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1 lt1764 series 1764fb 3a, fast transient response, low noise, ldo regulators optimized for fast transient response output current: 3a dropout voltage: 340mv at 3a low noise: 40 v rms (10hz to 100khz) 1ma quiescent current wide input voltage range: 2.7v to 20v no protection diodes needed controlled quiescent current in dropout fixed output voltages: 1.5v, 1.8v, 2.5v, 3.3v adjustable output from 1.21v to 20v <1 a quiescent current in shutdown stable with 10 f output capacitor reverse battery protection no reverse current thermal limiting available in 5-lead to-220, dd and 16-leadtssop packages the lt 1764 is a low dropout regulator optimized for fast transient response. the device is capable of supplying 3aof output current with a dropout voltage of 340mv. oper- ating quiescent current is 1ma, dropping to < 1 a in shutdown. quiescent current is well controlled; it does notrise in dropout as it does with many other regulators. in addition to fast transient response, the lt1764 has very low output voltage noise which makes the device ideal for sensitive rf supply applications. output voltage range is from 1.21v to 20v. the lt1764 regulators are stable with output capacitors as low as 10 f. internal protection circuitry includes reverse battery pro-tection, current limiting, thermal limiting and reverse cur- rent protection. the device is available in fixed output voltages of 1.5v, 1.8v, 2.5v, 3.3v and as an adjustable device with a 1.21v reference voltage. the lt1764 regu- lators are available in 5-lead to-220, dd and exposed pad 16-lead tssop packages. dropout voltage 3.3v in to 2.5v out regulator 3.3v to 2.5v logic power supply post regulator for switching supplies features descriptio u applicatio s u typical applicatio u in shdn 10 f 1764 ta01 out v in > 3v sense gnd lt1764-2.5 2.5v3a 10 f + + load current (a) 0 0.5 dropout voltage (mv) 1.0 2.0 1.5 2.5 3.0 1764 ta02 400350 300 250 200 150 100 50 0 , ltc and lt are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. protected by u.s. patents, including 6144250, 6118263. downloaded from: http:///
2 lt1764 series 1764fb absolute m axi m u m ratings w ww u package/order i n for m atio n w u u (note 1) in pin voltage ........................................................ 20v out pin voltage .................................................... 20v input to output differential voltage (note 12) ....... 20v sense pin voltage ............................................... 20v adj pin voltage ...................................................... 7v shdn pin voltage ................................................. 20v output short-circuit duration ......................... indefinite operating junction temperature range 40 c to 125 c storage temperature range ................. 65 c to 150 c lead temperature (soldering, 10 sec).................. 300 c consult ltc marketing for parts specified with wider operating temperature ranges. order options tape and reel: add #tr lead free: add #pbf lead free tape and reel: add #trpbflead free part marking: http://www.linear.com/leadfree/ lt1764etlt1764et-1.5 lt1764et-1.8 lt1764et-2.5 lt1764et-3.3 order part number lt1764eqlt1764eq-1.5 lt1764eq-1.8 lt1764eq-2.5 lt1764eq-3.3 order part number t jmax = 150 c, ja = 30 c/ w *pin 5 = sense for lt1764-1.5/lt1764-1.8/ lt1764-2.5/lt1764-3.3 = adj for lt1764 *pin 5 = sense for lt1764-1.5/lt1764-1.8/ lt1764-2.5/lt1764-3.3 = adj for lt1764 t jmax = 150 c, ja = 50 c/ w q package 5-lead plastic dd tab is gnd front view sense/adj*out gnd in shdn 54 3 2 1 t package 5-lead plastic to-220 sense/adj* out gnd in shdn front view tab is gnd 54 3 2 1 lt1764efelt1764efe-1.5 lt1764efe-1.8 lt1764efe-2.5 lt1764efe-3.3 order part number fe package 16-lead plastic tssop exposed pad (pin 17) is gnd. must be soldered to the pcb. 12 3 4 5 6 7 8 top view 1615 14 13 12 11 10 9 gnd nc outout out sense/adj* gndgnd gndnc in in in nc shdn gnd 17 t jmax = 150 c, ja = 38 c/ w *pin 6 = sense for lt1764-1.5/ lt1764-1.8/lt1764-2.5/lt1764-3.3 = adj for lt1764 1764efe1764efe15 1764efe18 1764efe25 1764efe33 fe part marking downloaded from: http:///
3 lt1764 series 1764fb parameter conditions min typ max units minimum input voltage i load = 0.5a 1.7 v (notes 3, 11) i load = 1.5a 1.9 v i load = 2.7a, 110 c < t j 125 c 2.3 2.7 v i load = 3a, 40 c t j 110 c 2.3 2.7 v regulated output voltage lt1764-1.5 v in = 2.21v, i load = 1ma 1.477 1.500 1.523 v (note 4) 2.7v < v in < 20v, 1ma < i load < 3a, 40 c t j 110 c 1.447 1.500 1.545 v 2.7v < v in < 20v, 1ma < i load < 2.7a, 110 c < t j 125 c 1.447 1.500 1.545 v lt1764-1.8 v in = 2.3v, i load = 1ma 1.773 1.800 1.827 v 2.8v < v in < 20v, 1ma < i load < 3a, 40 c t j 110 c 1.737 1.800 1.854 v 2.8v < v in < 20v, 1ma < i load < 2.7a, 110 c < t j 125 c 1.737 1.800 1.854 v lt1764-2.5 v in = 3v, i load = 1ma 2.462 2.500 2.538 v 3.5v < v in < 20v, 1ma < i load < 3a, 40 c t j 110 c 2.412 2.500 2.575 v 3.5v < v in < 20v, 1ma < i load < 2.7a, 110 c < t j 125 c 2.412 2.500 2.575 v lt1764-3.3 v in = 3.8v, i load = 1ma 3.250 3.300 3.350 v 4.3v < v in < 20v, 1ma < i load < 3a, 40 c t j 110 c 3.183 3.300 3.400 v 4.3v < v in < 20v, 1ma < i load < 2.7a, 110 c < t j 125 c 3.183 