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1 for more information www.linear.com/lt6657 typical a pplica t ion fea t ures descrip t ion 1.5ppm/c drift, low noise, buffered reference the lt ? 6657 is a precision voltage reference that combines robust operating characteristics with extremely low drift and low noise. with advanced curvature compensation, this bandgap reference achieves 1.5ppm/c drift with predictable temperature behavior, and an initial voltage accuracy of 0 .1%. it also offers 0.5ppm p-p noise and very low temperature cycling hysteresis. the lt6657 is a low dropout reference that can be powered from as little as 50mv above the output voltage, up to 40v. the buffered output supports 10ma of output drive with low output impedance and precise load regulation . the high sink current capability allows operation as a negative voltage reference with the same precision as a positive reference. this part is safe under reverse battery condi - tions, and includes current protection when the output is short-circuited and thermal shutdown for overload condi - tions. a shutdown is included to allow power reduction while enabling a quick turn-on . the lt6657 is fully specified over the temperature range of C 40 c to 125 c. it is available in the 8-lead msop package. l, lt , lt c , lt m , linear technology and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. basic connection output voltage temperature drift n low drift n a grade: 1.5ppm/c max n b grade: 3ppm/c max n low noise: n 0.5ppm p-p (0.1hz to 10hz) n 0.8ppm rms (10hz to 1khz) n wide supply range to 40v n sources and sinks 10ma min n line regulation: 0.2ppm/v n load regulation: 0.7ppm/ma n reverse supply protection n reverse output protection n low power shutdown: <4a max n thermal protection n can operate in shunt mode n configurable as a negative reference n available output voltage options: 2.5v, 3v, 5v n msop-8 package a pplica t ions n high temperature industrial n high resolution data acquisition systems n instrumentation and process control n automotive control and monitoring n medical equipment n shunt and negative voltage references lt6657 c in 0.1f (v out + 50mv) < v in < 40v out in gnd c out 1f v out 6657 ta01a 2 shdn 3 6 4 temperature (c) ?45 output voltage change (normalized) (ppm) 200 100 ?100 0 ?200 5 105 55 6657 ta01b 130 ?20 80 30 three typical parts 1ppm/c box lt6657 6657fb
2 for more information www.linear.com/lt6657 a bsolu t e maxi m u m r a t ings input voltage v in ( to gnd ) .......................... C 40v to 40v shutdown voltage shdn ............................ C 20v to 40v output voltage v out ..................................... C 3v to 30v i nput-to-output differential voltage ( note 2 ) .......... 40v out put short-circuit duration .......................... inde finite operating junction temperature range ................................................ C 40 c to 1 50c storage temperature range .................. C 65 c to 1 50c lead temperature (soldering 10 sec) ( note 3 ) ............................................................ 300 c (note 1) o r d er i n f or m a t ion tube tape and reel part marking* package description specified temperature range lt6657ahms8-2.5#pbf lt6657ahms8-2.5#trpbf ltgkn 8-lead plastic msop C40c to 125c lt6657bhms8-2.5#pbf lt6657bhms8-2.5#trpbf ltgkn 8-lead plastic msop C40c to 125c lt6657ahms8-3#pbf lt6657ahms8-3#trpbf ltgyg 8-lead plastic msop C40c to 125c lt6657bhms8-3#pbf lt6657bhms8-3#trpbf ltgyg 8-lead plastic msop C40c to 125c lt6657ahms8-5#pbf lt6657ahms8-5#trpbf ltgyh 8-lead plastic msop C40c to 125c lt6657bhms8-5#pbf lt6657bhms8-5#trpbf ltgyh 8-lead plastic msop C40c to 125c * temperature grades are identified by a label on the shipping container . consult ltc marketing for parts specified with wider operating temperature ranges. parts ending with pbf are rohs and weee compliant. for more information on lead free part marking , go to: http://www.linear.com/leadfree/ for more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. some packages are available in 500 unit reels through designated sales channels with #trmpbf suffix. ? this product is only offered in trays. for more information go to: http://www.linear.com/packaging/ a vailable o p t ions output voltage initial accuracy temperature coefficient order part number** specified temperature range 2.5v 0.1% 0.1% 1.5ppm/c 3ppm/c lt6657ahms8-2.5 lt6657bhms8-2.5 C40c to 125c C40c to 125c 3v 0.1% 0.1% 1.5ppm/c 3ppm/c lt6657ahms8-3 lt6657bhms8-3 C40c to 125c C40c to 125c 5v 0.1% 0.1% 1.5ppm/c 3ppm/c lt6657ahms8-5 lt6657bhms8-5 C40c to 125c C40c to 125c ** see the order information section for complete part number listing. 1 2 3 4 dnc v in shdn gnd 8 7 6 5 dnc dnc v out dnc top view ms8 package 8-lead plastic msop t jmax = 150c, ja = 273c/w dnc: connected internally do not connect external circuitry to these pins p in c on f igura t ion http://www .linear.com/product/lt6657#orderinfo lt6657 6657fb
