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1 lt1121/lt1121-3.3/lt1121-5 micropower low dropout regulators with shutdown n 0.4v dropout voltage n 150ma output current n 30 m a quiescent current n no protection diodes needed n adjustable output from 3.8v to 30v n 3.3v and 5v fixed output voltages n controlled quiescent current in dropout n shutdown n 16 m a quiescent current in shutdown n stable with 0.33 m f output capacitor n reverse battery protection n no reverse current with input low n thermal limiting the lt ? 1121/lt1121-3.3/lt1121-5 are micropower low dropout regulators with shutdown. these devices are capable of supplying 150ma of output current with a dropout voltage of 0.4v. designed for use in battery- powered systems, the low quiescent current, 30 m a oper- ating and 16 m a 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 in- clude the ability to operate with very small output capaci- tors. they are stable with only 0.33 m f on the output while most older devices require between 1 m f and 100 m f for stability. small ceramic capacitors can be used, enhancing manufacturability. also the input may be connected to ground or a reverse voltage without reverse current flow 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 16 m a will flow from the output pin to ground. n low current regulator n regulator for battery-powered systems n post regulator for switching supplies 5v battery-powered supply with shutdown 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 dropout voltage in out lt1121-3.3 gnd 3.3v out 150ma 1 m f solid tantalum 5v 8 + 5 1 3 lt1121 ?ta01 v shdn (pin 5) <0.25 >2.8 nc output off on on shdn features descriptio u applicatio s u typical applicatio u , ltc and lt are registered trademarks of linear technology corporation.
2 lt1121/lt1121-3.3/lt1121-5 output short-circuit duration ......................... indefinite operating junction temperature range (note 3) lt1121c-x ........................................... 0 c to 125 c lt1121i-x ....................................... C 40 c to 125 c storage temperature range ................. C 65 c to 150 c lead temperature (soldering, 10 sec).................. 300 c input voltage lt1121 ............................................................. 30v lt1121hv ............................................. +36v, C 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 wu u package / o rder i for atio t jmax = 150 c, q ja ? 150 c/ w t jmax = 150 c, q ja ? 50 c/ w 1 2 3 bottom view in gnd out z package 3-lead plastic to-92 3 2 1 front view tab is gnd output gnd v in st package 3-lead plastic sot-223 order part number order part number lt1121cz-3.3 lt1121iz-3.3 lt1121cz-5 lt1121iz-5 consult factory for military grade parts. lt1121cn8 lt1121cn8-3.3 lt1121cn8-5 lt1121in8 lt1121in8-3.3 lt1121in8-5 lt1121cs8 lt1121cs8-3.3 lt1121cs8-5 lt1121hvcs8 lt1121is8 1121 11213 11215 1121h 1121i 121i3 121i5 121ih 1121a 121a3 121a5 121ah 121ai 121ai3 121ai5 121aih lt1121cst-3.3 lt1121ist-3.3 lt1121cst-5 lt1121ist-5 s8 part marking order part number 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 = 150 c, q ja ? 120 c/ w (n8, s8) t jmax = 150 c, q ja ? 70 c/ w (as8) absolute axi u rati gs w ww u (note 1) lt1121is8-3.3 lt1121is8-5 lt1121hvis8 lt1121acs8 lt1121acs8-3.3 lt1121acs8-5 LT1121AHVCS8 lt1121ais8 lt1121ais8-3.3 lt1121ais8-5 lt1121ahvis8