3.300 3.400 v adj pin voltage lt1764 v in = 2.21v, i load = 1ma 1.192 1.210 1.228 v (notes 3, 4) 2.7v < v in < 20v, 1ma < i load < 3a, 40 c t j 110 c 1.168 1.210 1.246 v 2.7v < v in < 20v, 1ma < i load < 2.7a, 110 c < t j 125 c 1.168 1.210 1.246 v line regulation lt1764-1.5 ? v in = 2.21v to 20v, i load = 1ma 2.5 10 mv lt1764-1.8 ? v in = 2.3v to 20v, i load = 1ma 31 0m v lt1764-2.5 ? v in = 3v to 20v, i load = 1ma 41 0m v lt1764-3.3 ? v in = 3.8v to 20v, i load = 1ma 4.5 10 mv lt1764 (note 3) ? v in = 2.21v to 20v, i load = 1ma 21 0m v load regulation lt1764-1.5 v in = 2.7v, ? i load = 1ma to 3a 3 7 mv v in = 2.7v, ? i load = 1ma to 3a, 40 c t j 110 c2 3 m v v in = 2.7v, ? i load = 1ma to 2.7a, 110 c < t j 125 c2 3 m v lt1764-1.8 v in = 2.8v, ? i load = 1ma to 3a 4 8 mv v in = 2.8v, ? i load = 1ma to 3a, 40 c t j 110 c2 5 m v v in = 2.8v, ? i load = 1ma to 2.7a, 110 c < t j 125 c2 5 m v lt1764-2.5 v in = 3.5v, ? i load = 1ma to 3a 4 10 mv v in = 3.5v, ? i load = 1ma to 3a, 40 c t j 110 c3 0 m v v in = 3.5v, ? i load = 1ma to 2.7a, 110 c < t j 125 c3 0 m v lt1764-3.3 v in = 4.3v, ? i load = 1ma to 3a 4 12 mv v in = 4.3v, ? i load = 1ma to 3a, 40 c t j 110 c4 0 m v v in = 4.3v, ? i load = 1ma to 2.7a, 110 c < t j 125 c4 0 m v lt1764 (note 3) v in = 2.7v, ? i load = 1ma to 3a 2 5 mv v in = 2.7v, ? i load = 1ma to 3a, 40 c t j 110 c2 0 m v v in = 2.7v, ? i load = 1ma to 2.7a, 110 c < t j 125 c2 0 m v dropout voltage i load = 1ma 0.02 0.05 v v in = v out(nominal) i load = 1ma 0.10 v (notes 5, 6, 11) i load = 100ma 0.07 0.13 v i load = 100ma 0.18 v i load = 500ma 0.14 0.20 v i load = 500ma 0.27 v i load = 1.5a 0.25 0.33 v i load = 1.5a 0.40 v i load = 2.7a, 110 c < t j 125 c 0.66 v i load = 3a 0.34 0.45 v i load = 3a, 40 c t j 110 c 0.66 v electrical characteristics the denotes specifications which apply over the full operating temperature range, otherwise specifications are t a = 25 c. (note 2) downloaded from: http:///
4 lt1764 series 1764fb gnd pin current i load = 0ma 1 1.5 ma v in = v out(nominal) + 1v i load = 1ma 1.1 1.6 ma (notes 5, 7) i load = 100ma 3.5 5 ma i load = 500ma 11 18 ma i load = 1.5a 40 75 ma i load = 2.7a, 110 c < t j 125 c 120 200 ma i load = 3a, 40 c t j 110 c 120 200 ma output voltage noise c out = 10 f, i load = 3a, bw = 10hz to 100khz 40 v rms adj pin bias current (notes 3, 8) 31 0 a shutdown threshold v out = off to on 0.9 2 v v out = on to off 0.25 0.75 v shdn pin current v shdn = 0v 0.01 1 a (note 9) v shdn = 20v 7 30 a quiescent current in shutdown v in = 6v, v shdn = 0v 0.01 1 a ripple rejection v in ?v out = 1.5v (avg), v ripple = 0.5v p-p ,5 5 6 3 d b f ripple = 120hz, i load = 1.5a current limit v in = 7v, v out = 0v 4 a lt1764-1.8, lt1764-2.5, lt1764-3.3v in = v out(nominal) + 1v, ? v out = 0.1v, 40 c t j 110 c 3.1 a v in = v out(nominal) + 1v, ? v out = 0.1v, 110 c < t j 125 c 2.8 a lt1764, lt1764-1.5v in = 2.7v, ? v out = 0.1v, 40 c t j 110 c 3.1 a v in = 2.7v, ? v out = 0.1v, 110 c < t j 125 c 2.8 a input reverse leakage current v in = 20v, v out = 0v 1m a reverse output current (note 10) lt1764-1.5 v out = 1.5v, v in < 1.5v 600 1200 a lt1764-1.8 v out = 1.8v, v in < 1.8v 600 1200 a lt1764-2.5 v out = 2.5v, v in < 2.5v 600 1200 a lt1764-3.3 v out = 3.3v, v in < 3.3v 600 1200 a lt1764 (note 3) v out = 1.21v, v in < 1.21v 300 600 a note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolutemaximum rating condition for extended periods may affect device reliability and lifetime. note 2: the lt1764 regulators are tested and specified under pulse load conditions such that t j t a . the lt1764 is 100% tested at t a = 25 c. performance at 40 c and 125 c is assured by design, characterization and correlation with statistical process controls.note 3: the lt1764 (adjustable version) is tested and specified for these conditions with the adj pin connected to the out pin.note 4. operating conditions are limited by maximum junction temperature. the regulated output voltage specification will not apply forall possible combinations of input voltage and output current. when operating at maximum input voltage, the output current range must be limited. when operating at maximum output current, the input voltage range must be limited. note 5: to satisfy requirements for minimum input voltage, the lt1764 (adjustable version) is tested and specified for these conditions with anexternal resistor divider (two 4.12k resistors) for an output voltage of 2.42v. the external resistor divider will add a 300 a dc load on the output. note 6: dropout voltage is the minimum input to output voltage differential needed to maintain regulation at a specified output current. in dropout, theoutput voltage will be equal to: v in ?v dropout . note 7: gnd pin current is tested with v in = v out(nominal) + 1v or v in = 2.7v (whichever is greater) and a current source load. the gnd pin current will decrease at higher input voltages.note 8: adj pin bias current flows into the adj pin. note 9: shdn pin current flows into the shdn pin. note 10: reverse output current is tested with the in pin grounded and the out pin forced to the rated output voltage. this current flows into the outpin and out the gnd pin. note 11. for the lt1764, lt1764-1.5 and lt1764-1.8 dropout voltage will be limited by the minimum input voltage specification under some outputvoltage/load conditions. note 12. all combinations of absolute maximum input voltage and absolute maximum output voltage cannot be achieved. the absolutemaximum differential from input to output is 20v. for example, with v in = 20v, v out cannot be pulled below ground. electrical characteristics parameter conditions min typ max units the denotes specifications which apply over the full operating temperature range, otherwise specifications are t a = 25 c. (note 2) downloaded from: http:///