3 for more information www.linear.com/lt6657 e lec t rical c harac t eris t ics parameter conditions min typ max units output voltage accuracy C0.1 0 0.1 % output voltage temperature coefficient (note 4) lt6657a lt6657b l l 0.5 1 1.5 3 ppm/c ppm/c line regulation (note 5) v out + 0.5v v in 40v l 0.2 2 4 ppm/v ppm/v load regulation (note 5) i out (source) = 10ma l 0.7 2 4 ppm/ma ppm/ma i out (sink) = 10ma l 0.9 3 6 ppm/ma ppm/ma shunt configuration v out is shorted to v in i shunt 2.5 to 11ma l 0.9 6 ppm/ma minimum v in C v out v in C v out , v out = 0.1% i out = 0ma l 20 50 70 mv mv i out (source) = 1ma l 65 100 140 mv mv i out (source) = 10ma l 330 450 500 mv mv i out (sink) = 10ma l C230 C150 C50 mv mv shutdown pin (shdn ) logic high input voltage logic high input current, shdn = 1.6v l l 1.6 0.7 2 v a logic low input voltage logic low input current, shdn = 0.8v l l 0.2 0.8 1 v a supply current in shutdown shdn = 0.4v shdn = 0.8v l l 0.01 2.0 4 20 a a supply current no load l 1.2 1.8 2.3 ma ma output short-circuit current short v out to gnd short v out to v in 15 16 ma ma output voltage noise (note 6) 0.1hz f 10hz 10hz f 1khz 0.5 0.8 ppm p-p ppm rms turn-on time 0.1% settling, c l = 1f 180 sec long-term drift of output voltage (note 7) 30 ppm/khr hysteresis (note 8) t = 0c to 50c t = 0c to 70c t = C40c to 85c t = C40c to 125c t = C55c to 125c 20 24 30 35 40 ppm ppm ppm ppm ppm the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. the test conditions are v in ?=?v out ?+?0.5v, v shdn ?=?1.6v, i out ?=?0, c out ?=?1f, unless otherwise noted. 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: with v in at 40v, v out may not be pulled below 0v. the total v in to v out differential voltage must not exceed 40v. note 3: the stated temperature is typical for soldering of the leads during manual rework. for detailed ir reflow recommendations, refer to the application information section. note 4: temperature coefficient is measured by dividing the maximum change in output voltage by the specified temperature range. lt6657 6657fb
4 for more information www.linear.com/lt6657 e lec t rical c harac t eris t ics note 5: line and load regulation are measured on a pulse basis for specified input voltage or load current ranges. output voltage change due to die temperature change must be taken into account separately. note 6: peak-to-peak noise is measured with a 2-pole highpass filter at 0.1hz and 3-pole lowpass filter at 10hz. the unit is enclosed in a still-air environment to eliminate thermocouple effects on the leads, and the test time is 10 seconds. due to the statistical nature of noise, repeating noise measurements will yield larger and smaller peak values in a given measurement interval. by repeating the measurement for 1000 intervals, each 10 seconds long, it is shown that there are time intervals during which the noise is higher than in a typical single interval, as predicted by statistical theory. in general, typical values are considered to be those for which at least 50% of the units may be expected to perform similarly or better. for the 1000 interval test, a typical unit will exhibit noise that is less than the typical value listed in the electrical characteristics table in more than 50% of its measurement intervals. see application note 124 for noise testing details. rms noise is measured with a spectrum analyzer in a shielded environment. note 7: long term stability typically has a logarithmic characteristic and therefore change after 1000 hours tend to be much smaller than before that time. total drift in the second thousand hours is normally less than one third of the first thousand hours with a continuing trend toward reduced drift with time. long-term stability will also be affected by differential stresses between the ic and the board material created during board assembly. note 8 : hysteresis in output voltage is created by mechanical stress that depends on whether the ic was previously at a different temperature. output voltage is always measured at 25c, but the ic is cycled 25c to cold to 25c, or 25c to hot to 25c before successive measurements. hysteresis measures the maximum output change for the averages of three hot or cold temperature cycles, preconditioned by one cold and one hot cycles. for instruments that are stored at well controlled temperatures (within 30 degrees of the operational temperature), hysteresis is usually not a significant error source. lt6657 6657fb
5 for more information www.linear.com/lt6657 2.5v output voltage temperature drift 2.5v low frequency 0.1hz to 10hz noise 2.5v output voltage noise spectrum 2.5v integrated noise 10hz to 10khz 2.5v supply current vs input voltage 2.5v line regulation 2.5v load regulation (sourcing) 2.5v load regulation (sinking) 2.5v minimum v in to v out differential (sourcing) temperature (c) ?50 output voltage (v) 2.5008 2.5004 2.4996 2.5000 2.4992 0 100 50 6657 g01 150 125 ?25 75 25 three typical parts time (1s/div) output noise (500nv/div) 6657 g02 100 10 1 0.1 0.01 1 10 0.1 frequency (khz) integrated noise (v rms ) 6657 g04 c out = 1f input voltage (v) ?40 input current (ma) 2.0 1.5 0.0 0.5 1.0 ?0.5 0 6657 g05 40 20 ?20 ?10 30 10 ?30 v shdn = v in input voltage (v) 0 output voltage (v) 2.5010 2.5005 2.4995 2.5000 2.4990 20 6657 g06 40 30 10 part self heating is included output current (ma) 0.1 output voltage change (ppm) 30 10 ?10 ?20 ?30 20 0 1 6657 g07 10 ms8 package part self heating is included the test conditions are t a = 25c, v in ?=?v out ?+?0.5v, v shdn ?=?1.6v, i out ?=?0, c out ?=?1f, unless otherwise noted. output current (ma) 0.1 output voltage change (ppm) 30 10 ?10 ?20 ?30 20 0 1 6657 g08 10 ms8 package part self heating is included input-output voltage (mv) 0 output current (ma) 10 0.1 1 100 200 300 400 6657 g09 500 typical p er f or m ance c harac t eris t ics lt6657 6657fb 100 50 60 70 80 90 100 110 noise voltage (nv/ hz ) 6657 g03 c out = 1f cer 125c 25c ?40c ?55c 125c 25c ?40c 125c 25c ?40c ?55c 125c c out = 5f cer 25c ?40c ?55c 125c 25c ?40c ?55c c out = 47f tant frequency (khz) 0.01 0.1 1 10
