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lt1121/lt1121-3.3/lt1121-5 1 1121ff typical application features applications description micropower low dropout regulators with shutdown the lt ? 1121/lt1121-3.3/lt1121-5 are micropower low dropout regulators with shutdown. these devices are ca- pable of supplying 150ma of output current with a dropout voltage of 0.4v. designed for use in battery-powered sys- tems, the low quiescent current, 30a operating and 16a in shutdown, makes them an ideal choice. the quiescent current is well-controlled; it does not rise in dropout as it does with many other low dropout pnp regulators. other features of the lt1121/lt1121-3.3/lt1121-5 include the ability to operate with very small output capacitors. they are stable with only 0.33f on the output while most older devices require between 1f and 100f for stability. small ceramic capacitors can be used, enhancing manufactur- ability. also the input may be connected to ground or a reverse voltage without reverse current ? ow from output to input. this makes the lt1121 series ideal for backup power situations where the output is held high and the input is at ground or reversed. under these conditions only 16a will ? ow from the output pin to ground. 5v battery-powered supply with shutdown n 0.4v dropout voltage n 150ma output current n 30a quiescent current n no protection diodes needed n adjustable output from 3.75v to 30v n 3.3v and 5v fixed output voltages n controlled quiescent current in dropout n shutdown n 16a quiescent current in shutdown n stable with 0.33f output capacitor n reverse battery protection n no reverse current with input low n thermal limiting n available in the 8-lead so, 8-lead pdip , 3-lead sot-23 and 3-lead to-92 packages n low current regulator n regulator for battery-powered systems n post regulator for switching supplies l , lt, ltc and ltm are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. dropout voltage in out lt1121-3.3 gnd 3.3v out 150ma 1 f solid tantalum 5v 8 + 5 1 3 lt1121 ? ta01 v shdn (pin 5) <0.25 >2.8 nc output off on on shdn output current (ma) 0 dropout voltage (v) 0.3 0.4 0.5 60 100 160 0.2 0.1 0 20 40 80 120 140 lt1121 ? ta02
lt1121/lt1121-3.3/lt1121-5 2 1121ff absolute maximum ratings input voltage lt1121 .............................................................. 30v lt1121hv ............................................... +36v, ? 30v output pin reverse current ................................. 10ma adjust pin current ................................................ 10ma shutdown pin input voltage (note 2) .......... 6.5v, C 0.6v shutdown pin input current (note 2) .................. 20ma (note 1) 1 2 3 4 8 7 6 5 top view out nc/adj* gnd nc in nc** nc** shdn n8 package 8-lead pdip s8 package 8-lead plastic so pin 2 = nc for lt1121-3.3/lt1121-5 = adj for lt1121 pins 6 and 7 are floating (no internal connection) on the standard s8 package. pins 6 and 7 connected to ground on the a version of the lt1121 (s8 only). connecting pins 6 and 7 to the ground plane will reduce thermal resistance. see thermal resistance tables in the applications information section. * ** t jmax = 150c, ja = 120c/w (n8, s8) t jmax = 150c, ja = 70c/w (as8) 3 2 1 front view tab is gnd output gnd v in st package 3-lead plastic sot-223 t jmax = 150c, ja = 50c/w bottom view in gnd out z package 3-lead