3 lt1121/lt1121-3.3/lt1121-5 parameter conditions min typ max units regulated output voltage lt1121-3.3 v in = 3.8v, i out = 1ma, t j = 25 c 3.250 3.300 3.350 v (note 4) 4.3v < v in < 20v, 1ma < i out < 150ma l 3.200 3.300 3.400 v lt1121-5 v in = 5.5v, i out = 1ma, t j = 25 c 4.925 5.000 5.075 v 6v < v in < 20v, 1ma < i out < 150ma l 4.850 5.000 5.150 v lt1121 (note 5) v in = 4.3v, i out = 1ma, t j = 25 c 3.695 3.750 3.805 v 4.8v < v in < 20v, 1ma < i out < 150ma l 3.640 3.750 3.860 v line regulation lt1121-3.3 d v in = 4.8v to 20v, i out = 1ma l 1.5 10 mv lt1121-5 d v in = 5.5v to 20v, i out = 1ma l 1.5 10 mv lt1121 (note 5) d v in = 4.3v to 20v, i out = 1ma l 1.5 10 mv load regulation lt1121-3.3 d i load = 1ma to 150ma, t j = 25 cC12C25mv d i load = 1ma to 150ma l C20 C40 mv lt1121-5 d i load = 1ma to 150ma, t j = 25 cC17C35mv d i load = 1ma to 150ma l C28 C50 mv lt1121 (note 5) d i load = 1ma to 150ma, t j = 25 cC12C25mv d i load = 1ma to 150ma l C18 C40 mv dropout voltage i load = 1ma, t j = 25 c 0.13 0.16 v (note 6) i load = 1ma l 0.25 v i load = 50ma, t j = 25 c 0.30 0.35 v load = 50ma l 0.50 v i load = 100ma, t j = 25 c 0.37 0.45 v i load = 100ma l 0.60 v i load = 150ma, t j = 25 c 0.42 0.55 v i load = 150ma l 0.70 v ground pin current i load = 0ma l 30 50 m a (note 7) i load = 1ma l 90 120 m a i load = 10ma l 350 500 m a i load = 50ma l 1.5 2.5 ma i load = 100ma l 4.0 7.0 ma i load = 150ma l 7.0 14.0 ma adjust pin bias current (notes 5, 8) t j = 25 c 150 300 na shutdown threshold v out = off to on l 1.2 2.8 v v out = on to off l 0.25 0.75 v shutdown pin current (note 9) v shdn = 0v l 610 m a quiescent current in shutdown (note 10) v in = 6v, v shdn = 0v l 15 22 m a ripple rejection v in C v out = 1v (avg), v ripple = 0.5v p-p ,5058db f ripple = 120hz, i load = 0.1a current limit v in C v out = 7v, t j = 25 c 200 500 ma input reverse leakage current v in = C20v, v out = 0v l 1.0 ma reverse output current (note 11) lt1121-3.3 v out = 3.3v, v in = 0v 16 25 m a lt1121-5 v out = 5v, v in = 0v 16 25 m a lt1121 (note 5) v out = 3.8v, v in = 0v 16 25 m a the l denotes specifications which apply over the operating temperature range, otherwise specifications are at t a = 25 c. 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 note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. electrical characteristics
4 lt1121/lt1121-3.3/lt1121-5 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 110 c, a minimum load of 1ma is recommended. for t j > 110 c and i out < 1ma, output voltage may increase by 1%. note 4: operating conditions are limited by maximum junction temperature. the regulated output voltage specification 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 limited. when operating at maximum output current the input voltage range must be limited. note 5: the lt1121 (adjustable version) is tested and specified with the adjust pin connected to the output pin. electrical characteristics note 6: dropout voltage is the minimum input/output voltage required to maintain regulation at the specified 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 flows into the adjust pin. note 9: shutdown pin current at v shdn = 0v flows out of the shutdown pin. note 10: quiescent current in shutdown is equal to the sum total of the shutdown pin current (6 m a) and the ground pin current (9 m a). note 11: reverse output current is tested with the input pin grounded and the output pin forced to the rated output voltage. this current flows into the output pin and out of the ground pin. lt1121-3.3 quiescent current guaranteed dropout voltage dropout voltage quiescent current lt1121 quiescent current lt1121-5 quiescent current 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 g27 20 60 140 160 0 100 = test points t j 125 c t j 25 c temperature ( c) ?0 dropout voltage (v) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 50 75 1121 g14 ?5 25 100 125 i load = 150ma i load = 50ma i load = 1ma i lload = 100ma temperature ( c) ?0 quiescent current ( m a) 10 40 30 20 10 0 0 50 75 1121 g11 ?5 25 100 125 v in = 6v r load = v shdn =0v v shdn = open input voltage (v) 0 quiescent current ( m a) 120 100 80 60 40 20 0 8 1121 g03 2 4 6 10 13579 v shdn = 0v t j = 25 c r load = v out = v adj v shdn = open input voltage (v) 0 quiescent current ( m a) 120 100 80 60 40 20 0 8 1121 g02 2 4 6 10 13579 t j = 25 c r load = v shdn = 0v v shdn = open input voltage (v) 0 quiescent current ( m 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 typical perfor a ce characteristics uw