6 for more information www.linear.com/lt6657 typical p er f or m ance c harac t eris t ics the test conditions are t a = 25 c, v in ?=?v out ?+? 0. 5v, v shdn ?=? 1. 6v, i out ?=? 0, c out ?=? 1f, unless otherwise noted . 2.5v supply current in shutdown vs input voltage input voltage (v) 0 supply current in shutdown (a) 4.0 3.0 2.0 1.0 0.0 20 30 6657 g16 40 v shdn = 0.4v shutdown pin current vs shutdown voltage shutdown voltage (v) ?10 shutdown current (a) 10 5 0 ?5 ?10 ?30 ?20 ?15 ?25 20 30 0 10 6657 g15 40 supply and ground currents vs load current shutdown voltage thresholds vs temperature load current (ma) ?10 supply and ground currents (ma) 12 8 4 0 ?4 ?12 ?8 5 ?5 0 6657 g13 10 currents going into the part are positive ground pin current supply pin current temperature (c) ?50 shutdown voltage thresholds (v) 1.40 1.35 1.30 1.25 1.15 1.00 1.10 1.05 100 0 50 6657 g14 150 v th(rising) v th(falling) 5v output voltage temperature drift 5v low frequency 0.1hz to 10hz noise 2.5v minimum v in to v out differential (sinking) 2.5v power supply rejection ratio vs frequency 2.5v output impedance vs frequency input-output voltage (mv) ?300 output current (ma) 10 0.1 1 ?200 ?100 ?250 ?150 ?50 0 6657 g10 50 v in < v out frequency (khz) 0.1 1 power supply rejection ratio (db) 120 80 40 20 0 100 60 100 10 6657 g11 1000 c out = 1f c out = 10f lt6657 6657fb three typical parts temperature (c) ?50 ?30 ?10 10 30 50 70 125c 90 110 130 150 4.9984 4.9992 5.0000 5.0008 5.0016 output voltage (v) 25c ?40c ?55c 6657 g17 time (1s/div) output noise (500nv/div) 6657 g18 125c 25c ?40c ?55c c out = 1f c out = 10f c out = 100f frequency (khz) 1 10 100 1k 0.1 1 10 output impedance () 6657 g12 125c 25c ?40c ?55c 125c 25c ?40c ?55c
7 for more information www.linear.com/lt6657 typical p er f or m ance c harac t eris t ics the test conditions are t a = 25 c, v in ?=?v out ?+? 0. 5v, v shdn ?=? 1. 6v, i out ?=? 0, c out ?=? 1f, unless otherwise noted . 5v output voltage noise spectrum 5v integrated noise 10hz to 10khz 5v supply current vs input voltage 5v line regulation 5v load regulation (sourcing) 5v load regulation (sinking) 5v minimum v in to v out differential (sourcing) 5v minimum v in to v out differential (sinking) 5v output impedance vs frequency lt6657 6657fb 100 1 10 ?30 ?20 ?10 0 10 20 30 output voltage change (ppm) 50 6657 g24 125c 25c ?40c ?55c input?output voltage (mv) 0 100 200 300 100 400 500 0.1 1 10 output current (ma) 6657 g25 v in < v out 125c 25c 150 ?40c ?55c input?output voltage (mv) ?350 ?300 ?250 ?200 ?150 ?100 ?50 200 0 50 0.1 1 10 output current (ma) 6657 g26 c out = 1f c out = 10f c out = 100f 250 frequency (khz) 1 10 100 1k 0.1 1 10 100 output impedance () 300 6657 g27 350 noise voltage (nv/ hz ) 6657 g19 c out = 1f cer c out = 1f frequency (khz) 0.01 0.1 1 10 0.1 1 10 100 c out = 5f cer integrated noise (v rms ) 6657 g20 v shdn = v in 125c 25c ?40c ?55c input voltage (v) ?40 ?30 c out = 47f tant ?20 ?10 0 10 20 30 40 ?0.5 0 0.5 frequency (khz) 1.0 1.5 2.0 input current (ma) 6657 g21 part self heating is included 125c 25c ?40c 0.01 input voltage (v) 0 10 20 30 40 4.9990 4.9995 5.0000 5.0005 0.1 5.0010 output voltage (v) 6657 g22 ms8 package part self heating is included 125c 25c ?40c ?55c output current (ma) 1 0.1 1 10 ?30 ?20 ?10 0 10 20 30 10 output voltage change (ppm) 6657 g23 ms8 package part self heating is included 125c 25c ?40c ?55c output current (ma) 0.1
8 for more information www.linear.com/lt6657 p in func t ions shdn (pin 3): shutdown input. this active low input disables the part to reduce supply current < 2a. this pin must be driven externally and should be tied to v in if unused. it may be driven to logic high or to v in during normal operation. v in ( pin 2): input voltage supply. bypass v in with a local 0.1f or larger capacitor to gnd. gnd ( pin 4): device ground. this pin must be connected to a noise-free ground plane. a star-ground with related circuits will give the best results . be careful of trace im - pedance, as the gnd pin carries supply return current. v out ( pin 6): reference output voltage. this pin can source and sink current to a load . an output capacitor of 1f or higher is required for stability. dnc ( pins 1, 5, 7, 8): internal functions. do not connect or electrically stress these pins. these pins must be left floating and leakage currents from these pins should be kept to a minimum. allow additional routing clearance. b lock diagra m ? + v out 6 v in 2 3 6657 bd bandgap bias error amp shdn gnd 4 rg rf lt6657 6657fb