plastic to-92 t jmax = 150c, ja = 150c/w order part number s8 part marking order part number st part marking order part number lt1121cn8 lt1121cn8-3.3 lt1121cn8-5 lt1121in8 lt1121in8-3.3 lt1121in8-5 lt1121cs8 lt1121cs8-3.3 lt1121cs8-5 lt1121hvcs8 lt1121is8 lt1121is8-3.3 lt1121is8-5 lt1121hvis8 lt1121acs8 lt1121acs8-3.3 lt1121acs8-5 lt1121ahvcs8 lt1121ais8 lt1121ais8-3.3 lt1121ais8-5 lt1121ahvis8 1121 11213 11215 1121hv 1121i 121i3 121i5 121hvi 1121a 121a3 121a5 121ahv 121ai 121ai3 121ai5 21ahvi lt1121cst-3.3 lt1121ist-3.3 lt1121cst-5 lt1121ist-5 11213 121i3 11215 1121i5 lt1121cz-3.3 lt121iz-3.3 lt1121cz-5 lt1121iz-5 order options tape and reel: add #tr lead free: add #pbf lead free tape and reel: add #trpbf lead free part marking: http://www.linear.com/leadfree/ consult ltc marketing for parts speci? ed with wider operating temperature ranges. package/order information output short-circuit duration ....................... inde? nite operating junction temperature range (note 3) lt1121c-x ............................................ 0c to 125c lt1121i-x ........................................ ? 40c to 125c storage temperature range ...................C 65c to 150c lead temperature (soldering, 10 sec) .................. 300c
lt1121/lt1121-3.3/lt1121-5 3 1121ff electrical characteristics parameter conditions min typ max units regulated output voltage (note 4) lt1121-3.3 v in = 3.8v, i out = 1ma, t j = 25oc 4.3v < v in < 20v, 1ma < i out < 150ma l 3.25 3.2 3.3 3.3 3.35 3.4 v v lt1121-5 v in = 5.5v, i out = 1ma, t j = 25oc 6v < v in < 20v, 1ma < i out < 150ma l 4.925 4.85 5 5 5.075 5.15 v v lt1121 (note 5) v in = 4.3v, i out = 1ma, t j = 25oc 4.8v < v in < 20v, 1ma < i out < 150ma l 3.695 3.64 3.75 3.75 3.805 3.86 v v line regulation lt1121-3.3 v in = 4.8v to 20v, i out = 1ma lt1121-5 v in = 5.5v to 20v, i out = 1ma lt1121 (note 5) v in = 4.3v to 20v, i out = 1ma l l l 1.5 1.5 1.5 10 10 10 mv mv mv load regulation lt1121-3.3 i load = 1ma to 150ma, t j = 25oc i load = 1ma to 150ma lt1121-5 i load = 1ma to 150ma, t j = 25oc i load = 1ma to 150ma lt1121 (note 5) i load = 1ma to 150ma, t j = 25oc i load = 1ma to 150ma l l l C12 C20 C17 C28 C12 C18 C25 C40 C35 C50 C25 C40 mv mv mv mv mv mv dropout voltage (note 6) i load = 1ma, t j = 25oc i load = 1ma l 0.13 0.16 0.25 v v i load = 50ma, t j = 25oc i load = 50ma l 0.3 0.35 0.5 v v i load = 100ma, t j = 25oc i load = 100ma l 0.37 0.45 0.6 v v i load = 150ma, t j = 25oc i load = 150ma l 0.42 0.55 0.7 v v ground pin current (note 7) i load = 0ma i load = 1ma i load = 10ma i load = 50ma i load = 100ma i load = 150ma l l l l l l 30 90 350 1.5 4 7 50 120 500 2.5 7 14 a a a ma ma ma adjust pin bias current (notes 5, 8) t j = 25oc 150 300 na shutdown threshold v out = off to on v out = on to off l l 0.25 1.2 0.75 2.8 v v shutdown pin current (note 9) v shdn = 0v l 610 a quiescent current in shutdown (note 10) v in = 6v, v shdn = 0v l 16 22 a ripple rejection v in C v out = 1v (avg), v ripple = 0.5v p-p , f ripple = 120hz, i load = 0.1a 50 58 db current limit v in C v out = 7v, t j = 25oc 200 500 ma input reverse leakage current v in = C20v, v out = 0v l 1ma reverse output current (note 11) lt1121-3.3 v out = 3.3v, v in = 0v lt1121-5 v out = 5v, v in = 0v lt1121 (note 5) v out = 3.8v, v in = 0v 16 16 16 25 25 25 a a a the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c.
