7 85 610812 f13 v C v + v + v C lt6108-1 senseloen/ rst outc 12 3 4 v reset r c v pullup load v supply v sense r sense overcurrent flag r in +C i sense = v sense r sense r1 r2 c l v out 400mv reference c lc C + downloaded from: http:///
lt6108-1/lt6108-2 20 610812fa figure 14. comparator output transfer characteristics this gain equation can be easily solved for r1: r1 = a v ? r in the value of r2 can be calculated: r2 = 400mv ? r in ? v sense(trip) ? r1 v sense(trip) hysteresis the comparator has a typical built-in hysteresis of 10mv to simplify design, ensure stable operation in the pres - ence of noise at the input, and to reject supply noise that might be induced by state change load transients. the hysteresis is designed such that the threshold voltage is altered when the output is transitioning from low to high as is shown in figure 14. external positive feedback circuitry can be employed to increase the effective hysteresis if desired, but such applications information circuitry will have an effect on both the rising and fall - ing input thresholds, v th (the actual internal threshold remains unaffected). figure 15 shows how to add additional hysteresis to the comparator. r5 can be calculated from the ampliier output current which is required to cause the comparator output to trip, i over . r5 = 400mv i over , assuming r1 + r2 ( ) >> r5 to ensure (r1 + r2) >> r5, r1 should be chosen such that r1 >> r5 so that v outa does not change signiicantly when the comparator trips. r3 should be chosen to allow suficient v ol and compara - tor output rise time due to capacitive loading.r2 can be calculated: r2 = r1 ? v dd ? 390mv v hys(extra) ?? ? ?? ? note that the hysteresis being added, v hys(extra) , is in addition to the typical 10mv of built-in hysteresis. for very large values of r2 pcb related leakage may become an issue. a tee network can be implemented to reduce the required resistor values. figure 15. inverting comparator with added hysteresis C + v + v + v C inc v C 4 610812 f15 outa 6 7 5 v + v + sensehi lt6108-1 r in r sense i load v + senselooutc 3 1 8 400mv reference r3 r4 r5 r1 vth r2 v dd C + v hys outc v th increasing v inc 610812 f14 downloaded from: http:///
lt6108-1/lt6108-2 21 610812fa figure 16. comparator reset functionality the approximate total hysteresis is: v hys = 10mv + r1 ? v dd ? 390mv r2 ?? ? ?? ? for example, to achieve i over = 900a with 50mv of total hysteresis, r5 = 442. choosing r1 = 4.42k, r3 = 10k and v dd = 5v results in r2 = 513k. the analog output voltage will also be affected when the comparator trips due to the current injected into r5 by the positive feedback. because of this, it is desirable to have (r1 + r2) >> r5. the maximum v outa error caused by this can be calculated as: ? v outa = v dd ? r5 r1 + r2 + r5 ?? ? ?? ? in the previous example, this is an error of 4.3mv at the output of the ampliier or 43v at the input of the ampliier assuming a gain of 100. when using the comparator with its input decoupled from the output of the ampliier it may be driven directly by a voltage source. it is useful to know the threshold voltage equations with additional hysteresis. the input rising edge threshold which causes the output to transition from high to low is: v th r ( ) = 400mv ? 1 + r1 r2 ?? ? ?? ? the input falling edge threshold which causes the output to transition from low to high is: v th f ( ) = 390mv 1 + r1 r2 ?? ? ?? ? ? v dd r1 r2 ?? ? ?? ? comparator outputthe comparator output can maintain a logic-low level of 150mv while sinking 500a. the output can sink higher currents at elevated v ol levels as shown in the typical performance characteristics. load currents are conducted to the v C pin. the output off-state voltage may range between 0v and 60v with respect to v C , regardless of the supply voltage used. applications information en/ rst pin (lt6108-1 only) the en/ rst pin performs the two functions of resetting the latch on the comparator as well as shutting down the lt6108-1. when this pin is pulled high the lt6108-1 is enabled. after powering on the lt6108-1, the comparator must be reset in order to guarantee a valid state at its output. applying a pulse to the en/ rst pin will reset the compara - tor from