9 for more information www.linear.com/lt6657 line and load regulation the line regulation of the lt6657 is typically well below 1ppm/v. a 10v change in input voltage causes a typical output shift of only 2ppm. load regulation is also less than 1ppm/ma in an ms8 package. a 5ma change in load cur - rent shifts output voltage by only 4ppm. these electrical effects are measured with low duty cycle pulses . to realize such excellent load regulation the ir drops on the v out and gnd lines need to be minimized. one ounce copper foil printed circuit board has 0.5m/square. just 1m of added trace resistance introduces an error of 1v for each 1ma passing through it. this will add a 0.4ppm/ ma to the load regulation with a 2.5v reference. these externally created errors have the same order of magni - tude as the typical load regulation values for the lt6657. minimizing wire resistance and using a separate ground return for the load will maintain excellent load regulation. when sourcing current , the ground connection pin can be used as kelvin sensing for improved output regulation. additional output changes due to die temperature change must be taken into account separately. these added effects may be estimated from: line_reg (in ppm) = (i in? +?i out ) ? ja ???tc???v in load_reg (in ppm) = (v in ?C?v out )??? ja ???tc???i out where voltages are in v, currents are in ma, package thermal resistance ja is in c/mw, and temperature coefficient, tc, is in ppm/c. for example, with typical quiescent current i in ?= ? 1. 2ma, i out = 1ma, v in C v out ?= ? 1v, the added line-regulation is typically 0. 66ppm/ v and added load-regulation is typically 0.3ppm/ma for a tc of 1ppm/ c and msop-8 package with ja ?=?0.3c/mw thermal resistance. bypass and load capacitors the lt6657 voltage reference requires a 0.1f or larger input capacitor placed close to the part to improve power supply rejection. a long input wire with large series induc - tance can create ringing response to large load transients. the output requires a capacitor of 1f or higher placed near the part. frequency stability, turn-on time and settling a pplica t ions i n f or m a t ion behavior are directly affected by the value and type of the output capacitor . equivalent resistance in series with the output capacitor (esr) introduces a zero in the output buffer transfer function and can cause instability . it is recommended to keep the esr less than 0.5 to maintain sufficient phase margin . both capacitance and esr are frequency dependent. at higher frequencies, capacitance drops and esr increases . to ensure stability above 100khz , the output capacitor must also have suitable character - istics above 100khz. the following paragraphs describe capacitors with suitable performance. for applications requiring a large output capacitor, a low esr ceramic capacitor in parallel with a bulk tantalum capacitor provides an optimally damped response. for example, a 47f tantalum capacitor with larger esr in parallel with a 10f ceramic capacitor with esr smaller than 0.5 improves transient response and increases phase margin. give extra consideration to the use of ceramic capacitors such as x7r types. these capacitors are small, come in appropriate values and are relatively stable over a wide temperature range. however, for low noise requirements, x7r capacitors may not be suitable as they may exhibit a piezoelectric effect. mechanical vibrations cause a charge displacement in the ceramic dielectric and the resulting perturbations can appear as noise. for very low noise applications , film capacitors should be considered for their lack of piezoelectric effects . film capaci - tors such as polyester , pol y carbonate and polypropylene have good temperature stability . additional care must be taken as polypropylene have an upper limit of 85 c to 105 c. above these temperatures the working voltage often needs to be derated per manufacturer specifications . another type of film capacitor is polyphenylene sulfide ( pps ). these capacitors work over a wide temperature range , are stable and have large capacitance values beyond 1f. in voltage reference applications, film capacitor lifetime is affected by temperature and applied voltage. capacitor lifetime is degraded by operating near or exceeding the rated voltage, at high temperature, with ac ripple or some combination of these. most voltage reference applications present ac ripple only during transient events. lt6657 6657fb
