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ltc1250 1 1250fb , ltc and lt are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. protected by u.s. patents including 4933642. + 5v ?v 1000pf 18.2k 1000pf 18.2k 7 6 4 3 2 ?v 0.1 f 5v a v = 100 1250 ta01 350 ? strain gauge 50 ? gain trim ltc1250 time (s) 0 v 1 2 8 lt1250 ta02 0 ? ? 2 4 6 10 v s = 5v a v = 10k typical applicatio u applicatio s u descriptio u features very low noise zero-drift bridge amplifier electronic scales strain gauge amplifiers thermocouple amplifiers high resolution data acquisition low noise transducers instrumentation amplifiers very low noise: 0.75 v p-p typ, 0.1hz to 10hz dc to 1hz noise lower than op-07 full output swing into 1k load offset voltage: 10 v max offset voltage drift: 50nv/ c max common mode rejection ratio: 110db min power supply rejection ratio: 115db min no external components required pin compatible with standard 8-pin op amps available in standard 8-pin plastic dip and 8-pin so packages the ltc 1250 is a high performance, very low noise zero- drift operational amplifier. the ltc1250? combination of low front-end noise and dc precision makes it ideal for use with low impedance bridge transducers. the ltc1250 features typical input noise of 0.75 v p-p from 0.1hz to 10hz, and 0.2 v p-p from 0.1hz to 1hz. the ltc1250 has dc to 1hz noise of 0.35 v p-p , surpassing that of low noise bipolar parts including the op-07, op-77, and lt1012. the ltc1250 uses the industry-standard single op amp pinout, and requires no external components or nulling signals, allowing it to be a plug-in replacement for bipolar op amps. the ltc1250 incorporates an improved output stage capable of driving 4.3v into a 1k load with a single 5v supply; it will swing 4.9v into 5k with 5v supplies. the input common mode range includes ground with single power supply voltages above 12v. supply current is 3ma with a 5v supply, and overload recovery times from positive and negative saturation are 0.5ms and 1.5ms, respectively. the internal nulling clock is set at 5khz for optimum low frequency noise and offset drift; no external connections are necessary. the ltc1250 is available in a standard 8-pin plastic dip and 8-pin so packages. input referred noise 0.1hz to 10hz differential bridge amplifier
ltc1250 2 1250fb absolute axi u rati gs w ww u (note 1) total supply voltage (v + to v ) ............................. 18v input voltage ........................ (v + + 0.3v) to (v ?0.3v) output short circuit duration ......................... indefinite storage temperature range ................ 65 c to 150 c lead temperature (soldering, 10 sec.)................ 300 c wu u package / o rder i for atio ltc1250m ltc1250c symbol parameter conditions min typ max min typ max units v os input offset voltage t a = 25 c (note 2) 5 10 5 10 v ? v os average input offset drift (note 2) 0.01 0.05 0.01 0.05 v/ c long term offset drift 50 50 nv/ mo e n input noise voltage (note 3) t a = 25 c, 0.1hz to 10hz 0.75 1.0 0.75 1.0 v p-p t a = 25 c, 0.1hz to 1hz 0.2 0.2 v p-p i n input noise current f = 10hz 4.0 4.0 fa/ hz i b input bias current t a = 25 c (note 4) 50 150 50 200 pa 950 450 pa i os input offset current t a = 25 c (note 4) 100 300 100 400 pa 500 500 pa cmrr common mode rejection ratio v cm = 4v to 3v 110 130 110 130 db psrr power supply rejection ratio v s = 2.375v to 8v 115 130 115 130 db a vol large-signal voltage gain r l = 10k, v out = 4v 125 170 125 170 db maximum output voltage swing r l = 1k 4.0 4.3/?.7 4.0 4.3 /?.7 v r l = 100k 4.92 4.95 v sr slew rate r l = 10k, c l = 50pf 10 10 v/ s gbw gain-bandwidth product 1.5 1.5 mhz i s supply current no load, t a = 25 c 3.0 4.0 3.0 4.0 ma 7.0 5.0 ma operating temperature range ltc1250m (obsolete) ............ ?5 c to 125 c ltc1250c .......................................... 0 c to 70 c 1 2 3 4 8 7 6 5 top view nc ?n +in v nc v + out nc n8 package 8-lead plastic dip order part number ltc1250cn8 t jmax = 110 c, ja = 130 cw obsolete package j8 package 8-lead ceramic dip t jmax = 150 c, ja = 100 cw (j8) ltc1250mj8 ltc1250cj8 order part number ltc1250cs8 t jmax = 110 c, ja = 200 cw s8 part marking 1250 consider the n8 or s8 for alternative source consult ltc marketing for parts specified with wider operating temperature ranges. electrical characteristics the denotes the specifications which apply over the full operating temperature range, v in = 5v, otherwise specifications are at t a = 25 c. 1 2 3 4 8 7 6 5 top view s8 package 8-lead plastic so nc ?n +in v nc v + out nc