5 lt1121/lt1121-3.3/lt1121-5 lt1121-3.3 output voltage lt1121-5 output voltage temperature ( c) ?0 output voltage (v) 3.83 3.81 3.79 3.77 3.75 3.73 3.71 3.69 3.67 0 50 75 1121 g24 ?5 25 100 125 i out = 1ma lt1121 adjust pin voltage temperature (?) ?0 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 g22 ?5 25 100 125 i out = 1ma temperature ( c) ?0 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 g23 ?5 25 100 125 i out = 1ma typical perfor a ce characteristics uw lt1121-5 ground pin current lt1121 ground pin current lt1121-3.3 ground pin current input voltage (v) 0 ground pin current ( m a) 800 700 600 500 400 300 200 100 0 8 1121 g10 2 4 6 10 13579 r load = 130 w i load = 25ma* r load = 330 w i load = 10ma* r load = 3.3k i load = 1ma* t j = 25 c *for v out = 3.3v lt1121-3.3 ground pin current input voltage (v) 0 ground pin current ( m a) 800 700 600 500 400 300 200 100 0 8 1121 g06 2 4 6 10 13579 t j = 25 c r load = 500 w i load = 10ma* r load = 5k i load = 1ma* r load = 200 w i load = 25ma* *for v out = 5v lt1121 ground pin current input voltage (v) 0 ground pin current (ma) 10 9 8 7 6 5 4 3 2 1 0 8 1121 g09 2 4 6 10 13579 t j = 25 c r load = 22 w i load = 150ma* r load = 33 w i load = 100ma* r load = 66 w i load = 50ma* *for v out = 3.3v input voltage (v) 0 ground pin current (ma) 10 9 8 7 6 5 4 3 2 1 0 8 1121 g05 2 4 6 10 13579 t j = 25 c r load = 50 w i load = 100ma* r load = 100 w i load = 50ma* r load = 33 w i load = 150ma* *for v out = 5v lt1121-5 ground pin current input voltage (v) 0 ground pin current (ma) 10 9 8 7 6 5 4 3 2 1 0 8 1121 g07 2 4 6 10 13579 t j = 25 c v out = v adj r load = 25 w i load = 150ma* r load = 38 w i load = 100ma* r load = 75 w i load = 50ma* *for v out = 3.75v input voltage (v) 0 ground pin current ( m a) 800 700 600 500 400 300 200 100 0 8 1121 g08 2 4 6 10 13579 t j = 25 c v out = v adj r load = 150 w i load = 25ma* r load = 380 w i load = 10ma* r load = 3.8k i load = 1ma* *for v out = 3.75v
6 lt1121/lt1121-3.3/lt1121-5 ground pin current output current (ma) ground pin current (ma) 14 12 10 8 6 4 2 0 40 80 120 1121 g29 20 60 140 160 0 100 t j = 125 c t j = ?5 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 shutdown pin threshold (on-to-off) shutdown pin threshold (off-to-on) temperature ( c) ?0 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 g16 ?5 25 100 125 i load = 1ma temperature ( c) ?0 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 ?5 25 100 125 i load = 1ma i load = 150ma typical perfor a ce characteristics uw reverse output current shutdown pin current temperature ( c) ?0 output pin current ( m a) 30 25 20 15 10 5 0 0 50 75 1121 g13 ?5 25 100 125 v in = 0v v out = 5v (lt1121-5) v out = 3.3v (lt1121-3.3) v out = 3.8v (lt1121) temperature ( c) ?0 adjust pin bias current (na) 400 350 300 250 200 150 100 50 0 0 50 75 1121 g25 ?5 25 100 125 temperature ( c) ?0 current limit (ma) 400 350 300 250 200 150 100 50 0 0 50 75 1121 g19 ?5 25 100 125 v in = 7v v out = 0v lt1121 adjust pin bias current current limit shutdown pin voltage (v) 0 0 shutdown pin input current (ma) 5 15 20 25 2 4 59 1121 g28 10 13 6 7 8 shutdown pin input current current limit input voltage (v) 0 short-circuit current (ma) 400 350 300 250 200 150 100 50 0 2 4 5 1121 g20 1 3 6 7 v out = 0v temperature ( c) ?0 shutdown pin current ( m a) 10 9 8 7 6 5 4 3 2 1 0 0 50 75 1121 g15 ?5 25 100 125 v shdn = 0v