10 for more information www.linear.com/lt6657 turn-on and line transient response the turn-on time is slew-limited and determined by the short-circuit current , the output capacitor, and the output voltage value as determined by the equation: t on = v out ? c out i sc for example, the lt6657-2.5v, with a 1f output capaci - tor and a typical current limit of 15ma the turn-on time would be: t on = 2.5v ? 1f 15ma = 167s the resulting turn-on time is shown in figure 1. 50s/div v in 1v/div gnd v out 1v/div gnd 6657 f01 c out = 1f figure 1. 2.5v turn-on characteristics line transient response with a 1f output capacitor and no output current is shown in figure 2. the peak voltage output response is less than 1mv. 50s/div v in 0.2v/div 3v/dc v out 2mv/div 2.5v/dc 6657 f02 c out = 1f, i out = 0ma figure 2. line transient response with v in = 0.4v p-p increasing the output load speeds up the response ( figure ?3 ). 50s/div v in 0.2v/div 3v/dc v out 2mv/div 2.5v/dc 6657 f03 c out = 1f, i out = 1ma sourcing figure 3. line transient response with v in = 0.4v p-p a larger output capacitor lowers the amplitude response with a longer time response trade-off (figure 4). v in 0.5v/div 3v/dc v out 2mv/div 2.5v/dc 6657 f04 c out = 10f, i out = 0ma 50s/div figure 4. line transient response with v in = 1v p-p load transient response the test circuit of figure 5 is used to measure load transient response with various currents. c in 0.1f v in = 3v c out 1f v out v gen 6657 f05 2 3 6 4 1k lt6657 out in gnd shdn figure 5. transient load test circuit a pplica t ions i n f or m a t ion lt6657 6657fb
11 for more information www.linear.com/lt6657 figure 6 and 7 shows the load transient response to a 5ma current step both sourcing and sinking. 50s/div i out 0ma 5ma v out 10mv/div /ac 2.5v/dc 6657 f06 c out = 1f figure 6. output response with a 5ma load step sourcing 50s/div i out 5ma 0ma v out 10mv/div /ac 2.5v dc 6657 f07 c out = 1f figure 7. output response with a 5ma load step sinking figure 8 and 9 shows the load transient response to a smaller 4ma to 5ma current step while sourcing and sinking. 50s/div i out 4ma 5ma v out 2mv/div /ac 2.5v/dc 6657 f08 c out = 1f figure 8. output response with a 4 ma to 5 ma load step sourcing 50s/div i out 5ma 4ma v out 2mv/div /ac 2.5v dc 6657 f09 c out = 1f figure 9. output response with a 4ma to 5ma load step sinking figures 10 and 11 show the load transient response to an even smaller 0. 5ma current step both sourcing and sinking. 50s/div i out 0ma 0.5ma v out 2mv/div/ac 2.5v/dc 6657 f10 c out = 1f figure 10. output response with a 0.5ma load step sourcing 50s/div i out 0.5ma 0ma v out 2mv/div/ac 2.5v/dc 6657 f11 c out = 1f figure 11. output response with a 0.5ma load step sinking a pplica t ions i n f or m a t ion lt6657 6657fb
12 for more information www.linear.com/lt6657 lt6657 sinking current dropout description the lt6657 output stage can source and sink current of equal magnitude. when sourcing current it performs as a conventional low dropout regulating device. when sinking current, it can maintain a regulated output with an input voltage equal to , more positive than, or also slightly less than the output voltage. the specification for dropout voltage while sinking is expressed in negative voltage values for v in C v out . a typical unit will maintain a regulated output voltage while sinking current with an input voltage 250mv (50mv guaranteed ) below the output voltage. lower input voltage will cause the output to drop out of regulation. this allows shunt reference applications where the output and input can be tied together and sink current from the output to ground. positive or negative shunt mode operation in addition to the series mode operation, the lt6657 can be operated in shunt mode. in this mode the reference is wired as a two terminal circuit which can be used both as a positive or a negative voltage reference, as shown in figures 12 and 13. r shunt is chosen using the following formula: r shunt = v dd C v out i shunt _ max where: i shunt_max = 2.5ma + i out_max lt6657 v dd out in gnd c out 1f i out +v out 6657 f12 2 shdn 3 6 4 r shunt figure 12. positive shunt mode operation lt6657 out in gnd c out 1f i out +v out 2 shdn 3 6 4 i out ?v out 6657 f13 ?v dd i shunt r shunt figure 13. negative shunt mode operation the i shunt current has to be operated above 2.5ma to obtain the same performance as the series mode opera - tion. in shunt mode operation i out_max is less than or equal to 8.5ma. a c out of 1f or more is required on the output for stability. shutdown mode when the shdn pin is pulled below 0. 8v with respect to ground, the lt6657 enters a low power state and turns the output off. quiescent current is typically 2a. if shdn is set less than 0. 4v the quiescent current drops to 0. 01 a typical. the shdn pin turn-on threshold is 1. 26v and it has approximately 150mv hysteresis for the turn-off threshold . the turn-on logic high voltage is 1. 6v. drive the shdn with either logic or an open-collector/ drain with a pull-up resistor. the resistor supplies the pull-up current to the open-collector/ drain logic, normally several microamperes, plus the shdn pin current, typically less than 5a at 6v. if unused, connect the shdn input pin to v in . power dissipation power dissipation for lt6657 depends on v in , load current and the package type. the msop-8 package has a thermal resistance of ja = 273c/w. although the maximum junction temperature is 150 c ,for best performance it is recommended to limit the change in junction temperature as much as possible. the plot in a pplica t ions i n f or m a t ion lt6657 6657fb