ltc1250 3 1250fb ltc1250m ltc1250c symbol parameter conditions min typ max min typ max units f s internal sampling frequency t a = 25 c 4.75 4.75 khz v os input offset voltage t a = 25 c (note 2) 2 5 2 5 v ? v os average input offset drift (note 2) 0.01 0.05 0.01 0.05 v/ c e n input noise voltage (note 3) t a = 25 c, 0.1hz to 10hz 1.0 1.0 v p-p t a = 25 c, 0.1hz to 1hz 0.3 0.3 v p-p i b input bias current t a = 25 c (note 4) 20 100 20 100 pa i os input offset current t a = 25 c (note 4) 40 200 40 200 pa maximum output voltage swing r l = 1k 4.0 4.3 4.0 4.3 v r l = 100k 4.95 4.95 v i s supply current t a = 25 c 1.8 2.5 1.8 2.5 ma f s sampling frequency t a = 25 c 3 3 khz cc hara terist ics uw a t y p i ca lper f o r c e total supply voltage, v + to v (v) 4 2 sampling frequency (khz) 3 4 68 10 12 1250 g03 5 6 14 16 t a = 25 c total supply voltage, v + to v (v) 4 0 supply current (ma) 0.5 1.0 1.5 2.0 68 10 12 1250 g02 2.5 3.0 3.5 4.0 14 16 t a = 25 c total supply voltage, v + to v (v) 4 0 input noise ( v p-p ) 0.2 0.4 0.6 0.8 68 10 12 1250 g01 1.0 1.2 1.4 1.6 14 16 t a = 25 c 0.1hz to 10hz 0.1hz to 1hz sampling frequency vs supply voltage supply current vs supply voltage input noise vs supply voltage note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: these parameters are guaranteed by design. thermocouple effects preclude measurement of these voltage levels during automated testing. note 3: 0.1hz to 10hz noise is specified dc coupled in a 10s window; 0.1hz to 1hz noise is specified in a 100s window with an rc high-pass filter at 0.1hz. the ltc1250 is sample tested for noise; for 100% tested parts contact ltc marketing dept. note 4: at t 0 c these parameters are guaranteed by design and not tested. electrical characteristics the denotes the specifications which apply over the full operating temperature range, v in = 5v, otherwise specifications are at t a
ltc1250 4 1250fb frequency (hz) 20 cmrr (db) 40 80 120 140 1 100 1k 100k 1250 g12 0 10 10k 60 100 v s = 5v v cm = 1v rms supply voltage ( v) 2 ? input common mode range (v) ? ? ? 0 34 5 6 1250 g11 2 4 6 8 7 8 t a = 25 c temperature ( c) ?5 10 100 1000 100 75 1250 g09 ?0 125 bias current ( | pa | ) 50 025 v s = 5v frequency (hz) 0 gain (db) 20 40 60 100 1k 100k 1m 10m 1250 g08 ?0 10k 80 0 phase margin (deg) 20 40 60 100 ?0 80 gain phase: r l = 1k phase: r l = 100k v s = 5v or single 5v t a = 25 c c l = 100pf frequency (hz) 20 voltage noise (nv/ hz) 30 40 50 80 1 100 1k 10k 1250 g07 0 10 70 60 10 v s = 5v r s = 10 ? temperature ( c) ?0 sampling frequency (khz) 4 5 6 25 1250 g06 3 2 ?5 0 50 1 0 8 7 75 100 150 v s = 5v temperature ( c) ?0 2.0 supply current (ma) 3.0 4.5 0 50 75 1250 g05 2.5 4.0 3.5 ?5 25 100 125 v s = 5v temperature ( c) ?0 input noise ( v p-p ) 0.8 1.0 1.2 25 75 1250 g04 0.6 0.4 ?5 0 50 100 125 0.2 0 v s = 5v 0.1hz to 10hz 0.1hz to 1hz cc hara terist ics uw a t y p i ca lper f o r c e sampling frequency vs temperature supply current vs temperature input noise vs temperature common mode rejection ratio vs frequency 0.2 0 0 ? input (v) 500 s/div a v = 100, r l = 100k, c l = 50pf, v s = 5v output (v) overload recovery common mode input range vs supply voltage voltage noise vs frequency gain/phase vs frequency bias current (magnitude) vs temperature