lt1121/lt1121-3.3/lt1121-5 4 1121ff electrical characteristics guaranteed dropout voltage dropout voltage quiescent current the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: the shutdown pin input voltage rating is required for a low impedance source. internal protection devices connected to the shutdown pin will turn on and clamp the pin to approximately 7v or C 0.6v. this range allows the use of 5v logic devices to drive the pin directly. for high impedance sources or logic running on supply voltages greater than 5.5v, the maximum current driven into the shutdown pin must be limited to less than 20ma. note 3: for junction temperatures greater than 110c, a minimum load of 1ma is recommended. for t j > 110c and i out < 1ma, output voltage may increase by 1%. note 4: operating conditions are limited by maximum junction temperature. the regulated output voltage speci? cation will not apply for all possible combinations of input voltage and output current. when operating at maximum input voltage, the output current range must be typical performance characteristics limited. when operating at maximum output current the input voltage range must be limited. note 5: the lt1121 (adjustable version) is tested and speci? ed with the adjust pin connected to the output pin. note 6: dropout voltage is the minimum input/output voltage required to maintain regulation at the speci? ed output current. in dropout the output voltage will be equal to: (v in C v dropout ). note 7: ground pin current is tested with v in = v out (nominal) and a current source load. this means that the device is tested while operating in its dropout region. this is the worst case ground pin current. the ground pin current will decrease slightly at higher input voltages. note 8: adjust pin bias current ? ows into the adjust pin. note 9: shutdown pin current at v shdn = 0v ? ows out of the shutdown pin. note 10: quiescent current in shutdown is equal to the sum total of the shutdown pin current (6a) and the ground pin current (9a). note 11: reverse output current is tested with the input pin grounded and the output pin forced to the rated output voltage. this current ? ows into the output pin and out of the ground pin. output current (ma) dropout voltage (v) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 40 80 120 1121 g01 20 60 140 160 0 100 = test points t j 125 c t j 25 c temperature ( c) C50 dropout voltage (v) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 50 75 1121 g02 C25 25 100 125 i load = 150ma i load = 50ma i load = 1ma i load = 100ma temperature ( c) C50 quiescent current ( a) 50 40 30 20 10 0 0 50 75 1121 g03 C25 25 100 125 v in = 6v r load = v shdn = open v shdn = 0v
lt1121/lt1121-3.3/lt1121-5 5 1121ff typical performance characteristics lt1121-3.3 quiescent current lt1121-5 quiescent current lt1121 quiescent current lt1121-3.3 output voltage lt1121-5 output voltage lt1121 adjust pin voltage lt1121-3.3 ground pin current lt1121-5 ground pin current lt1121 ground pin current input voltage (v) 0 quiescent current ( a) 120 100 80 60 40 20 0 8 1121 g04 2 4 6 10 13579 v shdn = 0v t j = 25 c r load = v shdn = open input voltage (v) 0 quiescent current ( a) 120 100 80 60 40 20 0 8 1121 g05 2 4 6 10 13579 t j = 25 c r load = v shdn = 0v v shdn = open input voltage (v) 0 quiescent current ( a) 120 100 80 60 40 20 0 8 1121 g06 2 4 6 10 13579 v shdn = 0v t j = 25 c r load = v out = v adj v shdn = open temperature ( c) C50 adj pin voltage (v) 3.83 3.81 3.79 3.77 3.75 3.73 3.71 3.69 3.67 0 50 75 1121 g09 C25 25 100 125 i out = 1ma temperature ( c) C50 output voltage (v) 5.08 5.06 5.04 5.02 5.00 4.98 4.96 4.94 4.92 0 50 75 1121 g08 C25 25 100 125 i out = 1ma temperature (c) C50 output voltage (v) 3.38 3.36 3.34 3.32 3.30 3.28 3.26 3.24 3.22 0 50 75 1121 g07 C25 25 100 125 i out = 1ma input voltage (v) 0 ground pin current ( a) 800 700 600 500 400 300 200 100 0 8 1121 g11 2 4 6 10 13579 t j = 25 c r load = 500 i load = 10ma* r load = 5k i load = 1ma* r load = 200 i load = 25ma* *for v out = 5v input voltage (v) 0 ground pin current ( a) 800 700 600 500 400 300 200 100 0 8 1121 g12 2 4 6 10 13579 t j = 25 c v out = v adj r load = 150 i load = 25ma* r load = 380 i load = 10ma* r load = 3.8k i load = 1ma* *for v out = 3.75v input voltage (v) 0 ground pin current ( a) 800 700 600 500 400 300 200 100 0 8 1121 g10 2 4 6 10 13579 r load = 130 i load = 25ma* r load = 330 i load = 10ma* r load = 3.3k i load = 1ma* t j = 25 c *for v out = 3.3v