5 lt1764 series 1764fb temperature ( c) ?0 0.8 1.0 1.4 25 75 1764 g04 0.60.4 ?5 0 50 100 125 0.2 0 1.2 quiescent current (ma) lt1764-1.8/2.5/3.3 lt1764 v in = 6v r l = i l = 0 v shdn = v in temperature ( c) ?0 output voltage (v) 25 1756 g05 ?5 0 50 1.841.83 1.82 1.81 1.80 1.79 1.78 1.77 1.76 75 100 125 i l = 1ma temperature ( c) ?0 output voltage (v) 25 1756 g06 ?5 0 50 2.582.56 2.54 2.52 2.50 2.48 2.46 2.44 2.42 75 100 125 i l = 1ma output current (a) 0 0 dropout voltage (mv) 100 200 300 400 600 0.5 1.0 1.5 2.0 1764 g01 2.5 3.0 500 t j = 125 c t j = 25 c output current (a) 0 700600 500 400 300 200 100 0 1.5 2.5 1764 g02 0.5 1.0 2.0 3.0 guaranteed dropout voltage (mv) = test points t j 125 c t j 25 c temperature ( c) ?0 dropout voltage (mv) 400 500 600 25 75 1764 g03 300 200 ?5 0 50 100 125 100 0 i l = 3a i l = 1.5a i l = 0.5a i l = 100ma i l = 1ma typical perfor a ce characteristics uw quiescent current lt1764-1.8 output voltage lt1764-2.5 output voltage lt1764-3.3 output voltage lt1764 adj pin voltage lt1764-1.8 quiescent current temperature ( c) ?0 output voltage (v) 25 1756 g07 ?5 0 50 3.383.36 3.34 3.32 3.30 3.28 3.26 3.24 3.22 75 100 125 i l = 1ma temperature ( c) ?0 adj pin voltage (v) 25 1756 g08 ?5 0 50 1.2301.225 1.220 1.215 1.210 1.205 1.200 1.195 1.190 75 100 125 i l = 1ma input voltage (v) 0 quiescent current (ma) 4035 30 25 20 15 10 50 8 1764 g09 246 1 0 7 135 9 t j = 25 c r l = v shdn = v in typical dropout voltage guaranteed dropout voltage dropout voltage downloaded from: http:///
6 lt1764 series 1764fb input voltage (v) 0 gnd pin current (ma) 9 12 15 8 1764 g16 6 3 0 2 4 6 19 3 5 7 10 r l = 2.42 ? i l = 500ma* r l = 12.1 ? i l = 100ma* r l = 4.33 ? i l = 300ma* t j = 25 c v shdn = v in *for v out = 1.21v input voltage (v) 0 gnd pin current (ma) 90 120 150 8 1764 g17 60 30 0 2 4 6 19 3 5 7 10 r l = 0.6 ? i l = 3a* r l = 2.57 ? i l = 0.7a* r l = 1.2 ? i l = 1.5a* t j = 25 c v shdn = v in *for v out = 1.8v input voltage (v) 0 gnd pin current (ma) 120 160 200 8 1764 g18 80 40 0 2 4 6 19 3 5 7 10 r l = 0.83 ? i l = 3a* r l = 3.57 ? i l = 0.7a* r l = 1.66 ? i l = 1.5a* t j = 25 c v shdn = v in *for v out = 2.5v typical perfor a ce characteristics uw lt1764-1.8 gnd pin current lt1764-2.5 gnd pin current lt1764-3.3 gnd pin current lt1764 gnd pin current lt1764-1.8 gnd pin current lt1764-2.5 gnd pin current input voltage (v) 1 0 gnd pin current (ma) 20.017.5 15.0 12.5 10.0 7.55.0 2.5 0 9 1764 g13 3578 246 1 0 t j = 25 c v shdn = v in *for v out = 1.8v r l = 3.6 ? i l = 500ma* r l = 18 ? i l = 100ma* r l = 6 ? i l = 300ma* input voltage (v) 1 0 gnd pin current (ma) 4035 30 25 20 15 10 50 9 1764 g14 3578 246 1 0 t j = 25 c v shdn = v in *for v out = 2.5v r l = 5 ? i l = 500ma* r l = 25 ? i l = 100ma* r l = 8.33 ? i l = 300ma* input voltage (v) 1 0 gnd pin current (ma) 8070 60 50 40 30 20 10 0 9 1764 g15 3578 246 1 0 t j = 25 c v shdn = v in *for v out = 3.3v r l = 6.6 ? i l = 500ma* r l = 33 ? i l = 100ma* r l = 11 ? i l = 300ma* lt1764-2.5 quiescent current lt1764-3.3 quiescent current lt1764 quiescent current input voltage (v) 0 quiescent current (ma) 4035 30 25 20 15 10 50 8 1764 g10 246 1 0 7 135 9 t j = 25 c r l = v shdn = v in input voltage (v) 0 quiescent current (ma) 4035 30 25 20 15 10 50 8 1764 g11 246 1 0 7 135 9 t j = 25 c r l = v shdn = v in input voltage (v) 0 quiescent current (ma) 1.61.4 1.2 1.0 0.8 0.6 0.4 0.2 0 16 1764 g12 4 8 12 20 14 2 6 10 18 t j = 25 c r l = 4.3k v shdn = v in downloaded from: http:///
7 lt1764 series 1764fb typical perfor a ce characteristics uw shdn pin input current adj pin bias current current limit temperature ( c) ?0 0 shdn pin threshold (v) 0.1 0.3 0.4 0.5 1.00.7 0 50 75 1764 g22 0.2 0.8 0.90.6 ?5 25 100 125 i l = 1ma temperature ( c) ?0 0 shdn pin threshold (v) 0.1 0.3 0.4 0.5 1.00.7 0 50 75 1764 g23 0.2 0.8 0.90.6 ?5 25 100 125 i l = 3a i l = 1ma shdn pin voltage (v) 0 shdn pin input current ( a) 6 8 10 16 1764 g24 42 5 7 93 1 0 4 8 12 21 8 6 10 14 20 temperature ( c) ?0 0 shdn pin input current ( a) 1 3 4 5 10 7 0 50 75 1764 g25 2 8 96 ?5 25 100 125 v shdn = 20v temperature ( c) ?0 adj pin bias current ( a) 25 1756 g26 ?5 0 50 4.03.5 3.0 2.5 2.0 1.5 1.0 0.5 0 75 100 125 input/output differential (v) 0 current limit (a) 2 4 61 3 5 4 8 12 16 1764 g27 20 2 0 6 10 14 18 t j = 50 c t j = 125 c t j = 25 c lt1764-3.3 gnd pin current lt1764 gnd pin current gnd pin current vs i load input voltage (v) 0 gnd pin current (ma) 120 160 200 8 1764 g19 80 40 0 2 4 6 19 3 5 7 10 r l = 1.1 ? i l = 3a* r l = 2.2 ? i l = 1.5a* t j = 25 c v shdn = v in *for v out = 3.3v r l = 4.71 ? i l = 0.7a* input voltage (v) 0 gnd pin current (ma) 90 120 150 8 1764 g20 60 30 0 2 4 6 19 3 5 7 10 r l = 0.4 ? i l = 3a* r l = 0.81 ? i l = 1.5a* t j = 25 c v shdn = v in *for v out = 1.21v r l = 1.73 ? i l = 0.7a* output current (a) 0 gnd pin current (ma) 60 80 100 1.5 2.5 1764 g21 40 20 0 0.5 1.0 2.0 120 140 160 3.0 v in = v out(nom) + 1v shdn pin threshold(off-to-on) shdn pin input current shdn pin threshold(on-to-off) downloaded from: http:///