ltc1250 5 1250fb 100pf 100k output 1250 tc02 + 5v 7 6 4 3 2 ?v ltc1250 10 ? + 7 5 6 0.02 f 800k + 3 2 800k 800k 0.04 f 0.01 f 1/2 lt1057 5v 8 1 4 ?v 1/2 lt1057 + 5v 100pf 100k 7 6 4 3 2 ?v output 1250 tc01 ltc1250 10 ? temperature ( c) ?0 0 10 20 25 1250 g18 ?0 ?0 ?5 0 50 ?0 ?0 40 75 100 125 short-circuit current (ma) 30 v s = 15v v out = v v out = v + output current (ma) 0.01 2 output voltage (v) 3 4 5 0.1 1 10 1250 g17 1 0 6 v s = single 5v output current (ma) 0.01 ? output voltage (v) 0 1 2 3 0.1 1 10 1250 g16 ? ? ? ? 4 5 v s = 5v load resistance (k ? ) 0 0 output swing (v) 4 6 8 18 12 2 4 59 1250 g15 2 14 16 10 13 6 7 8 v s = 16v v s = 10v v s = 5v 10 v = gnd r l to gnd load resistance (k ? ) 0 output swing ( v) 6 8 10 8 1250 g14 4 2 0 2 4 6 10 1 3 5 7 9 1357 9 r l to gnd v s = 8v v s = 5v v s = 2.5v negative swing positive swing 1 s/div a v = 1, r l = 100k, c l = 50pf, v s = 5v transient response output swing vs load resistance, dual supplies output voltage swing vs load resistance, single supply cc hara terist ics uw a t y p i ca lper f o r c e test circuits offset test circuit dc to 10hz noise test circuit (for dc to 1hz multiply all capacitor values by 10) 2v/div output swing vs output current, 5v supply short-circuit current vs temperature output swing vs output current, single 5v supply
ltc1250 6 1250fb + c f r in 1250 f02 ltc1250 r f c p input capacitance and compensation the large input transistors create a parasitic 55pf capaci- tance from each input to v + . this input capacitance will react with the external feedback resistors to form a pole which can affect amplifier stability. in low gain, high impedance configurations, the pole can land below the unity-gain frequency of the feedback network and degrade phase margin, causing ringing, oscillation, and other unpleasantness. this is true of any op amp, however, the 55pf capacitance at the ltc1250? inputs can affect input noise the ltc1250, like all cmos amplifiers, exhibits two types of low frequency noise: thermal noise and 1/f noise. the ltc1250 uses several design modifications to minimize these noise sources. thermal noise is minimized by rais- ing the g m of the front-end transistors by running them at high bias levels and using large transistor geometries. 1/f noise is combated by optimizing the zero-drift nulling loop to run at twice the 1/f corner frequency, allowing it to reduce the inherently high cmos 1/f noise to near thermal levels at low frequencies. the resultant noise spectrum is quite low at frequencies below the internal 5khz clock frequency, approaching the best bipolar op amps at 10hz and surpassing them below 1hz (figure 1). all this is accomplished in an industry-standard pinout; the ltc1250 requires no external capacitors, no nulling or clock sig- nals, and conforms to industry-standard 8-pin dip and 8-pin so packages. u s a o pp l ic at i wu u i for atio stability with a feedback network impedance as low as 1.9k. this effect can be eliminated by adding a capacitor across the feedback resistor, adding a zero which cancels the input pole (figure 2). the value of this capacitor should be: c pf a f v 55 where a v = closed-loop gain. note that c f is not dependent on the value of r f . circuits with higher gain (a v > 50) or low loop impedance should not require c f for stability. figure 2. c f cancels phase shift due to parasitic c p figure 1. voltage noise vs frequency frequency (hz) 20 voltage noise (nv/ hz) 30 40 50 80 0.01 1 ltc1250 f01 0 0.1 70 60 10 v s = 5v r s = 10 ? ltc1250 op-07 op-27 larger values of c f , commonly used in band-limited dc circuits, may actually increase low frequency noise. the nulling circuitry in the ltc1250 closes a loop that includes the external feedback network during part of its cycle. this loop must settle to its final value within 150 s or it will not fully cancel the 1/f noise spectrum and the low frequency noise of the part will rise. if the loop is underdamped (large r f , no c f ) it will ring for more than 150 s and the noise and offset will suffer. the solution is to add c f as above but beware! too large