its tripped low state as long as the input on the comparator is below the threshold and hysteresis. for example, if v inc is pulled higher than 400mv and latches the comparator, a reset pulse will not reset that comparator unless its input is held below the threshold by a voltage greater than the 10mv typical hysteresis. the comparator output typically unlatches in 0.5s with 2pf of capacitive load. increased capacitive loading on the comparator output will cause an increased unlatch time. figure 16 shows the reset functionality of the en/ rst pin. the width of the pulse applied to reset the compara - tor must be greater than t rpw(min) (2s) but less than t rpw(max) (15s). applying a pulse that is longer than 40s typically (or tying the pin low) will cause the part to enter shutdown. once the part has entered shutdown, the supply current will be reduced to 3a typically and the ampliier, comparator and reference will cease to function until the en/ rst pin is transitioned high. when the part is disabled, both the ampliier and comparator outputs are high impedance. when the en/ rst pin is transitioned from low to high to enable the part, the ampliier output pmos can turn on momentarily causing typically 1ma of current to low into the sensehi pin and out of the outa pin. once the ampliier is fully on, the output will go to the correct en/ rst outc t reset 0.5s (typical) 610812 f16 t rpw(max) 15s comparator reset reset pulse width limits t rpw(min) 2s downloaded from: http:///
lt6108-1/lt6108-2 22 610812fa figure 17. ampliier enable response current. figure?17 shows this behavior and the impact it has on v outa . circuitry connected to outa can be protected from these transients by using an external diode to clamp v outa , or a capacitor to ilter v outa . applications information power up after powering on the lt6108-1, the comparator must be reset in order to guarantee a valid state at its output. fast supply ramps may cause a supply current transient during start-up as shown in the typical performance characteristics. this current can be lowered by reducing the edge speed of the supply. reverse-supply protection the lt6108 is not protected internally from external rever - sal of supply polarity. to prevent damage that may occur during this condition, a schottky diode should be added in series with v C (figure 18). this will limit the reverse current through the lt6108. note that this diode will limit the low voltage operation of the lt6108 by effectively reducing the supply voltage to the part by v d . also note that the comparator reference, comparator output and en/ rst input are referenced to the v C pin. in order to preserve the precision of the reference and to avoid driving the comparator inputs below v C , r2 must connect to the v C pin. this will shift the ampliier output voltage up by v d . v outa can be accurately measured 50s/div 0v v en/ rst 2v/div 0v v outa 2v/div 610812 f17 v + = 60v r in = 100 r out = 10k C + v + v + v C inc v C 4 v d +C v outa +C 610812 f18 outa 6 7 5 v + v + sensehi lt6108-1 r in r sense i load v dd v dd senselooutc 3 en/ rst 2 1 8 400mv reference r3 r1 r2 v dd C + en pin (lt6108-2) when this pin is pulled high, the lt6108-2 is enabled. when the enable pin is pulled low for longer than 40s typically, the lt6108-2 will enter the shutdown mode. figure 18. schottky prevents damage during supply reversal downloaded from: http:///
lt6108-1/lt6108-2 23 610812fa applications information typical applications mcu interfacing with hardware interrupts sensehi senselo outa 0.1 v + 100 lt6108-1 v C to load v out adc in 8.66k 1.33k inc v + en/ rst outc 6 15 4 8 72 3 reset 6108 ta03 10k 5v v out /adc in atmega1280 pb0pb1 pcint2pcint3 adc2 pb5 56 7 2 3 1 overcurrent routine reset comparator mcu interupt outc goes low 5v0v 610812 ta03b example: the comparator is set to have a 300ma overcurrent threshold. the mcu will receive the comparator output as a hardware interrupt and immediately run an appropriate fault routine. overcurrent battery fault protection sensehi senselo outa 0.1 r10100 lt6108-1 v C to load v out 9.53k 475 0.8aovercurrent detection inc v + en/ rst 6 15 4 outc 8 7 10k 100k 6.2v* irf9640 2 5v 3 reset 610812 ta02 100k 2n7000 *cmh25234b + + + + 10f 12 lithium 40v cell stack differentially across r1 and r2. the comparator output low voltage will also be shifted up by v d . the en/ rst pin threshold is referenced to the v C pin. in order to provide valid input levels to the lt6108 and avoid driving en/ rst below v C the negative supply of the driving circuit should be tied to v C of the lt6108. downloaded from: http:///