7 lt1121/lt1121-3.3/lt1121-5 reverse output current output voltage (v) 0 output pin current ( m a) 100 90 80 70 60 50 40 30 20 10 0 8 1121 g01 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 frequency (hz) ripple rejection (db) 100 90 80 70 60 50 40 30 20 10 0 10 1k 10k 1m 1121 g26 100 100k c out = 1 m f solid tantalum c out = 47 m f solid tantalum i out = 100ma v in = 6v + 50mv rms ripple ripple rejection ripple rejection temperature ( c) ?0 ripple rejection (db) 64 62 60 58 56 54 52 50 0 50 75 1121 g18 ?5 25 100 125 v in = v out (nominal) + 1v + 0.5v p-p ripple at f = 120hz i out = 100ma typical perfor a ce characteristics uw load regulation lt1121-5 load transient response lt1121-5 load transient response time (ms) 0 output voltage deviation (v) 0.2 0.1 0 0.1 0.2 0.8 1121 g30 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 m f c out = 1 m f time (ms) 0 output voltage deviation (v) 0.2 0.1 0 0.1 0.2 0.8 1121 g31 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 m f c out = 3.3 m f temperature ( c) ?0 load regulation (mv) 0 ? ?0 ?5 ?0 ?5 ?0 ?5 ?0 0 50 75 1121 g21 ?5 25 100 125 lt1121* lt1121-5 lt1121-3.3 d i load = 1ma to 150ma * adj pin tied to output pin
8 lt1121/lt1121-3.3/lt1121-5 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 filter 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 0.1 m f to 1 m f is sufficient. 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 flow into the lt1121 and no reverse voltage 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 6 m a. 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 microam- peres. 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 character- istics. 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 amplifier. this pin is internally clamped to 6v and C 0.6v (one v be ). it has a bias current of 150na which flows into the pin. see bias current curve in the typical performance characteristics. the adjust pin refer- ence voltage is 3.75v referenced to ground. the output voltage range that can be produced by this device is 3.75v to 30v. uu u pi fu ctio s
9 lt1121/lt1121-3.3/lt1121-5 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 (30 m a). in shutdown the quiescent current drops to only 16 m a. in addition to the low quiescent current the lt1121 incorporates several protection features which make it ideal for use in battery- 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 flow. adjustable operation the adjustable version of the lt1121 has an output voltage range of 3.75v to 20v. 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 25 c, flows 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 coefficient of approximately 15ppm/ c. the adjust pin bias current has a negative temperature coefficient. these effects are small and will tend to cancel each other. the adjustable device is specified with the adjust pin tied to the output pin. this sets the output voltage to 3.75v. specifications 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: 12 375 12 38 v v mv mv . ? ? ? ? () = () thermal considerations power handling capability will be limited by maximum rated junction temperature (125 c). 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 limit- ing designed to protect the device during overload condi- tions. for continuous normal load conditions the maxi- mum junction temperature rating of 125 c 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 + applicatio s i for atio wu uu
10 lt1121/lt1121-3.3/lt1121-5 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 50 c, 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 50 c/w to 65 c/w depending on copper area. so the junction temperature rise above ambient will be less than or equal to: 0.405w ? 60 c/w = 24 c the maximum junction temperature will then be equal to the maximum junction temperature rise above ambient plus the maximum ambient temperature or: t jmax = 50 c + 24 c = 74 c table 5. to-92 package thermal resistance package alone 220 c/w package soldered into pc board with plated 175 c/w through holes only package soldered into pc board with 1/4 sq. inch of 145 c/w copper trace per lead 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 160 c/w aavid type 5754 135 c/w output capacitance and transient performance the ltc1121 is designed to be stable with a wide range of output capacitors. the minimum recommended value is 1 m f with an esr of 3 w or less. for applications where