a value of c f will overdamp the loop, again preventing it from reaching a final value by the 150 s deadline. this condition doesn? affect the ltc1250? offset or output stability, but 1/f noise begins to rise. as a rule of thumb, the r f c f feedback pole should be 7khz (1/150 s, the frequency at which the loop settles) for best 1/f perfor- mance; values between 100pf and 500pf work well with feedback resistors below 100k. this ensures adequate gain at 7khz for the ltc1250 to properly null. high value feedback resistors (above 1m) may require experimenta- tion to find the correct value because parasitics, both in the
ltc1250 7 1250fb + ltc1250 47k r f c f 0.01 1250 f04 + r in 1250 f03 ltc1250 r f ltc1250 and on the pc board, play an increasing role. low value resistors (below 5k) may not require a capaci- tor at all. input bias current the inputs of the ltc1250, like all zero-drift op amps, draw only small switching spikes of ac bias current; dc leakage current is negligible except at very high tempera- tures. the large front-end transistors cause switching spikes 3 to 4 times greater than standard zero-drift op amps: the 50pa bias current spec is still many times better than most bipolar parts. the spikes don? match from one input pin to the other, and are sometimes (but not always) of opposite polarity. as a result, matching the impedances at the inputs (figure 3) will not cancel the bias current, and may cause additional errors. don? do it. when the ltc1250? output is heavily loaded, the chip may dissipate substantial power, raising the temperature of the package and aggravating thermocouples at the inputs. although the ltc1250 will maintain its specified accuracy under these conditions, care must be taken in the layout to prevent or compensate circuit errors. be especially careful of air currents when measuring low frequency noise; nearby moving objects (like people) can create very large noise peaks with an unshielded circuit board. for more detailed explanations and advice on how to avoid these errors, see the ltc1051/ltc1053 data sheet. sampling behavior the ltc1250? zero-drift nulling loop samples the input at 5khz, allowing it to process signals below 2khz with no aliasing. signals above this frequency may show aliasing behavior, although wideband internal circuitry generally keeps errors to a minimum. the output of the ltc1250 will have small spikes at the clock frequency and its harmonics; these will vary in amplitude with different feedback configurations. low frequency or band-limited systems should not be affected, but systems with higher bandwidth (oversampling a/ds, for example) may need to filter out these clock artifacts. output spikes can be minimized with a large feedback capacitor, but this will adversely affect noise performance (see input capaci- tance and compensation on the previous page). applica- tions which require spike-free output in addition to mini- mum noise will need a low-pass filter after the ltc1250; a simple rc will usually do the job (figure 4). the ltc1051/ltc1053 data sheet includes more information about zero-drift amplifier sampling behavior. figure 3. extra resistor will not cancel bias current errors u s a o pp l ic at i wu u i for atio output drive the ltc1250 includes an enhanced output stage which provides nearly symmetrical output source/sink currents. this output is capable of swinging a minimum of 4v into a 1k load with 5v supplies, and can sink or source >20ma into low impedance loads. lightly loaded (r l 100k), the ltc1250 will swing to within millivolts of either rail. in single supply applications, it will typically swing 4.3v into a 1k load with a 5v supply. minimizing external errors the input noise, offset voltage, and bias current specs for the ltc1250 are all well below the levels of circuit board parasitics. thermocouples between the copper pins of the ltc1250 and the tin/lead solder used to connect them can overwhelm the offset voltage of the ltc1250, especially if a soldering iron has been around recently. note also that figure 4. rc output pole limits bandwidth to 330hz