13 for more information www.linear.com/lt6657 figure 14 shows the maximum ambient temperature limits for different v in and load condition using a maximum junction temperature of 125c in the msop-8 package. if the load current exceeds 10ma the parts could begin to current limit. in this case, the output voltage is no longer regulated and the part could dissipate much more power and operate hotter than the graph shows. v in (v) 0 maximum ambient operating temperature (c) 125 105 65 85 45 115 75 95 55 10 35 2520 6657 f14 40 5 30 15 v out = 2.5v 10ma sink ms8 10ma source ms8 figure 14. maximum ambient operating temperature with a large input voltage and sourcing current , an internal thermal shutdown protection circuit limits the maximum power dissipation. when sinking current, there is no need for thermal shutdown protection because the power dis - sipation is much smaller and the sinking current limit will give some load protection. noise performance and specification the lt6657 offers exceptional low noise for a bandgap reference; only 0.5ppm p-p in the 0.1hz to 10hz bandwidth. as a result system noise performance may be dominated by system design and physical layout. care is required to achieve the best possible noise performance . the use of dissimilar metals in component leads and pc board traces creates thermocouples. variations in thermal resistance, caused by uneven air flow over the circuit board create dif - ferential lead temperature, thereby creating a thermoelectric voltage noise at the output of the reference. minimizing the number of thermocouples , as well as limiting airflow, can substantially reduce these errors . additional information can be found in linear technology application note 82. position the input and load capacitors close to the part. although the lt6657 has 130db dc psrr, the power sup - ply should be as stable as possible to guarantee optimal performance. a plot of the 0.1hz to 10hz low frequency noise is shown in the typical performance characteristics section. noise performance can be further improved by wiring several lt6657 s in parallel as shown in the typical applications section. with this technique the noise is reduced by n, where n is the number of lt6657s used. noise in any frequency band is a random function based on physical properties such as thermal noise, shot noise, and flicker noise. the most precise way to specify a random error such as noise is in terms of its statistics , for example as an rms value . this allows for relatively simple maximum error estimation, generally involving assumptions about noise bandwidth and crest factor. unlike wideband noise, low frequency noise, typically specified in a 0.1hz to 10hz band, has traditionally been specified in terms of expected error, illustrated as peak-to-peak error. low frequency noise is generally measured with an oscilloscope over a 10 second time frame. this is a pragmatic approach, given that it can be difficult to measure noise accurately at low frequencies, and that it can also be difficult to agree on the statistical characteristics of the noise, since flicker noise dominates the spectral density. while practical, a random sampling of 10 second intervals is an inadequate method for representation of low frequency noise, especially for systems where this noise is a dominant limit of system performance . given the random nature of noise, the output voltage may be observed over many time intervals , each giving different results. noise specifications that were determined using this method are prone to subjectivity, and will tend toward a mean statistical value, rather than the maximum noise that is likely to be produced by the device in question. because the majority of voltage reference data sheets express low frequency noise as a typical number, and as it tends to be illustrated with a repeatable plot near the mean of a distribution of peak-to-peak values, the lt6657 data sheet provides a similarly defined typical specification in order to allow a reasonable direct comparison against similar products. data produced with this method generally a pplica t ions i n f or m a t ion lt6657 6657fb
14 for more information www.linear.com/lt6657 a pplica t ions i n f or m a t ion + ? 100k 100k shield shielded can 1n4697 10v ac line ground 1300f v in 100k* 10* + ? 1k* 200* 2k 450* 900* 15v 15v ?15v ?15v 1f 1f a1 lt1012 a2 lt1097 6657 f16 ? input q1 5 a = 10 4 low noise pre-amp reference under test 0.15f 750* 10k ?15v q3 2n2907 q2 0.022f 1f **1.2k shdn lt6657 2.5v in out + 1f 0.1f 124k* 124k* ? + a3 lt1012 1m* 10k* 100* 330* in out 330f 16v 330f 16v + + 330f 16v 330f 16v + ? a4 lt1012 0.1f 0.1f 10k a = 100 and 0.1hz to 10hz filter t + + t = tantalum,wet slug i leak < 5na see text/appendix b to adc/dvm system adc/dvm system figure 15. lt6657 noise test circuitry (from an124) suggests that in a series of 10 second output voltage measurements, at least half the observations should have a peak-to-peak value that is below this number. for example, the lt6657-2.5 measures less than 0.5ppm p-p in at least 50% of the 10 second observations. as mentioned above, the statistical distribution of noise is such that if observed for long periods of time , the peak error in output voltage due to noise may be much larger than that observed in a smaller