lt6108-1/lt6108-2 24 610812fa typical applications simpliied dc motor torque control power-on reset or disconnect using timerblox ? circuit the igure above shows a simpliied dc motor control circuit. the circuit controls motor current, which is pro - portional to motor torque; the lt6108 is used to provide current feedback to an integrator that servos the motor current to the current set point. the ltc ? 6992 is used to convert the output of the difference amp to the motors pwm control signal. sensehi senselo outa 8 1 65 72 3 4 lt6108-1 v C 9k 100k 23 7 ltc6246 4 6 13 6 irf640 5v 1n5818 0.1 v motor 5 4 2 0.47f v out current set point (0v to 5v) 1k 1m 610812 ta04 1k 78.7k 100k 280k inc v + en/ rst outc reset 100f +C ltc6992-1 v + gnd 5v 1f brushed dc motor (0a to 5a) mabuchi rs-540sh modset out div C + v + v C v C 4 610812 ta06 v + 400mv reference v + r in 100 r sense i load outa 6 inc 5 7 sensehi lt6108-1 5v senselooutc en/ rst 81 3 2 r19.53k r2499 r710k r41m r5487k r6 30k trig c1 0.1f q12n2222 out gnd v + set div ltc6993-3 5v creates a delayed 10s reset pulse on start-up optional: discharges c1 when supply is disconnected C + the ltc6993-3 provides a 10s reset pulse to the lt6108-1. the reset pulse is delayed by r4 and c1 whose time constant must be greater than 10ms and longer than the supply turn-on time. optional components r6 and q1 discharge capacitor c1 when the supply and/or ground are discon - nected. this ensures that when the power supply and/or ground are restored, capacitor c1 can fully recharge and trigger the ltc6993-3 to produce another comparator reset pulse. these optional components are particularly useful if the power and/or ground connections are intermittent, as can occur when pcb are plugged into a connector. downloaded from: http:///
lt6108-1/lt6108-2 25 610812fa typical applications an external latch is implemented with positive feedback. r6 and c1 provide a reset pulse on power-up. the time constant formed by r6 and c1 should be set slower than that of the supply. optional components r9 and q1 dis - charge capacitor c1 when the supply and/or ground are disconnected. this ensures that when the power supply and/or ground are restored, capacitor c1 can fully recharge. while c1 is charging, the nor gate output is low, ensuring that the comparator powers up in the correct state. these optional components are particularly useful if the power and/or ground connections are intermittent, as can occur when pcb are plugged into a connector. r4 and r5 are optional and minimize the movement of the rising input threshold voltage. C + v + v C v C 4 610812 ta06 v + 400mv reference v + r in 100 r sense i load outa 6 inc 5 vth 7 sensehi lt6108-2 5v senselooutc 81 3 r79.53k r8499 r1 24.9k r2 200k v dd r61m *optional component c1 0.1f q1*2n2222 r4* 3.4k r5*100k r9*30k r310k C + lt6108-2 with external latch and power-on reset or disconnect the input rising edge threshold which causes the output to transition from high to low is: v th r ( ) = 400mv if r4 = r5 ? 400mv v dd ? 400mv ?? ? ?? ? the input falling edge which causes the output to transi - tion from low to high is: v th f ( ) = 390mv ? r1 ? 1 r1 + 1 r2 + r4||r5 ?? ? ?? ? ? v dd ? r1 r2 + r4||r5 ?? ? ?? ? downloaded from: http:///
lt6108-1/lt6108-2 26 610812fa typical applications precision power-on reset using timerblox circuit C + v + v C v C 4 610812 ta08 v + 400mv reference v + r in 100 r sense i load outa 6 inc 5 7 sensehi lt6108-1 5v senselooutc en/ rst 81 3 2 r19.53k r2499 r310k C + r8 100k r4487k c2 0.1f r5681k r61m 10s reset pulse generator c1 0.1f r7191k triggnd set ltc6994-1 1 second delay on start-up out v + div trig out gnd v + set div ltc6993-1 downloaded from: http:///
