ltc1798 series 1 1798fb typical application description micropower low dropout references the ltc ? 1798/ltc1798-2.5/ltc1798-3/ltc1798-4.1/ ltc1798-5 are micropower bandgap references that combine high accuracy and low drift with very low supply current and small package size. the combination of ultralow quiescent current and low dropout voltage of only 200mv (max) makes them ideal for battery-powered equipment. the output voltage is set by an external resistor divider for the adjustable ltc1798. this series of references uses curvature compensation to obtain low temperature coef? cient and trimmed thin-? lm resistors to achieve high output accuracy. these references can source up to 10ma and sink up to 2ma, making them ideal for precision regulator applications. they are stable without an output bypass capacitor, but are also stable with capacitance up to 1f. this feature is important in critical applications where pc board space is a premium and fast settling is demanded. the ltc1798 series references provided power dissipation advantages over shunt references. in addition to supply current, shunt references must also idle the entire load current to operate. the ltc1798 series is available in the so-8 package. 2.5v battery-powered reference l , lt, ltc and ltm are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. features applications n 200mv max dropout at 10ma output current n 4a typical quiescent current n 0.15% max initial accuracy n no output capacitor required n output sources 10ma, sinks 2ma n 40ppm/c max drift n voltage options: 2.5v, 3v, 4.1v, 5v and adjustable n battery-powered systems n handheld instruments n precision power supplies n a/d and d/a converters ltc1798-2.5 temperature drift ltc1798-2.5 out in gnd 4 2 2.7v to 12.6v 6 2.5v 1798 ta01 0.1f temperature (c) C40 C20 0 20 40 60 80 100 reference voltage change (mv) 1798 ta02 4 3 2 1 C2 C1 C3 C4 0
ltc1798 series 2 1798fb pin configuration absolute maximum ratings operating temperature range...................... 0c to 70c extended commercial operating temperature range .................................. ?40c to 85c junction temperature ........................................... 110c storage temperature range ................... ?65c to 150c lead temperature (soldering, 10 sec) .................. 300c (note 1) 1 2 3 4 8 7 6 5 top view dnc* dnc* out dnc* *dnc in **dnc/fb gnd s8 package 8-lead plastic so t jmax = 125c, =
ltc1798 series 3 1798fb electrical characteristics note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: the ltc1798 is guaranteed functional over the operating temperature range of C40c to 100c. note 3: if the part is stored outside of the speci? ed operating temperature range, the output may shift due to hysteresis. note 4: esd (electostatic discharge) sensitive device. extensive use of esd protection devices are used internal to the ltc1798, however, high electrostatic discharge can damage or degrade the device. use proper esd handling precautions. note 5: peak-to-peak noise is measured with a single pole highpass ? lter at 0.1hz and 2-pole lowpass ? lter at 10hz. symbol parameter conditions min typ max units v in input voltage range l v i in input current fb = out for ltc1798 l 4 6.5 8.5 a a v out output voltage (note 4) ltc1798, fb = out ltc1798 adj ltc1798-2.5 ltc1798-3 ltc1798-4.1 ltc1798-5 ltc1798 all fixed options 2.3755 C0.4 2.4963 2.9955 4.090 4.9925 C0.15 2.385 2.5 3 4.096 5 2.3945 0.4 2.5037 3.0045 4.102 5.0075 0.15 v % v v v v % e n output voltage noise (note 5) 0.1hz f 10hz 8 ppmp-p tc output voltage temp coef? cient (note 6) t min t j t max l 15 40 ppm/c v out /v in line regulation v in = (v out(nominal) + 0.2v) to 12.6v l 30 120 ppm/v v out /i out load regulation (note 7) sourcing 0ma to 10ma l 0.1 0.3 mv/ma sinking 0ma to 2ma l 1.75 4 6.5 mv/ma mv/ma i sc short-circuit output current v out shorted to gnd v out shorted to v in 20 2 40 4 ma ma v do dropout voltage (note 8) i out = 0, v out 0.1% i out = 10ma, v out 0.1% l l 100 200 mv mv v hyst output hysteresis (note 9) t = C40c to 85c t = 0c to 70c 200 50 ppm ppm i fb fb pin input current ltc1798, out = fb 10 na the l denotes speci? cations which apply over the full speci? ed temperature range, otherwise speci? cations are at t a = 25c. v in = v out(nominal) + 0.2v, i out = 0ma unless otherwise noted. fb = out for the ltc1798. note 6: temperature coef? cient is the change in output voltage divided by the nominal output voltage divided by the speci? ed temperature range. note 7: load regulation is measured on a pulse basis from no load to the speci? ed load current. output changes due to die temperature change must be taken into account separately. note 8: dropout voltage is (v in C v out ) when v out falls to 0.1% below its nominal value at v in = v out + 0.5v. note 9: hysteresis in output voltage is created by package stress that differs depending on whether the ic was previously at a higher or lower temperature. output voltage is always measured at 25c, but the ic is cycled hot or cold before successive measurements. hysteresis is not normally a problem for operational temperature excursions where the instrument might be stored at high or low temperature.