interval . the likely maxi - mum error due to noise is often estimated using the rms value, multiplied by an estimated crest factor, assumed to be in the range of 6 to 8.4. this maximum possible value will only be observed if the output voltage is measured for very long periods of time . therefore, in addition to the common method, a more thorough approach to measuring noise has been used for the lt6657 (described in detail in linear technology s an124) that allows more information to be obtained from the result. in particular, this method characterizes the noise over a significantly greater length of time, resulting in a more complete description of low frequency noise. the reference noise is measured at the output of the circuit shown in figure 15 with an adc /dvm system. peak-to-peak voltage is then calculated for 10 lt6657 6657fb
15 for more information www.linear.com/lt6657 second intervals over hundreds of intervals . the results are then summarized in terms of the fraction of measurement intervals for which observed noise is below a specified level. for example, the lt6657-2.5 measures less than 0.55ppm p-p in 80 % of the measurement intervals, and less than 0.59ppm p-p in 95% of observation intervals. the preamplifier and filter are shown in figure 15. this statistical variation in noise is illustrated in figure 16. peak-to-peak noise (v p-p ) 0.8 number of observations 6000 4000 2000 0 5000 1000 3000 cumulative probability 1.2 0.8 0.4 0 1 0.2 0.6 1.6 1.21 6657 f16 1.8 1.4 average v p-p = 1.24v figure 16. lt6657 low frequency noise histogram this method of testing low frequency noise is more practical than common methods. the results yield a comprehensive statistical description, rather than a single observation. in addition, the direct measurement of output voltage over time gives an actual representation of peak noise, rather than an estimate based on statistical assumptions such as crest factor. hysteresis thermal hysteresis is a measure of change of output voltage as a result of temperature cycling. figure 17 illustrates the typical hysteresis based on data taken from the lt6657-2.5. a proprietary design technique minimizes thermal hysteresis. the lt6657 is capable of dissipating relatively high power. for example, with a 40v input voltage and 5ma source load current applied to the lt6657-2.5, the power dissipation is pd = 40v ??? 1.4ma + 37.5v ? 5ma = 244mw, which causes an increase in the die temperature of 73c in msop-8 package. this could increase the junction temperature above 125c and may cause the output to shift due to thermal hysteresis each time the device is powered up. change in output voltage (ppm) ?150 number of units 20 12 4 0 16 8 50 ?50 6657 f17 150 0 ?100 100 cold: 25c to ?40c to 25c hot: 25c to 125c to 25c ms8 figure 17. ?v out due to thermal hysteresis a pplica t ions i n f or m a t ion lt6657 6657fb
16 for more information www.linear.com/lt6657 long-term drift the lt6657 drift data was taken on parts that were sol - dered into pc boards similar to a real world application. the boards were then placed into a constant temperature oven with t a = 35c, their outputs scanned regularly and measured with an 8.5 digit dvm. typical long-term drift is illustrated in figure 18a and 18b. time (hours) 0 long term drift (ppm) 80 ?40 ?80 40 0 600 400 6657 f18a 1000 200 800 figure 18a. long-term drift ms8 figure 18b. long-term drift ms8 burn-in 150c/24h figure 18. pc board layout stress the lt6657 is a very stable reference over temperature with less than 1.5ppm/c error as shown in the electrical characteristics table . the mechanical stress caused by soldering parts to a printed circuit board may cause the output voltage to shift and the die temperature coefficient to change. the pc board can affect all aspects of stabil - ity, including long term stability, thermal hysteresis and humidity stability. see linear s an82 for more detailed information. ir reflow shift the mechanical stress of soldering a part to a board can cause the output voltage to shift. moreover, the heat of an ir reflow or convection soldering oven can also cause the output voltage to shift. the materials that make up a semiconductor device and its package have different rates of expansion and contraction. after a part undergoes the extreme heat of a lead-free ir reflow profile, like the one shown in figure 19, the output voltage shifts. after the device expands, due to the heat, and then contracts, the stresses on the die move. this shift is similar to, but larger than thermal hysteresis. minutes 0 temperature (c) 150 225 8 6657 f19 75 0 2 4 6 10 300 t = 150c t s = 190c t l = 217c t p = 260c 380s t p 30s t l 130s 40s 120s ramp down t s(max) = 200c ramp to 150c figure 19. lead-free reflow profile a pplica t ions i n f or m a t ion lt6657 6657fb ?80 ?40 0 40 80 long term drift (ppm) 6657 f18b time (hours) 0 500 1000 1500 2000 2500 3000
17 for more information www.linear.com/lt6657 experimental results of ir reflow shift are shown in figure 20 for ms8. these results show only shift due to reflow and not mechanical stress. change in output voltage (ppm) ?300 number of units 9 3 1 0 5 7 8 6 4 2 100 ?100 6657 f20 300 0 ?200 200 1 cycle 3 cycles ms8 figure 20. ?v out due to ir reflow (ms8 package), peak temperature?=?260c a pplica t ions i n f or m a t ion lt6657 6657fb