8 lt1764 series 1764fb typical perfor a ce characteristics uw ripple rejection ripple rejection lt1764 minimum input voltage frequency (hz) 20 ripple rejection (db) 30 50 70 80 10 1k 10k 1m 1764 g31 10 100 100k 6040 0 c out = 100 f tantalum + 10 1 f ceramic c out = 10 f tantalum i l = 1.5a v in = v out(nom) + 1v + 50mv rms ripple temperature ( c) 50 ?5 50 ripple rejection (db) 60 75 0 50 75 1764 g32 55 70 65 25 100 125 i l = 1.5a v in = v out(nom) + 1v + 0.5v p-p ripple at f = 120hz temperature ( c) ?0 minimum input voltage (v) 2.0 2.5 3.0 25 75 1764 g33 1.5 1.0 ?5 0 50 100 125 0.5 0 i l = 3a i l = 1.5a i l = 100ma i l = 500ma current limit reverse output current reverse output current temperature ( c) ?0 current limit (a) 4 5 6 25 75 1764 g28 3 2 ?5 0 50 100 125 1 0 v in = 7v v out = 0v output voltage (v) 0 reverse output current (ma) 3.0 4.0 5.0 8 1764 g29 2.01.0 2.5 3.5 4.51.5 0.5 0 2 4 6 19 3 5 7 10 t j = 25 c v in = 0v current flows into output pin v out = v adj (lt1764) v out = v fb (lt1764-1.8/-2.5/-3.3) lt1764 lt1764-1.8 lt1764-2.5 lt1764-3.3 temperature ( c) ?0 0 reverse output current (ma) 0.1 0.3 0.4 0.5 1.00.7 0 50 75 1764 g30 0.2 0.8 0.90.6 ?5 25 100 125 v in = 0v v out = 1.21v (lt1764) v out = 1.8v (lt1764-1.8) v out = 2.5v (lt1764-2.5) v out = 3.3v (lt1764-3.3) lt1764-1.8/-2.5/-3.3 lt1764 downloaded from: http:///
9 lt1764 series 1764fb lt1764-3.3 10hz to 100khzoutput noise lt1764-3.3 transient response temperature ( c) ?0 load regulation (mv) 25 1764 g34 ?5 0 50 10 50 ? ?0 ?5 ?0 ?5 ?0 75 100 125 lt1764 lt1764-3.3 lt1764-2.5 lt1764-1.8 ? i l = 1ma to 3a v in = 2.7v (lt1764) v in = v out(nom) + 1v (lt1764-1.8/-2.5/-3.3) frequency (hz) 10 0.01 output noise spectral density ( v/ hz) 0.1 1 100 1k 10k 100k 1764 g35 lt1764-3.3 lt1764-2.5 lt1764-1.8 lt1764 c out = 10 f i load = 3a load current (a) 10 output noise ( v rms ) 15 25 35 40 0.0001 0.01 0.1 10 1764 g36 5 0.001 1 3020 0 lt1764-3.3 lt1764-2.5 lt1764-1.8 lt1764 c out = 10 f v out 100 v/ div c out = 10 f 1ms/div 1764 g37 i l = 3a time ( s) 0 output voltage deviation (v) load current (a) 0.1 0.1 0.2 0 0.2 16 1764 g38 1.000.50 0.750.25 0 46 2 8 12 14 18 10 20 v in = 4.3v c in = 3.3 f tantalum c out = 10 f tantalum lt1764-3.3 transient response time ( s) 0 output voltage deviation (v) load current (a) 0.1 0.1 0.2 0 0.2 16 1764 g39 2 31 0 46 2 8 12 14 18 10 20 v in = 4.3v c in = 33 f c out = 100 f tantalum + 10 1 f ceramic typical perfor a ce characteristics uw load regulation output noise spectral density rms output noise vs load current(10hz to 100khz) downloaded from: http:///
10 lt1764 series 1764fb out (pin 4/pins 3, 4, 5): output. the output supplies power to the load. a minimum output capacitor of 10 f is required to prevent oscillations. larger output capacitorswill be required for applications with large transient loads to limit peak voltage transients. see the applications information section for more information on output ca- pacitance and reverse output characteristics. sense (pin 5/pin 6): sense. for fixed voltage versions of the lt1764 (lt1764-1.8/lt1764-2.5/lt1764-3.3), thesense pin is the input to the error amplifier. optimum regulation will be obtained at the point where the sense pin is connected to the out pin of the regulator. in critical applications, small voltage drops are caused by the resis- tance (r p ) of pc traces between the regulator and the load. these may be eliminated by connecting the sense pin tothe output at the load as shown in figure 1 (kelvin sense connection). note that the voltage drop across the exter- nal pc traces will add to the dropout voltage of the regulator. the sense pin bias current is 600 a at the nominal rated output voltage. the sense pin can be pulledbelow ground (as in a dual supply system where the regulator load is returned to a negative supply) and still allow the device to start and operate. adj (pin 5/pin 6): adjust. for the adjustable lt1764, this is the input to the error amplifier. this pin is internallyclamped to 7v. it has a bias current of 3 a which flows into the pin. the adj pin voltage is 1.21v referenced toground and the output voltage range is 1.21v to 20v. shdn (pin 1/pin 10): shutdown. the shdn pin is used to put the lt1764 regulators into a low power shutdownstate. the output will be off when the shdn pin is pulled low. the shdn pin can be driven either by 5v logic or open-collector logic with a pull-up resistor. the pull-up resistor is required to supply the pull-up current of the open-collector gate, normally several microamperes, and the shdn pin current, typically 7 a. if unused, the shdn pin must be connected to v in . the device will be in the low power shutdown state if the shdn pin is not connected.in (pin 2/pins 12, 13, 14): input. power is supplied to the device through the in pin. a bypass capacitor