lt1121/lt1121-3.3/lt1121-5 6 1121ff typical performance characteristics lt1121-3.3 ground pin current lt1121-5 ground pin current lt1121 ground pin current ground pin current shutdown pin threshold (on-to-off) shutdown pin threshold (off-to-on) shutdown pin current shutdown pin input current lt1121 adjust pin bias current input voltage (v) 0 ground pin current (ma) 10 9 8 7 6 5 4 3 2 1 0 8 1121 g14 2 4 6 10 13579 t j = 25 c r load = 50 i load = 100ma* r load = 100 i load = 50ma* r load = 33 i load = 150ma* *for v out = 5v input voltage (v) 0 ground pin current (ma) 10 9 8 7 6 5 4 3 2 1 0 8 1121 g15 2 4 6 10 13579 t j = 25 c v out = v adj r load = 25 i load = 150ma* r load = 38 i load = 100ma* r load = 75 i load = 50ma* *for v out = 3.75v input voltage (v) 0 ground pin current (ma) 10 9 8 7 6 5 4 3 2 1 0 8 1121 g13 2 4 6 10 13579 t j = 25 c r load = 22 i load = 150ma* r load = 33 i load = 100ma* r load = 66 i load = 50ma* *for v out = 3.3v output current (ma) ground pin current (ma) 14 12 10 8 6 4 2 0 40 80 120 1121 g16 20 60 140 160 0 100 t j = 125 c t j = C55 c t j = 25 c v in = 3.3v (lt1121-3.3) v in = 5v (lt1121-5) v in = 3.75v (lt1121) device is operating in dropout temperature ( c) C50 shutdown threshold (v) 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0 50 75 1121 g17 C25 25 100 125 i load = 1ma temperature ( c) C50 shutdown threshold (v) 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0 50 75 1121 g18 C25 25 100 125 i load = 1ma i load = 150ma temperature ( c) C50 shutdown pin current ( a) 10 9 8 7 6 5 4 3 2 1 0 0 50 75 1121 g19 C25 25 100 125 v shdn = 0v shutdown pin voltage (v) 0 0 shutdown pin input current (ma) 5 15 20 25 2 4 59 1121 g20 10 13 6 7 8 temperature ( c) C50 adjust pin bias current (na) 400 350 300 250 200 150 100 50 0 0 50 75 1121 g21 C25 25 100 125
lt1121/lt1121-3.3/lt1121-5 7 1121ff typical performance characteristics reverse output current current limit current limit reverse output current ripple rejection ripple rejection load regulation lt1121-5 load transient response lt1121-5 load transient response temperature ( c) C50 output pin current ( a) 30 25 20 15 10 5 0 0 50 75 1121 g22 C25 25 100 125 v in = 0v v out = 5v (lt1121-5) v out = 3.3v (lt1121-3.3) v out = 3.8v (lt1121) input voltage (v) 0 short-circuit current (ma) 400 350 300 250 200 150 100 50 0 2 4 5 1121 g23 1 3 6 7 v out = 0v temperature ( c) C50 current limit (ma) 400 350 300 250 200 150 100 50 0 0 50 75 1121 g24 C25 25 100 125 v in = 7v v out = 0v output voltage (v) 0 output pin current ( a) 100 90 80 70 60 50 40 30 20 10 0 8 1121 g25 2 4 6 10 13579 t j = 25 c v in = 0v current flows into output pin lt1121-3.3 lt1121 (v out = v adj ) lt1121-5 temperature ( c) C50 ripple rejection (db) 64 62 60 58 56 54 52 50 0 50 75 1121 g26 C25 25 100 125 v in = v out (nominal) + 1v + 0.5v p-p ripple at f = 120hz i out = 100ma frequency (hz) ripple rejection (db) 100 90 80 70 60 50 40 30 20 10 0 10 1k 10k 1m 1121 g27 100 100k c out = 1 f solid tantalum c out = 47 f solid tantalum i out = 100ma v in = 6v + 50mv rms ripple temperature ( c) C50 load regulation (mv) 0 C5 C10 C15 C20 C25 C30 C35 C40 0 50 75 1121 g28 C25 25 100 125 lt1121* lt1121-5 lt1121-3.3 i load = 1ma to 150ma * adj pin tied to output pin time (ms) 0 output voltage deviation (v) 0.2 0.1 0 C0.1 C0.2 0.8 1121 g29 0.1 0.4 0.6 1.0 150 100 load current (ma) 0.2 0.3 0.5 0.7 0.9 v in = 6v c in = 0.1 f c out = 1 f time (ms) 0 output voltage deviation (v) 0.2 0.1 0 C0.1 C0.2 0.8 1121 g30 0.1 0.4 0.6 1.0 150 100 50 load current (ma) 0.2 0.3 0.5 0.7 0.9 v in = 6v c in = 0.1 f c out = 3.3 f