lt6108-1/lt6108-2 27 610812fa package description please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. msop (ms8) 0307 rev f 0.53 0.152 (.021 .006) seating plane note:1. dimensions in millimeter/(inch) 2. drawing not to scale 3. dimension does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.152mm (.006") per side 4. dimension does not include interlead flash or protrusions. interlead flash or protrusions shall not exceed 0.152mm (.006") per side 5. lead coplanarity (bottom of leads after forming) shall be 0.102mm (.004") max 0.18 (.007) 0.254 (.010) 1.10 (.043) max 0.22 C 0.38 (.009 C .015) typ 0.1016 0.0508 (.004 .002) 0.86 (.034) ref 0.65 (.0256) bsc 0 C 6 typ detail a detail a gauge plane 1 2 3 4 4.90 0.152 (.193 .006) 8 7 6 5 3.00 0.102 (.118 .004) (note 3) 3.00 0.102 (.118 .004) (note 4) 0.52 (.0205) ref 5.23 (.206) min 3.20 C 3.45 (.126 C .136) 0.889 0.127 (.035 .005) recommended solder pad layout 0.42 0.038 (.0165 .0015) typ 0.65 (.0256) bsc ms8 package 8-lead plastic msop (reference ltc dwg # 05-08-1660 rev f) downloaded from: http:///
lt6108-1/lt6108-2 28 610812fa package description please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. 3.00 0.10 (2 sides) 2.00 0.10 (2 sides) note:1. drawing is not a jedec package outline 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package 0.40 0.10 bottom viewexposed pad 0.75 0.05 r = 0.115 typ r = 0.05 typ 1.35 ref 1 4 8 5 pin 1 bar top mark (see note 6) 0.200 ref 0.00 C 0.05 (dcb8) dfn 0106 rev a 0.23 0.05 0.45 bsc pin 1 notchr = 0.20 or 0.25 45 chamfer 0.25 0.05 1.35 ref recommended solder pad pitch and dimensions apply solder mask to areas that are not soldered 2.10 0.05 0.70 0.05 3.50 0.05 packageoutline 0.45 bsc 1.35 0.10 1.35 0.05 1.65 0.10 1.65 0.05 dcb package 8-lead plastic dfn (2mm 3mm) (reference ltc dwg # 05-08-1718 rev a) downloaded from: http:///
lt6108-1/lt6108-2 29 610812fa 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 12/12 addition of a-grade performance and electrical characteristics addition of a-grade order information clariication to absolute maximum short circuit duration clariication to nomenclature used in typical performance characteristics clariication to description of en/ rst pin function internal reference block redrawn for consistencyadditional information provided to reverse supply protection correction to overcurrent battery fault protection diagram 1, 3, 4, 5, 12, 13, 16 (fig10), 28 22 6, 7, 9 10 11, 13, 18, 19 2223 downloaded from: http:///
lt6108-1/lt6108-2 30 610812fa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com ? linear technology corporation 2011 lt 1212 rev a ? printed in usa related parts typical application adc driving application part number description comments lt1787 bidirectional high side current sense ampliier 2.7v to 60v, 75v offset, 60a quiescent, 8v/v gain ltc4150 coulomb counter/battery gas gauge indicates charge quantity and polarity lt6100 gain-selectable high side current sense ampliier 4.1v to 48v, gain settings: 10, 12.5, 20, 25, 40, 50v/v ltc6101 high voltage high side current sense ampliier up to 100v, resistor set gain, 300v offset, sot-23 ltc6102 zero drift high side current sense ampliier up to 100v, resistor set gain, 10v offset, msop8/dfn ltc6103 dual high side current sense ampliier 4v to 60v, resistor set gain, 2 independent amps, msop8 ltc6104 bidirectional high side current sense ampliier 4v to 60v, separate gain control for each direction, msop8 lt6105 precision rail-to-rail input current sense amplifer C0.3v to 44v input range, 300v offset, 1% gain error lt6106 low cost high side current sense ampliier 2.7v to 36v, 250v offset, resistor set gain, sot-23 lt6107 high temperature high side current sense ampliier 2.7v to 36v, C55c to 150c, fully tested: C55c, 25c, 150c lt6109 high side current sense ampliier with reference and comparators 2.7v to 60v, 125v, resistor set gain, 1.25% threshold error lt6700 dual comparator with 400mv reference 1.4v to 18v, 6.5a supply current sensehi senselo outa 0.1 sense low sense high lt6108-1 v C out 8.66k 0.1f 0.1f 1.33k inc v + en/ rst outc 6 15 4 8 72 3 v cc v ref reset 6108 ta05 in v cc 10k in + ltc2470 overcurrent comp tomcu 100 the low sampling current of the ltc2470 16-bit delta sigma adc is ideal for the lt6108. downloaded from: http:///

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