is requiredon this pin if the device is more than six inches away from the main input filter capacitor. in general, the output impedance of a battery rises with frequency, so it is advisable to include a bypass capacitor in battery-pow- ered circuits. a bypass capacitor in the range of 1 f to 10 f is sufficient. the lt1764 regulators are designed to withstand reverse voltages on the in pin with respect toground and the out pin. in the case of a reverse input, which can happen if a battery is plugged in backwards, the device will act as if there is a diode in series with its input. there will be no reverse current flow into the regulator and no reverse voltage will appear at the load. the device will protect both itself and the load. gnd (pin 3/pins 1, 7, 8, 9, 16, 17): ground. the exposed pad (fe package) is ground and must be soldered to thepcb for rated thermal performance. figure 1. kelvin sense connection inshdn 1764 f01 r p out v in sense gnd lt1764 r p 3 5 4 1 2 + + load uu u pi fu ctio s (dd and to-220/tssop) downloaded from: http:///
11 lt1764 series 1764fb the lt1764 series are 3a low dropout regulators opti-mized for fast transient response. the devices are capable of supplying 3a at a dropout voltage of 340mv. the low operating quiescent current (1ma) drops to less than 1 a in shutdown. in addition to the low quiescent current, thelt1764 regulators incorporate several protection features which make them ideal for use in battery-powered sys- tems. the devices are protected against both reverse input and reverse output voltages. in battery backup applica- tions where the output can be held up by a backup battery when the input is pulled to ground, the lt1764-x acts like it has a diode in series with its output and prevents reverse current flow. additionally, in dual supply applications where the regulator load is returned to a negative supply, the output can be pulled below ground by as much as 20v and still allow the device to start and operate. adjustable operation the adjustable version of the lt1764 has an output voltage range of 1.21v to 20v. the output voltage is set by the ratio of two external resistors as shown in figure 2. the device servos the output to maintain the voltage at the adj pin at 1.21v referenced to ground. the current in r1 is then equal to 1.21v/r1 and the current in r2 is the current in r1 plus the adj pin bias current. the adj pin bias current, 3 a at 25 c, flows through r2 into the adj pin. the output voltage can be calculated using the formula infigure 2. the value of r1 should be less than 4.17k to minimize errors in the output voltage caused by the adj pin bias current. note that in shutdown the output is turned off and the divider current will be zero. the adjustable device is tested and specified with the adj pin tied to the out pin for an output voltage of 1.21v. specifications for output voltages greater than 1.21v will figure 2. adjustable operation be proportional to the ratio of the desired output voltage to1.21v: v out /1.21v. for example, load regulation for an output current change of 1ma to 3a is 3mv typical at v out = 1.21v. at v out = 5v, load regulation is: (5v/1.21v)(?mv) = 12.4mv output capacitance and transient responsethe lt1764 regulators are designed to be stable with a wide range of output capacitors. the esr of the output capacitor affects stability, most notably with small capaci- tors. a minimum output capacitor of 10 f with an esr in the range of 50m ? to 3 ? is recommended to prevent oscillations. larger values of output capacitance can de-crease the peak deviations and provide improved transi- ent response for larger load current changes. bypass capacitors, used to decouple individual components pow- ered by the lt1764-x, will increase the effective output capacitor value. extra consideration must be given to the use of ceramic capacitors. ceramic capacitors are manufactured with a variety of dielectrics, each with different behavior across temperature and applied voltage. the most common di- electrics used are specified with eia temperature charac- teristic codes of z5u, y5v, x5r and x7r. the z5u and y5v dielectrics are good for providing high capacitances in a small package, but they tend to have strong voltage and temperature coefficients as shown in figures 3 and 4. when used with a 5v regulator, a 16v 10 f y5v capacitor can exhibit an effective value as low as 1 f to 2 f for the dc bias voltage applied and over the operating tempera-ture range. the x5r and x7r dielectrics result in more stable characteristics and are more suitable for use as the output capacitor. the x7r type has better stability across temperature, while the x5r is less expensive and is available in higher values. care still must be exercised when using x5r and x7r capacitors; the x5r and x7r codes only specify operating temperature range and maxi- mum capacitance change over temperature. capacitance change due to dc bias with x5r and x7r capacitors is better than y5v and z5u capacitors, but can still be significant enough to drop capacitor values below appro- priate levels. capacitor dc bias characteristics tend to improve as component case size increases, but expected capacitance at operating voltage should be verified. in 1764 f02 r2 out v in v out adj gnd lt1764 r1 + vv r r ir vv ia out adj adj adj =+ ? ? ? ? ? ? + () () = = 121 1 2 1 2 121 3 . . at 25 c output range = 1.21v to 20v applicatio s i for atio wu uu downloaded from: http:///