ltc1798 series 4 1798fb typical performance characteristics output source current (ma) dropout voltage (mv) 100 90 80 70 60 50 40 30 20 10 0 0 1 10 100 1798 g01 0.1 t a = 25c temperature (c) C50 C25 input current (a) 150 1798 g02 025 50 75 100 125 8 7 6 5 4 3 2 1 0 v in = 2.7v temperature (c) C50 C25 output short-circuit current (ma) 150 1798 g03 025 50 75 100 125 70 60 50 40 30 20 10 5 0 t a = 25c v in = v out(nom) + 0.2v output shorted to v in output shorted to gnd input voltage (v) 2 output short-circuit current (ma) 25 20 15 10 5 0 4 6810 1798 g04 12 14 t a = 25c output shorted to v in input voltage (v) 2 output short-circuit current (ma) 42 41 4 6810 1798 g05 12 14 t a = 25c output shorted to gnd output current (ma) $ v out from no load (mv) 5 4 3 2 1 0 C1 C2 C3 C4 C5 0 1 10 100 1798 g06 0.1 t a = 25c v in = v out(nom) + 0.2v sinking sourcing input voltage (v) 2 output voltage (v) 2.5010 2.5005 2.5000 2.4995 4 6810 1798 g07 12 14 t a = 25c input voltage (v) 2 input current (a) 7 6 5 4 4 6810 1798 g08 12 14 t a = 25c frequency (hz) power supply rejection ratio (db) 60 50 40 30 20 10 0 10 1k 10k 1798 g09 100 v in = 2.7v ltc1798-2.5* output short-circuit current vs input voltage ltc1798-2.5* output short-circuit current vs input voltage ltc1798 series load regulation ltc1798-2.5* output voltage vs input voltage ltc1798-2.5* input current vs input voltage ltc1798-2.5 psrr vs frequency ltc1798-2.5* dropout voltage vs output source current ltc1798-2.5* input current vs temperature ltc1798 series output short-circuit current vs temperature
ltc1798 series 5 1798fb typical performance characteristics 5v/div 1798 g10 1sec/div v in = 2.7v input voltage (v) 012345678910 input current (a) 1798 g11 1400 1200 1000 800 600 400 200 0 t a = C55c t a = 25c t a = 125c input voltage (v) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 input current (a) 1798 g12 250 200 150 100 50 0 t a = 25c t a = C55c t a = 125c ltc1798-2.5 0.1hz to 10hz noise ltc1798-5 input current vs input voltage in dropout ltc1798-2.5 input current vs input voltage in dropout pin functions dnc (pins 1, 5, 7, 8): do not connect. connected internally for post package trim. these pins must be left unconnected. in (pin 2): positive supply. bypassing with a 0.1f capaci- tor is recommended if the output loading changes. (v out + 0.2v) v in 12.6v. dnc (pin 3): (ltc1798-2.5/ltc1798-3/ltc1798-4.1/ ltc1798-5) do not connect. connected internally for post package trim. this pin must be left unconnected. fb (pin 3): (ltc1798) resistor divider feedback pin. connect a resistor divider from out to gnd and the center tap to fb. this pin sets the output potential. vv rr r out = + 2 385 12 2 .; r1 is connected from out to fb and r2 from fb to gnd. selecting r2 10k will make i out < 250a. gnd (pin 4): negative supply or ground connection. out (pin 6): reference output. the output can source up to 10ma and sink up to 2ma. it is stable with output bypass capacitor ranging from 0f to 1f.