space is very limited, capacitors as low as 0.33 m f can be used if combined with a small series resistor. assuming thermal resistance (junction-to-ambient) thermal resistance (junction-to-ambient) table 1. n8 package* copper area topside backside board area 2500 sq mm 2500 sq. mm 2500 sq. mm 80 c/w 1000 sq mm 2500 sq. mm 2500 sq. mm 80 c/w 225 sq mm 2500 sq. mm 2500 sq. mm 85 c/w 1000 sq mm 1000 sq. mm 1000 sq. mm 91 c/w * device is mounted on topside. leads are through hole and are soldered to both sides of board. table 2. s8 package copper area topside* backside board area 2500 sq. mm 2500 sq. mm 2500 sq. mm 120 c/w 1000 sq. mm 2500 sq. mm 2500 sq. mm 120 c/w 225 sq. mm 2500 sq. mm 2500 sq. mm 25 c/w 100 sq. mm 1000 sq. mm 1000 sq. mm 131 c/w * device is mounted on topside. table 4. sot-223 package (thermal resistance junction-to-tab 20 c/w) copper area topside* backside board area 2500 sq. mm 2500 sq. mm 2500 sq. mm 50 c/w 1000 sq. mm 2500 sq. mm 2500 sq. mm 50 c/w 225 sq. mm 2500 sq. mm 2500 sq. mm 58 c/w 100 sq. mm 2500 sq. mm 2500 sq. mm 64 c/w 1000 sq. mm 1000 sq. mm 1000 sq. mm 57 c/w 1000 sq. mm 0 1000 sq. mm 60 c/w * tab of device attached to topside copper thermal resistance (junction-to-ambient) table 3. as8 package* copper area topside** backside board area 2500 sq. mm 2500 sq. mm 2500 sq. mm 60 c/w 1000 sq. mm 2500 sq. mm 2500 sq. mm 60 c/w 225 sq. mm 2500 sq. mm 2500 sq. mm 68 c/w 100 sq. mm 2500 sq. mm 2500 sq. mm 74 c/w * pins 3, 6, and 7 are ground. ** device is mounted on topside. taken in still air, on 3/32" fr-4 board with 1oz copper. all nc leads were connected to the ground plane. applicatio s i for atio wu uu
11 lt1121/lt1121-3.3/lt1121-5 that the esr of the capacitor is low (ceramic) the sug- gested series resistor is shown in table 5. the lt1121 is a micropower device and output transient response will be a function of output capacitance. see the transient re- sponse curves in the typical performance characteristics. larger values of output capacitance will decrease the peak deviations and provide improved output transient re- sponse. bypass capacitors, used to decouple individual components powered by the lt1121, will increase the effective value of the output capacitor. table 5. suggested series output capacitance resistor 0.33 m f2 w 0.47 m f1 w 0.68 m f1 w >1 m f none needed protection features the lt1121 incorporates several protection features which make it ideal for use in battery-powered circuits. in addi- tion to the normal protection features associated with monolithic regulators, such as current limiting and ther- mal limiting, the device is 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 of 30v. current flow into the device will be limited to less than 1ma (typically less than 100 m a) 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 fixed 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 flow out of 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. 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 flow 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 6 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 flows through the output pin to ground. the state of the shut- down 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 rectified ac source. if the ac source is removed, then the input of the lt1121 is effectively left floating. 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 floating. output voltage (v) 0 output pin current ( m 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 figure 2. reverse output current applicatio s i for atio wu uu
12 lt1121/lt1121-3.3/lt1121-5 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 2 m a (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. input voltage (v) 0 input current ( m 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) figure 3. input current table 6. fault conditions input pin shdn pin output pin 1.5v open (hi) 0v output current = short-circuit current C 30v < v in < 30v grounded 0v output current = 0 applicatio s i for atio wu uu