12 lt1764 series 1764fb figure 4. ceramic capacitor temperature characteristics the protection is designed to provide some output currentat all values of input-to-output voltage up to the device breakdown. when power is first turned on, as the input voltage rises, the output follows the input, allowing the regulator to start up into very heavy loads. during the start-up, as the input voltage is rising, the input-to-output voltage differential is small, allowing the regulator to supply large output cur- rents. with a high input voltage, a problem can occur wherein removal of an output short will not allow the output voltage to recover. other regulators, such as the lt1085, also exhibit this phenomenon, so it is not unique to the lt1764 series. the problem occurs with a heavy output load when the input voltage is high and the output voltage is low. com- mon situations are immediately after the removal of a short circuit or when the shdn pin is pulled high after the input voltage has already been turned on. the load line for such a load may intersect the output current curve at two points. if this happens, there are two stable output oper- ating points for the regulator. with this double intersec- tion, the input power supply may need to be cycled down to zero and brought up again to make the output recover. output voltage noise the lt1764 regulators have been designed to provide low output voltage noise over the 10hz to 100khz bandwidth while operating at full load. output voltage noise is typi- cally 50nv hz over this frequency bandwidth for the lt1764 (adjustable version). for higher output voltages(generated by using a resistor divider), the output voltage noise will be gained up accordingly. this results in rms noise over the 10hz to 100khz bandwidth of 15 v rms for the lt1764 increasing to 37 v rms for the lt1764-3.3. higher values of output voltage noise may be measuredwhen care is not exercised with regards to circuit layout and testing. crosstalk from nearby traces can induce unwanted noise onto the output of the lt1764-x. power supply ripple rejection must also be considered; the lt1764 regulators do not have unlimited power supply rejection and will pass a small portion of the input noise through to the output. temperature ( c) ?0 4020 0 ?0 ?0 ?0 ?0 100 25 75 1764 f04 ?5 0 50 100 125 y5v change in value (%) x5r both capacitors are 16v,1210 case size, 10 f applicatio s i for atio wu uu figure 3. ceramic capacitor dc bias characteristics dc bias voltage (v) change in value (%) 1764 f03 20 0 ?0 ?0 ?0 ?0 100 0 4 8 10 26 12 14 x5r y5v 16 both capacitors are 16v,1210 case size, 10 f voltage and temperature coefficients are not the onlysources of problems. some ceramic capacitors have a piezoelectric response. a piezoelectric device generates voltage across its terminals due to mechanical stress, similar to the way a piezoelectric accelerometer or micro- phone works. for a ceramic capacitor the stress can be induced by vibrations in the system or thermal transients. overload recovery like many ic power regulators, the lt1764-x has safe operating area protection. the safe area protection de- creases the current limit as input-to-output voltage in- creases and keeps the power transistor inside a safe operating region for all values of input-to-output voltage. downloaded from: http:///
13 lt1764 series 1764fb applicatio n s i n for m atio n wu u u thermal considerationsthe power handling capability of the device is limited by the maximum rated junction temperature (125 c). the power dissipated by the device is made up of twocomponents: 1. output current multiplied by the input/output voltage differential: (i out )(v in ?v out ), and 2. gnd pin current multiplied by the input voltage: (i gnd )(v in ). the gnd pin current can be found using the gnd pincurrent curves in the typical performance characteris- tics. power dissipation will be equal to the sum of the two components listed above. the lt1764 series regulators have internal thermal limit- ing designed to protect the device during overload condi- tions. for continuous normal conditions, the maximum junction temperature rating of 125 c must not be exceeded. it is important to give careful consideration toall sources of thermal resistance from junction to ambient. additional heat sources mounted nearby must also be considered. for surface mount devices, heat sinking is accomplished by using the heat spreading capabilities of the pc board and its copper traces. surface mount heatsinks and plated through-holes can also be used to spread the heat gener- ated by power devices. the following tables list thermal resistance for several different board sizes and copper areas. all measurements were taken in still air on 1/16" fr-4 board with one ounce copper. table 1. q package, 5-lead dd copper area thermal resistance topside* backside board area (junction-to-ambient) 2500mm 2 2500mm 2 2500mm 2 23 c/w 1000mm 2 2500mm 2 2500mm 2 25 c/w 125mm 2 2500mm 2 2500mm 2 