ltc1798 series 6 1798fb figure 1. reference output load transient response, 1f output capacitor 10ms/div v out 100mv/div i out 1ma 0ma 1798 f01a longer battery life series references have an advantage over shunt style references. to operate, shunt references require a resistor between the power supply and the output. this resistor must be chosen to supply the maximum current that is demanded by the circuit being regulated. when the circuit being controlled is not operating at this maximum current, the shunt reference must always sink this current, resulting in high power dissipation and short battery life. the ltc1798 series low dropout references do not require a current setting resistor and can operate with any supply voltage from (v out(nominal ) + 0.2v) to 12.6v. when the circuitry being regulated does not demand current, the ltc1798 series reduces its dissipation and battery life is extended. if the reference is not delivering load current it block diagram C + in 6 1798 bd 2 4 out 3 (ltc1798) fb 2.385v gnd r1 r2 note: r1 and r2 are not connected for ltc1798 0.5ms/div v out 100mv/div i out 1ma 0ma 1798 f01b applications information dissipates only 10.8w when operating on a 2.7v supply for ltc1798-2.5, yet the same connection can deliver 10ma of load current when demanded. output bypass capacitor the ltc1798 series is designed to be stable with or without capacitive loads. with no capacitive load, the reference is ideal for fast settling applications, or where pc board space is at a premium. in applications with signi? cant output loading changes, an output bypass capacitor of up to 1f can be used to improve the output transient response. figure 1 shows the response of the reference to a 1ma to 0a load step with a 1f output capacitor. if more than 1f of output capacitance is required, a resistor in series with the capacitor is recommended
ltc1798 series 7 1798fb ltc1798-5 out in gnd 4 2 5.2v to 12.6v 6 5v 1798 f02 0.1f c out >1f damping resistor <1k applications information figure 2. adding a damping resistor with output capacitors greater than 1f figure 3. damping resistance vs output capacitor value output capacitor value (f) 1 10 resistor value () 100 1k 10k 10 100 1000 1798 f03 these references consume only 4a of quiescent current under light and heavy loads as well as in dropout; whereas, pnp-based references waste considerable amounts of cur- rent when the pass transistor is saturated. in addition, the ltc1798 series provides a lower dropout voltage (200mv max) than pnp-based references. to reduce the output ringing. figure 2 illustrates the use of a damping resistor for capacitive loads greater than 1f. figure 3 shows the resistor and capacitor values required to achieve critical damping. internal p-channel pass transistor the ltc1798 series features an internal p-channel mosfet pass transistor. this provides several advantages over similar designs using a pnp bipolar pass transistor. package description dimensions in inches (millimeters) unless otherwise noted. s8 package 8-lead plastic so (narrow 0.150) (reference ltc dwg # 05-08-1610) 0.016 C 0.050 (0.406 C 1.270) 0.010 C 0.020 (0.254 C 0.508) 45 0C 8 typ 0.008 C 0.010 (0.203 C 0.254) so8 1298 0.053 C 0.069 (1.346 C 1.752) 0.014 C 0.019 (0.355 C 0.483) typ 0.004 C 0.010 (0.101 C 0.254) 0.050 (1.270) bsc 1 2 3 4 0.150 C 0.157** (3.810 C 3.988) 8 7 6 5 0.189 C 0.197* (4.801 C 5.004) 0.228 C 0.244 (5.791 C 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 * **
ltc1798 series 8 1798fb linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com linear technology corporation 2008 lt 0309 rev b ? printed in usa related parts typical application part number description comments lt ? 1389 nanopower precision shunt voltage reference 800na quiescent current, 0.05% max, 10ppm/c max drift 1.25v and 2.5v versions, so-8 package lt1634 micropower precision shunt voltage reference 0.05% max, 25ppm/c max drift, 1.25v, 2.5v, 4.096v and 5v outputs lt1460 micropower series reference 0.075% max, 10ppm/c max drift, 2.5v, 5v and 10v outputs lt1461 micropower precision series voltage reference 0.04% max, 3ppm/c max drift, 35a quiescent current lt1790 sot-23, ldo precision micropower reference 0.05% max, 10ppm/c max, 2.5v, 60a supply + C 1 4 8 v ss = C4v v out = C3v 0.2v v cc 8.5v 3 2 ltc1798-3 1/2 ltc1542 out gnd 4 6 1798 ta03 in 2 0.1f micropower low dropout negative reference ltc1798-2.5 out in gnd 4 2 v cc = 5v 6 2.5v virtual ground 1798 ta04 0.1f 0.1f supply splitter ltc1798-3 ltc1096l mpu serial data link (microwire tm and spi compatible) out in gnd cs/ shdn +in Cin gnd v cc clk d out v ref analog input 0v to 3v range 1 2 3 4 8 7 6 5 4 2 v in 3.2v to 12.6v 6 1798 ta05 1f serial data link 0.1f low power, low voltage supply reference for ltc1096l microwire is a trademark of national semiconductor corporation.
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