ltc1250 8 1250fb u s a o pp l ic at i wu u i for atio single supply operation the ltc1250 will operate with single supply voltages as low as 4.5v, and the output swings to within millivolts of either supply when lightly loaded. the input stage will common mode to within 250mv of ground with a single 5v supply, and will common mode to ground with single supplies above 11v. most bridge transducers bias their inputs above ground when powered from single supplies, allowing them to interface directly to the ltc1250 in single supply applications. single-ended, ground-refer- enced signals will need to be level shifted slightly to interface to the ltc1250? inputs. fault conditions the ltc1250 is designed to withstand most external fault conditions without latch-up or damage. however, unusu- ally severe fault conditions can destroy the part. all pins are protected against faults of 25ma or 5v beyond either supply, whichever comes first. if the external circuitry can exceed these limits, series resistors or voltage clamp diodes should be included to prevent damage. the ltc1250 includes internal protection against esd damage. all data sheet parameters are maintained to 1kv esd on any pin; beyond 1kv, the input bias and offset currents will increase, but the remaining specs are unaf- fected and the part remains functional to 5kv at the input pins and 8kv at the output pin. extreme esd conditions should be guarded against by using standard antistatic precautions.
ltc1250 9 1250fb j8 0694 0.014 ?0.026 (0.360 ?0.660) 0.200 (5.080) max 0.015 ?0.060 (0.381 ?1.524) 0.125 3.175 min 0.100 0.010 (2.540 0.254) 0.300 bsc (0.762 bsc) 0.008 ?0.018 (0.203 ?0.457) 0 ?15 0.385 0.025 (9.779 0.635) 0.005 (0.127) min 0.405 (10.287) max 0.220 ?0.310 (5.588 ?7.874) 12 3 4 87 65 0.025 (0.635) rad typ 0.045 ?0.068 (1.143 ?1.727) full lead option 0.023 ?0.045 (0.584 ?1.143) half lead option corner leads option (4 plcs) 0.045 ?0.068 (1.143 ?1.727) note: lead dimensions apply to solder dip/plate or tin plate leads. package descriptio u j8 package 8-lead cerdip (narrow .300 inch, hermetic) (reference ltc dwg # 05-08-1110) obsolete package
ltc1250 10 1250fb 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 package descriptio u n8 package 8-lead pdip (narrow .300 inch) (reference ltc dwg # 05-08-1510)
ltc1250 11 1250fb 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. s8 package 8-lead plastic small outline (narrow .150 inch) (reference ltc dwg # 05-08-1610) .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) package descriptio u
ltc1250 12 1250fb + 5v type k ? r4 1m 0.1% c1 100pf 7 6 4 3 2 ?v v out 100mv/ c 1250 ta04 ltc1250 r5 3k r6 7.5k 1% r7 500 ? full-scale trim r9 33k ?v c2 100pf + r3 1m 0.1% r8 5k 1% 5v gnd v in v out lt1025 10mv/ c r1 10k 0.1% r2 10k 0.1% v cm ? for best accuracy, thermocouple resistance should be less than 100 ? + 15v 7 6 4 3 2 10ppm error at 15ma 1 v p-p output noise 2.5 v/ c drift (due to lm399) 1250 ta03 ltc1250 7.5k lm399 31 2 4 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 1994 u s a o pp l ic at i ty p i ca l reference buffer differential thermocouple amplifier lt/gp 0205 1k rev b ? printed in usa related parts part number description comments ltc1050/ltc1051/ single/dual/quad precision zero-drift op amp v os max = 5 v, v supply max = 16.5v ltc1053 ltc1150/ltc1151 single/dual 15v zero-drift op amp high voltage operation ltc2050/ltc2051/ single/dual/quad zero-drift op amp single supply 2.7v to =/?v, sot-23/ms8/gn16 package ltc2052 ltc2053 zero-drift instrumentation amp rail-rail, ms8, 116db, two resistors set gain ltc2054/ltc2055 single/dual zero-drift op amp 150 a per amplifier (max), sot-23/ms8 package ltc6800 rail-to-rail input/output instrumentation amp low cost, single supply, ms8, two resistors set gain

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