33 c/w table 2. fe package, 16-lead tssop copper area thermal resistance topside* backside board area (junction-to-ambient) 2500mm 2 2500mm 2 2500mm 2 38 c/w 1000mm 2 2500mm 2 2500mm 2 43 c/w 225mm 2 2500mm 2 2500mm 2 48 c/w 100mm 2 2500mm 2 2500mm 2 60 c/w t package, 5-lead to-220thermal resistance (junction-to-case) = 2.5 c/w calculating junction temperatureexample: given an output voltage of 3.3v, an input voltage range of 4v to 6v, an output current range of 0ma to 500ma and a maximum ambient temperature of 50 c, what will the maximum junction temperature be?the power dissipated by the device will be equal to: i out(max) (v in(max) ?v out ) + i gnd (v in(max) ) where, i out(max) = 500ma v in(max) = 6v i gnd at (i out = 500ma, v in = 6v) = 10ma so, p = 500ma(6v ?3.3v) + 10ma(6v) = 1.41w using a dd package, the thermal resistance will be in therange of 23 c/w to 33 c/w depending on the copper area. so the junction temperature rise above ambient willbe approximately equal to: 1.41w(28 c/w) = 39.5 c the maximum junction temperature will then be equal tothe maximum junction temperature rise above ambient plus the maximum ambient temperature or: t jmax = 50 c + 39.5 c = 89.5 c * device is mounted on topside * device is mounted on topside downloaded from: http:///
14 lt1764 series 1764fb protection featuresthe lt1764 regulators incorporate several protection features which make them ideal for use in battery-powered circuits. in addition to the normal protection features associated with monolithic regulators, such as current limiting and thermal limiting, the devices are protected against reverse input voltages, reverse output voltages and reverse voltages from output to input. current limit protection and thermal overload protection are intended to protect the device against current overload conditions at the output of the device. for normal opera- tion, the junction temperature should not exceed 125 c. the input of the device will withstand reverse voltages of20v. current flow into the device will be limited to less than 1ma and no negative voltage will appear at the output. the device will protect both itself and the load. this provides protection against batteries which can be plugged in backward. the output of the lt1764-x can be pulled below ground without damaging the device. if the input is left open circuit or grounded, the output can be pulled below ground by 20v. for fixed voltage versions, the output will act like a large resistor, typically 5k or higher, limiting current flow to typically less than 600 a. for adjustable versions, the output will act like an open circuit; no current will flow outof the pin. if the input is powered by a voltage source, the output will source the short-circuit current of the device and will protect itself by thermal limiting. in this case, grounding the shdn pin will turn off the device and stop the output from sourcing the short-circuit current. the adj pin of the adjustable device can be pulled aboveor below ground by as much as 7v without damaging the device. if the input is left open circuit or grounded, the adj pin will act like an open circuit when pulled below ground and like a large resistor (typically 5k) in series with a diode when pulled above ground. in situations where the adj pin is connected to a resistor divider that would pull the adj pin above its 7v clamp voltage if the output is pulled high, the adj pin input current must be limited to less than 5ma. for example, a resistor divider is used to provide a regulated 1.5v output from the 1.21v reference when the output is forced to 20v. the top resistor of the resistor divider must be chosen to limit the current into the adj pin to less than 5ma when the adj pin is at 7v. the 13v difference between out and adj pins divided by the 5ma maximum current into the adj pin yields a minimum top resistor value of 2.6k. in circuits where a backup battery is required, several different input/output conditions can occur. the output voltage may be held up while the input is either pulled to ground, pulled to some intermediate voltage, or is left open circuit. current flow back into the output will follow the curve shown in figure 5. when the in pin of the lt1764-x is forced below the out pin or the out pin is pulled above the in pin, input current will typically drop to less than 2 a. this can happen if the input of the device is connected to a discharged (lowvoltage) battery and the output is held up by either a backup battery or a second regulator circuit. the state of the shdn pin will have no effect on the reverse output current when the output is pulled above the input. applicatio n s i n for m atio n wu u u figure 5. reverse output current output voltage (v) 012345678910 reverse output current (ma) 1764 f05 5.04.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 lt1764-2.5 lt1764-3.3 lt1764-1.8 lt1764 t j = 25 c v in = ov current flows into output pin v out = v adj (lt1764) v out = v fb (lt1764-1.8, lt1764-2.5, lt1764-3.3) downloaded from: http:///