lt1121/lt1121-3.3/lt1121-5 8 1121ff pin functions input pin: power is supplied to the device through the input pin. the input pin should be bypassed to ground if the device is more than six inches away from the main input ? lter capacitor. in general the output impedance of a battery rises with frequency so it is usually adviseable to include a bypass capacitor in battery-powered circuits. a bypass capacitor in the range of 0.1f to 1f is suf? cient. the lt1121 is designed to withstand reverse voltages on the input pin with respect to both ground and the output pin. in the case of a reversed input, which can happen if a battery is plugged in backwards, the lt1121 will act as if there is a diode in series with its input. there will be no reverse current ? ow into the lt1121 and no reverse volt- age will appear at the load. the device will protect both itself and the load. output pin: the output pin supplies power to the load. an output capacitor is required to prevent oscillations. see the applications information section for recommended value of output capacitance and information on reverse output characteristics. shutdown pin: this pin is used to put the device into shutdown. in shutdown the output of the device is turned off. this pin is active low. the device will be shut down if the shutdown pin is pulled low. the shutdown pin current with the pin pulled to ground will be 6a. the shutdown pin is internally clamped to 7v and C 0.6v (one v be ). this allows the shutdown pin to be driven directly by 5v logic or by open collector logic with a pull-up resistor. the pull-up resistor is only required to supply the leakage current of the open collector gate, normally several microamperes. pull-up current must be limited to a maximum of 20ma. a curve of shutdown pin input current as a function of voltage appears in the typical performance characteristics. if the shutdown pin is not used it can be left open circuit. the device will be active, output on, if the shutdown pin is not connected. adjust pin: for the adjustable lt1121, the adjust pin is the input to the error ampli? er. this pin is internally clamped to 6v and C0.6v (one v be ). it has a bias current of 150na which ? ows into the pin. see bias current curve in the typical performance characteristics. the adjust pin reference voltage is 3.75v referenced to ground. the output voltage range that can be produced by this device is 3.75v to 30v.
lt1121/lt1121-3.3/lt1121-5 9 1121ff applications information the lt1121 is a micropower low dropout regulator with shutdown, capable of supplying up to 150ma of output current at a dropout voltage of 0.4v. the device operates with very low quiescent current (30a). in shutdown the quiescent current drops to only 16a. in addition to the low quiescent current the lt1121 incorporates several protection features which make it ideal for use in bat- tery-powered systems. the device is protected against both reverse input voltages and reverse output voltages. in battery backup applications where the output can be held up by a backup battery when the input is pulled to ground, the lt1121 acts like it has a diode in series with its output and prevents reverse current ? ow. adjustable operation the adjustable version of the lt1121 has an output voltage range of 3.75v to 30v. the output voltage is set by the ratio of two external resistors as shown in figure 1. the device servos the output voltage to maintain the voltage at the adjust pin at 3.75v. the current in r1 is then equal to 3.75v/r1. the current in r2 is equal to the sum of the current in r1 and the adjust pin bias current. the adjust pin bias current, 150na at 25c, ? ows through r2 into the adjust pin. the output voltage can be calculated according to the formula in figure 1. the value of r1 should be less than 400k to minimize errors in the output voltage caused by the adjust pin bias current. note that in shutdown the output is turned off and the divider current will be zero. curves of adjust pin voltage vs temperature and adjust pin bias current vs temperature appear in the typical performance characteristics. the reference voltage at the adjust pin has a slight positive temperature coef? cient of approximately 15ppm/c. the adjust pin bias current has a negative temperature coef? cient. these effects are small and will tend to cancel each other. the adjustable device is speci? ed with the adjust pin tied to the output pin. this sets the output voltage to 3.75v. speci? cations for output voltage greater than 3.75v will be proportional to the ratio of the desired output voltage to 3.75v (v out /3.75v). for example: load regulation for an output current change of 1ma to 150ma is C12mv typical at v out = 3.75v. at v out = 12v, load regulation would be: 12v 3.75 v ? ?12mv () = ?38mv () thermal considerations power handling capability will be limited