18 for more information www.linear.com/lt6657 typical a pplica t ions extended supply range reference boosted output current with current limit boosted output current reference negative shunt mode reference sinking current from external circuitry bzx84c12 270k 40v to 100v 2n3440 6657 ta02 1f 0.1f lt6657 out in gnd shdn 1 2 led1* * led cannot be ommitted the led clamps the voltage drop across the 220 and limits output current 6657 ta04 220 4.7f 1f i out up to 100ma 0.1f 10 2n2905 v out + 2v < v in < 40v lt6657 out in gnd shdn 2n2905 220 4.7f 6657 ta03 1f i out up to 300ma v out + 1.5v < v in < 40v 0.1f lt6657 out in gnd shdn lt6657 out in gnd 1f i out shdn i out ?v out ?v dd i shunt r shunt 6657 ta05 (v out ? 230mv) to 40v 1f v out v ext (>v out ) 6657 ta06 0.1f r load lt6657 out in gnd shdn r shunt = v dd C v out i shunt _max i shunt _max = 2.5ma + i out _max i out _max < 8.5ma lt6657 6657fb
19 for more information www.linear.com/lt6657 low noise statistical averaging reference e nout = e n /n where n is the number of lt6657s in parallel low frequency noise (0.1hz to 10hz) with four lt6657s in parallel 6657 ta07a lt6657 20 gnd in shdn out 1f 0.1f lt6657 20 gnd in shdn out 1f 0.1f lt6657 20 gnd in shdn out 1f 0.1f lt6657 20 gnd in shdn out 1f 0.1f v out = 2.5v 1f 3v to 40v typical a pplica t ions peak-to-peak noise (v p-p ) 0.4 number of observations 9000 5000 2000 0 7000 8000 4000 6000 1000 3000 cumulative probability 1.2 0.8 0.4 0 1 0.2 0.6 0.8 0.9 0.60.5 6657 ta07b 1.0 0.7 average v p-p = 0.63v lt6657 6657fb
20 for more information www.linear.com/lt6657 p ackage descrip t ion please refer to http://www .linear.com/product/lt6657#packaging for the most recent package drawings. msop (ms8) 0213 rev g 0.53 0.152 (.021 .006) seating plane note: 1. dimensions in millimeter/(inch) 2. drawing not to scale 3. dimension does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.152mm (.006") per side 4. dimension does not include interlead flash or protrusions. interlead flash or protrusions shall not exceed 0.152mm (.006") per side 5. lead coplanarity (bottom of leads after forming) shall be 0.102mm (.004") max 0.18 (.007) 0.254 (.010) 1.10 (.043) max 0.22 ? 0.38 (.009 ? .015) typ 0.1016 0.0508 (.004 .002) 0.86 (.034) ref 0.65 (.0256) bsc 0 ? 6 typ detail ?a? detail ?a? gauge plane 1 2 3 4 4.90 0.152 (.193 .006) 8 7 6 5 3.00 0.102 (.118 .004) (note 3) 3.00 0.102 (.118 .004) (note 4) 0.52 (.0205) ref 5.10 (.201) min 3.20 ? 3.45 (.126 ? .136) 0.889 0.127 (.035 .005) recommended solder pad layout 0.42 0.038 (.0165 .0015) typ 0.65 (.0256) bsc ms8 package 8-lead plastic msop (reference ltc dwg # 05-08-1660 rev g) lt6657 6657fb
21 for more information www.linear.com/lt6657 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 . r evision h is t ory rev date description page number a 03/16 conditions added for electrical characteristic, minimum v in C v out 3 b 06/16 added 3v, 5v options changed c l , c load to c out corrected graphs g03, g12 1, 2, 6, 7 9, 10, 11 5, 6 lt6657 6657fb
22 for more information www.linear.com/lt6657 ? linear technology corporation 2015 lt 0616 rev b ? printed in usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com/lt6657 r ela t e d p ar t s typical a pplica t ion part number description comments lt1236 precision low drift, low noise reference 0.05% max, 5ppm/c max, 1ppm (peak-to-peak) noise lt1460 micropower series references 0.075% max, 10ppm/c max, 20ma output current lt1461 micropower series low dropout 0.04% max, 3ppm/c max, 50ma output current lt1790 micropower precision series references 0.05% max, 10ppm/c max, 60a supply, sot23 package lt6660 tiny micropower series reference 0.2% max, 20ppm/c max, 20ma output current, 2mm 2mm dfn LT6650 micropower reference with buffer amplifier 0.5% max, 5.6a supply, sot23 package ltc6652 high precision, buffered voltage reference family 0.05% max initial error, 5ppm/c max drift, shutdown current <2a, C40c to 125c operation lt6654 low noise, high voltage, high output drive voltage reference family 1.6ppm peak-to-peak noise (0.1hz to 10hz), sink/source 10ma, 10ppm/c max drift, C40c to 125c operation ltc6655 precision, very low noise and temperature drift, voltage reference family 0.25ppm peak-to-peak noise (0.1hz to 10hz), sink/source 5ma, 0.025% max, 2ppm/c max drift, C40c to 125c operation lt6656 ultra low current series voltage reference family supply current < 1a, 0.05% max, 10ppm/c, sink/source 5ma low noise precision 20-bit analog-to-digital converter application snr = 97db sinad = 97db thd = ?117db sfdr = 120db 9 sck 47f 10v x7r 1f cnv ref gnd gnd gnd gnd ref/dgc v dd ov dd sck sdo busy rdl/sdi sdo busy rd ltc2378-20 in ? in + 5 4 3 2 1 5 4 13 14 11 12 lt6657 0.1f gnd shdn in v in = 5v 2 3 6 4 out +3.3v 1k 10 16 6 3 1 15 7 2 8 0.1f 0.1f 10f 6.3v +2.5v 0.1f 6800pf ?3.6v npo 3300pf 1206 npo 10 6800pf npo 10f 6.3v 10 v + 8v v ? + ? lt6203 5 6 7 ? + lt6203 v in + v in ? 6657 ta08 lt6657 6657fb

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