15 lt1764 series 1764fb typical applicatio s u + a1 lt1006 + c1b 1/2 lt1018 + c1a 1/2 lt1018 lt10041.2v 1764 ta03 1 f 1n4148 1n4148 10k 10k 750 ? 750 ? 2.4k 22 f 1n4002 to all ? + points 200k 34k* 12.1k* 0.1 f v + v + v + v + 10k v + 0.033 f + 10000 f + 22 f v out 3.3v3a + 1n4002 1n4002 1k 10v acat 115v in 1n4148 l1 500 h 90v ac to 140v ac 10v acat 115v in lt1764-3.3 gnd inshdn out fb l1: coiltronics ctx500-2-52l2: stancor p-8560 *1% film resistor nte5437 l2 nte5437 ?ync scr preregulator provides efficiency over line variations downloaded from: http:///
16 lt1764 series 1764fb typical applicatio s u adjustable current source lt1764-1.8 gnd inshdn r8100k out fb + r7470 ? 4 8 1764 ta04 c23.3 f c3 1 f r1 1k r32k c110 f v in > 2.7v lt1004-1.2 r5 0.01 ? r2 40.2k r42.2k 23 1 r62.2k + load 1/2 lt1366 adjust r1 for 0a to 3a constant current downloaded from: http:///
17 lt1764 series 1764fb package descriptio n u q package 5-lead plastic dd pak (ltc dwg # 05-08-1461) q(dd5) 0502 .028 ?.038 (0.711 ?0.965) typ .143 +.012?020 () 3.632 +0.305 0.508 .067 (1.702) bsc .013 ?.023 (0.330 ?0.584) .095 ?.115 (2.413 ?2.921) .004 +.008?004 () 0.102 +0.203 0.102 .050 .012 (1.270 0.305) .059 (1.499) typ .045 ?.055 (1.143 ?1.397) .165 ?.180 (4.191 ?4.572) .330 ?.370 (8.382 ?9.398) .060 (1.524) typ .390 ?.415 (9.906 ?10.541) 15 typ .420 .350 .565 .090 .042 .067 recommended solder pad layout .325 .205 .080 .565 .090 recommended solder pad layout for thicker solder paste applications .042 .067 .420 .276 .320 note:1. dimensions in inch/(millimeter) 2. drawing not to scale .300 (7.620) .075 (1.905) .183 (4.648) .060 (1.524) .060 (1.524) .256 (6.502) bottom view of dd pak hatched area is solder plated copper heat sink downloaded from: http:///
18 lt1764 series 1764fb package descriptio n u t5 (to-220) 0399 0.028 ?0.038 (0.711 ?0.965) 0.067 (1.70) 0.135 ?0.165 (3.429 ?4.191) 0.700 ?0.728 (17.78 ?18.491) 0.045 ?0.055 (1.143 ?1.397) 0.095 ?0.115 (2.413 ?2.921) 0.013 ?0.023 (0.330 ?0.584) 0.620 (15.75) typ 0.155 ?0.195* (3.937 ?4.953) 0.152 ?0.202 (3.861 ?5.131) 0.260 ?0.320 (6.60 ?8.13) 0.165 ?0.180 (4.191 ?4.572) 0.147 ?0.155 (3.734 ?3.937) dia 0.390 ?0.415 (9.906 ?10.541) 0.330 ?0.370 (8.382 ?9.398) 0.460 ?0.500 (11.684 ?12.700) 0.570 ?0.620 (14.478 ?15.748) 0.230 ?0.270 (5.842 ?6.858) bsc seating plane * measured at the seating plane t package 5-lead plastic to-220 (standard) (ltc dwg # 05-08-1421) downloaded from: http:///
19 lt1764 series 1764fb fe package 16-lead plastic tssop (4.4mm) (reference ltc dwg # 05-08-1663) exposed pad variation bb 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 represen-tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. package descriptio n u fe16 (bb) tssop 0204 0.09 ?0.20 (.0035 ?.0079) 0 ?8 0.25 ref 0.50 ?0.75 (.020 ?.030) 4.30 ?4.50* (.169 ?.177) 134 5 6 7 8 10 9 4.90 ?5.10* (.193 ?.201) 16 1514 13 12 11 1.10 (.0433) max 0.05 ?0.15 (.002 ?.006) 0.65 (.0256) bsc 2.94 (.116) 0.195 ?0.30 (.0077 ?.0118) typ 2 recommended solder pad layout 0.45 0.05 0.65 bsc 4.50 0.10 6.60 0.10 1.05 0.10 2.94 (.116) 3.58 (.141) 3.58 (.141) millimeters (inches) *dimensions do not include mold flash. mold flash shall not exceed 0.150mm (.006") per side note:1. controlling dimension: millimeters 2. dimensions are in 3. drawing not to scale see note 4 4. recommended minimum pcb metal size for exposed pad attachment 6.40 (.252) bsc downloaded from: http:///
20 lt1764 series 1764fb lt 1205 rev b printed in usa ? linear technology corporation 2005 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com related parts part number description comments lt1120 125ma low dropout regulator with 20 a i q includes 2.5v reference and comparator lt1121 150ma micropower low dropout regulator 30 a i q , sot-223 package lt1129 700ma micropower low dropout regulator 50 a quiescent current lt1175 500ma negative low dropout micropower regulator 45 a i q , 0.26v dropout voltage, sot-223 package lt1374 4.5a, 500khz step-down converter 4.5a, 0.07 ? internal switch, so-8 package lt1521 300ma low dropout micropower regulator with shutdown 15 a i q , reverse battery protection lt1529 3a low dropout regulator with 50 a i q 500mv dropout voltage lt1573 ultrafast tm transient response low dropout regulator drives external pnp lt1575 ultrafast transient response low dropout regulator drives external n-channel mosfet lt1735 synchronous step-down converter high efficiency, opti-loop ? compensation lt1761 series 100ma, low noise, low dropout micropower regulators in sot-23 20 a quiescent current, 20 v rms noise, sot-23 package lt1762 series 150ma, low noise, ldo micropower regulators 25 a quiescent current, 20 v rms noise, msop package lt1763 series 500ma, low noise, ldo micropower regulators 30 a quiescent current, 20 v rms noise, so-8 package lt1962 300ma, low noise, ldo micropower regulator 20 v rms noise, msop package lt1963 1.5a, low noise, fast transient response ldo 40 v rms noise, sot-223 package ultrafast is a trademark of linear technology corporation.opti-loop is a registered trademark of linear technology corporation. typical applicatio u paralleling of regulators for higher output current lt1764-3.3 gnd inshdn out fb lt1764 gnd in r66.65k c222 f 3.3v6a shdn out adj shdn + r74.12k r5 1k c3 0.01 f 3 r4 2.2k r2 0.01 ? r3 2.2k 2 1 8 1764 ta05 4 + c1100 f + 1/2 lt1366 r1 0.01 ? v in > 3.7v downloaded from: http:///

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