by maximum rated junction temperature (125c). power dissipated by the device will be made up of two components: 1. output current multiplied by the input/output voltage differential: i out ? (v in C v out ), and 2. ground pin current multiplied by the input voltage: i gnd ? v in . the ground pin current can be found by examining the ground pin current curves in the typical performance characteristics. power dissipation will be equal to the sum of the two components listed above. the lt1121 series regulators have internal thermal limiting designed to protect the device during overload conditions. for continuous normal load conditions the maximum junc- tion temperature rating of 125c must not be exceeded. it is important to give careful consideration to all sources of thermal resistance from junction to ambient. additional heat sources mounted nearby must also be considered. heat sinking, for surface mount devices, is accomplished by using the heat spreading capabilities of the pc board and its copper traces. copper board stiffeners and plated through holes can also be used to spread the heat gener- ated by power devices. tables 1 through 5 list thermal resistances for each package. measured values of thermal resistance for several different board sizes and copper areas are listed for each package. all measurements were figure 1. adjustable operation in lt1121 gnd shdn 1121 ? f01 adj out r2 r1 v out = 3.75v 1 + + i adj ? r2 v adj = 3.75v i adj = 150na at 25 c output range = 3.75v to 30v r2 r1 () () v out +
lt1121/lt1121-3.3/lt1121-5 10 1121ff applications information table 1. n8 package* copper area thermal resistance junction to ambient topside backside board area 2500 sq mm 2500 sq mm 2500 sq mm 80oc/w 1000 sq mm 2500 sq mm 2500 sq mm 80oc/w 225 sq mm 2500 sq mm 2500 sq mm 85oc/w 1000 sq mm 1000 sq mm 1000 sq mm 91oc/w * device is mounted on topside. leads are through hole and are soldered to both sides of board. taken in still air, on 3/32" fr-4 board with 1oz copper. all nc leads were connected to the ground plane. table 2. s8 package copper area thermal resistance junction to ambient topside* backside board area 2500 sq mm 2500 sq mm 2500 sq mm 120oc/w 1000 sq mm 2500 sq mm 2500 sq mm 120oc/w 225 sq mm 2500 sq mm 2500 sq mm 125oc/w 100 sq mm 1000 sq mm 1000 sq mm 131oc/w * device is mounted on topside. table 3. as8 package* copper area thermal resistance junction to ambient topside** backside board area 2500 sq mm 2500 sq mm 2500 sq mm 60oc/w 1000 sq mm 2500 sq mm 2500 sq mm 60oc/w 225 sq mm 2500 sq mm 2500 sq mm 68oc/w 100 sq mm 2500 sq mm 2500 sq mm 74oc/w * pins 3, 6 and 7 are ground. ** device is mounted on topside. table 4. sot-223 package (thermal resistance junction-to-tab 20oc/w) copper area thermal resistance junction to ambient topside* backside board area 2500 sq mm 2500 sq mm 2500 sq mm 50oc/w 1000 sq mm 2500 sq mm 2500 sq mm 50oc/w 225 sq mm 2500 sq mm 2500 sq mm 58oc/w 100 sq mm 2500 sq mm 2500 sq mm 64oc/w 1000 sq mm 2500 sq mm 1000 sq mm 57oc/w 1000 sq mm 0 1000 sq mm 60oc/w * tab of device attached to topside copper. table 5. to-92 package thermal resistance package alone 220oc/w package soldered into pc board with plated through holes only 175oc/w package soldered into pc board with 1/4 sq. inch of copper trace per lead 145oc/w package soldered into pc board with plated through holes in board, no extra copper trace, and a clip-on type heat sink: thermalloy type 2224b 160oc/w aavid type 5754 135oc/w calculating junction temperature example: given an output voltage of 3.3v, an input voltage range of 4.5v to 7v, an output current range of 0ma to 100ma, and a maximum ambient temperature of 50c, what will the maximum junction temperature be? power dissipated by the device will be equal to: i out max ? (v in max C v out ) + (i gnd ? v in ) where, i out max = 100ma v in max = 7v i gnd at (i out = 100ma, v in = 7v) = 5ma so, p = 100ma ? (7v C 3.3v) + (5ma ? 7v) = 0.405w if we use an sot-223 package, then the thermal resistance will be in the range of 50c/w to 65c/w depending on copper area. so the junction temperature rise above ambi- ent will be less than or equal to: 0.405w ? 60c/w = 24c the maximum junction temperature will then be equal to the maximum junction temperature rise above ambient plus the maximum ambient temperature or: t jmax = 50c + 24c = 74c output capacitance and transient performance the lt1121 is designed to be stable with a wide range of output capacitors. the minimum recommended value is 1f with an esr of 3 or less. for applications where space is very limited, capacitors as low as 0.33f can be used if combined with a small series resistor. assuming that the esr of the capacitor is low (ceramic) the suggested series