13 lt1121/lt1121-3.3/lt1121-5 dimensions in inches (millimeters) unless otherwise noted. u package descriptio 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 1098 0.100 (2.54) bsc 0.065 (1.651) typ 0.045 ?0.065 (1.143 ?1.651) 0.130 0.005 (3.302 0.127) 0.020 (0.508) min 0.018 0.003 (0.457 0.076) 0.125 (3.175) min 12 3 4 87 6 5 0.255 0.015* (6.477 0.381) 0.400* (10.160) max 0.009 ?0.015 (0.229 ?0.381) 0.300 ?0.325 (7.620 ?8.255) 0.325 +0.035 0.015 +0.889 0.381 8.255 () *these dimensions do not include mold flash or protrusions. mold flash or protrusions shall not exceed 0.010 inch (0.254mm) 0.016 ?0.050 (0.406 ?1.270) 0.010 ?0.020 (0.254 ?0.508) 45 0 ?8 typ 0.008 ?0.010 (0.203 ?0.254) so8 1298 0.053 ?0.069 (1.346 ?1.752) 0.014 ?0.019 (0.355 ?0.483) typ 0.004 ?0.010 (0.101 ?0.254) 0.050 (1.270) bsc 1 2 3 4 0.150 ?0.157** (3.810 ?3.988) 8 7 6 5 0.189 ?0.197* (4.801 ?5.004) 0.228 ?0.244 (5.791 ?6.197) dimension does not include mold flash. mold flash shall not exceed 0.006" (0.152mm) per side dimension does not include interlead flash. interlead flash shall not exceed 0.010" (0.254mm) per side * **
14 lt1121/lt1121-3.3/lt1121-5 st package 3-lead plastic sot-223 (ltc dwg # 05-08-1630) dimensions in inches (millimeters) unless otherwise noted. u package descriptio 0.114 ?0.124 (2.90 ?3.15) 0.248 ?0.264 (6.30 ?6.71) 0.130 ?0.146 (3.30 ?3.71) 0.264 ?0.287 (6.70 ?7.30) 0.0905 (2.30) nom 0.033 ?0.041 (0.84 ?1.04) 0.181 (4.60) nom 0.024 ?0.033 (0.60 ?0.84) 0.071 (1.80) max 10 max 0.012 (0.31) min 0.0008 ?0.0040 (0.0203 ?0.1016) 10 ?16 0.010 ?0.014 (0.25 ?0.36) 10 ?16 st3 (sot-233) 1298
15 lt1121/lt1121-3.3/lt1121-5 z package 3-lead plastic to-92 (similar to to-226) (ltc dwg # 05-08-1410) dimensions in inches (millimeters) unless otherwise noted. u package descriptio 0.050 (1.27) bsc 0.060 0.005 (1.524 0.127) dia 0.90 (2.286) nom 0.180 0.005 (4.572 0.127) 0.180 0.005 (4.572 0.127) 0.500 (12.70) min 0.050 (1.270) max uncontrolled lead dimension 0.016 0.003 (0.406 0.076) 5 nom 0.015 0.002 (0.381 0.051) 0.060 0.010 (1.524 0.254) 10 nom 0.140 0.010 (3.556 0.127) z3 (to-92) 1098 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.
16 lt1121/lt1121-3.3/lt1121-5 ? linear technology corporation 1994 1121fb lt/lcg 0900 2k rev b ? printed in usa related parts linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 l fax: (408) 434-0507 l www.linear-tech.com part number description comments lt1120 125ma low dropout regulator with 20 m a i q includes 2.5v reference and comparator lt1129 700ma micropower low dropout regulator 50 m a quiescent current lt1175 500ma negative low dropout micropower regulator 45 m a i q , 0.26v dropout voltage, sot-223 package lt1521 300ma low dropout micropower regulator with shutdown 15 m a i q , reverse battery protection lt1529 3a low dropout regulator with 50 m a i q 500mv dropout voltage lt1611 inverting 1.4mhz switching regulator 5v to C 5v at 150ma, low output noise, sot-23 package lt1613 1.4mhz single-cell micropower dc/dc converter sot-23 package, internally compensated ltc1627 high efficiency synchronous step-down switching regulator burst mode tm operation, monolithic, 100% duty cycle lt1682 doubler charge pump with low noise linear regulator low output noise: 60 m v rms (100khz bw) lt1762 series 150ma, low noise, ldo micropower regulator 25 m a quiescent current, 20 m v rms noise lt1763 series 500ma, low noise, ldo micropower regulator 30 m a quiescent current, 20 m v rms noise lt1764 series 3a fast transient response ldo 300mv dropout, 40 m v rms noise lt1962 series 300ma, low noise, ldo micropower regulator 30 m a quiescent current, 20 m v rms noise lt1963 series 1.5a fast transient response ldo 300mv dropout, 40 m v rms noise burst mode is a trademark of linear technology corporation.

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