lt1121/lt1121-3.3/lt1121-5 11 1121ff applications information resistor is shown in table 6. the lt1121 is a micropower device and output transient response will be a function of output capacitance. see the transient response curves in the typical performance characteristics. larger values of output capacitance will decrease the peak deviations and provide improved output transient response. bypass capacitors, used to decouple individual components powered by the lt1121, will increase the effective value of the output capacitor. protection features the lt1121 incorporates several protection features which make it 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 device is protected against reverse input voltages, reverse output voltages, and reverse volt- ages 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 operation, the junction temperature should not exceed 125c. the input of the device will withstand reverse voltages of 30v. current ? ow into the device will be limited to less than 1ma (typically less than 100a) and no negative voltage will appear at the output. the device will protect both itself and the load. this provides protection against batteries that can be plugged in backwards. for ? xed voltage versions of the device, the output can be pulled below ground without damaging the device. if the input is open circuit or grounded the output can be pulled below ground by 20v. the output will act like an open circuit, no current will ? ow out of the pin. if the input is powered by a voltage source, the output will source the table 6. suggested series resistor values output capacitance suggested series resistor 0.33f 2 0.47f 1 0.68f 1 >1f none needed short-circuit current of the device and will protect itself by thermal limiting. for the adjustable version of the device, the output pin is internally clamped at one diode drop below ground. reverse current for the adjustable device must be limited to 5ma. 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 ? ow back into the output will vary depending on the conditions. many battery-powered cir- cuits incorporate some form of power management. the following information will help optimize battery life. table 7 summarizes the following information. the reverse output current will follow the curve in figure 2 when the input pin is pulled to ground. this current ? ows through the output pin to ground. the state of the shutdown pin will have no effect on output current when the input pin is pulled to ground. in some applications it may be necessary to leave the input to the lt1121 unconnected when the output is held high. this can happen when the lt1121 is powered from a recti? ed ac source. if the ac source is removed, then the input of the lt1121 is effectively left ? oating. the reverse output current also follows the curve in figure 2 if the input pin is left open. the state of the shutdown pin will have no effect on the reverse output current when the input pin is ? oating. figure 2. reverse output current output voltage (v) 0 output pin current ( a) 100 90 80 70 60 50 40 30 20 10 0 8 1121? f02 2 4 6 10 13579 t j = 25 c v in < v out current flows into output pin to ground lt1121-3.3 lt1121 (v out = v adj ) lt1121-5
lt1121/lt1121-3.3/lt1121-5 12 1121ff applications information table 7. fault conditions input pin shdn pin output pin 1.5v open (hi) 0v output current = short-circuit current C30v < v in < 30v grounded 0v output current = 0 when the input of the lt1121 is forced to a voltage below its nominal output voltage and its output is held high, the reverse output current will still follow the curve in figure 2. this condition can occur if the input of the lt1121 is connected to a discharged (low voltage) battery and the output is held up by either a backup battery or by a second regulator circuit. when the input pin is forced below the output pin or the output pin is pulled above the input pin, the input current will typically drop to less than 2a (see figure 3). the state of the shutdown pin will have no effect on the reverse output current when the output is pulled above the input. figure 3. input current input voltage (v) 0 input current ( a) 5 4 3 2 1 0 4 1121 f03 1 2 3 5 v out = 3.3v (lt1121-3.3) v out = 5v (lt1121-5)
lt1121/lt1121-3.3/lt1121-5 13 1121ff package description n8 package 8-lead pdip (narrow 0.300) (ltc dwg # 05-08-1510) s8 package 8-lead plastic small outline (narrow 0.150) (ltc dwg # 05-08-1610) n8 1002 .065 (1.651) typ .045 ? .065 (1.143 ? 1.651) .130 .005 (3.302 0.127) .020 (0.508) min .018 .003 (0.457 0.076) .120 (3.048) min 12 3 4 87 6 5 .255 .015* (6.477 0.381) .400* (10.160) max .008 ? .015 (0.203 ? 0.381) .300 ? .325 (7.620 ? 8.255) .325 +.035 ?.015 +0.889 ?0.381 8.255 () note: 1. dimensions are inches millimeters *these dimensions do not include mold flash or protrusions. mold flash or protrusions shall not exceed .010 inch (0.254mm) .100 (2.54) bsc .016 ? .050 (0.406 ? 1.270) .010 ? .020 (0.254 ? 0.508) 45 0 ? 8 typ .008 ? .010 (0.203 ? 0.254) so8 0303 .053 ? .069 (1.346 ? 1.752) .014 ? .019 (0.355 ? 0.483) typ .004 ? .010 (0.101 ? 0.254) .050 (1.270) bsc 1 2 3 4 .150 ? .157 (3.810 ? 3.988) note 3 8 7 6 5 .189 ? .197 (4.801 ? 5.004) note 3 .228 ? .244 (5.791 ? 6.197) .245 min .160 .005 recommended solder pad layout .045 .005 .050 bsc .030 .005 typ inches (millimeters) note: 1. dimensions in 2. drawing not to scale 3. these dimensions do not include mold flash or protrusions. mold flash or protrusions shall not exceed .006" (0.15mm)
lt1121/lt1121-3.3/lt1121-5 14 1121ff package description st package 8-lead plastic sot-223 (ltc dwg # 05-08-1630) .114 ? .124 (2.90 ? 3.15) .248 ? .264 (6.30 ? 6.71) .130 ? .146 (3.30 ? 3.71) .264 ? .287 (6.70 ? 7.30) .0905 (2.30) bsc .033 ? .041 (0.84 ? 1.04) .181 (4.60) bsc .024 ? .033 (0.60 ? 0.84) .071 (1.80) max 10 max .012 (0.31) min .0008 ? .0040 (0.0203 ? 0.1016) 10 ? 16 .010 ? .014 (0.25 ? 0.36) 10 ? 16 recommended solder pad layout st3 (sot-233) 0502 .129 max .059 max .059 max .181 max .039 max .248 bsc .090 bsc
lt1121/lt1121-3.3/lt1121-5 15 1121ff 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. package description z package 8-lead plastic to-92 (similar to to-226) (ltc dwg # 05-08-1510) .050 (1.27) bsc .060 .005 (1.524 0.127) dia .90 (2.286) nom .180 .005 (4.572 0.127) .180 .005 (4.572 0.127) .500 (12.70) min .050 (1.270) max uncontrolled lead dimension .016 .003 (0.406 0.076) 5 nom .015 .002 (0.381 0.051) .060 .010 (1.524 0.254) 10 nom .140 .010 (3.556 0.127) z3 (to-92) 0801 321 .098 +.016/?.04 (2.5 +0.4/?0.1) 2 plcs to-92 tape and reel refer to tape and reel section of ltc data book for additional information
lt1121/lt1121-3.3/lt1121-5 16 1121ff linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 1994 lt 0907 rev f ? printed in usa related parts part number description comments lt1120 125ma low dropout regulator with 20a i q includes 2.5v reference and comparator lt1129 700ma micropower low dropout regulator 50a quiescent current lt1175 500ma negative low dropout micropower regulator 45a i q , 0.26v dropout voltage, sot-223 package lt1521 300ma low dropout micropower regulator with shutdown 15a, i q , reverse battery protection lt1529 3a low dropout regulator with 50a i q 500mv dropout voltage lt1611 inverting 1.4mhz switching regulator 5v to C5v at 150ma, low output noise, sot-23 package lt1613 1.4mhz single-cell micropower dc/dc converter sot-23 package, internally compensated lt1627 high ef? ciency synchronous step-down switching regulator burst mode? operation, monolithic, 100% duty cycle lt1682 doubler charge pump with low noise linear regulator low output noise: 60v rms (100khz bw) lt1762 series 150ma, low noise, ldo micropower regulator 25a quiescent current, 20v rms noise lt1763 series 500ma, low noise, ldo micropower regulator 30a quiescent current, 20v rms noise lt1764 series 3a fast transient response ldo 300mv dropout, 40v rms noise lt1962 series 300ma, low noise, ldo micropower regulator 30a quiescent current, 20v rms noise lt1963 series 1.5a fast transient response ldo 300mv dropout, 40v rms noise burst mode is a trademark of linear technology corporation.

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