LINEAR LT1025CJ8

LT1025 Micropower Thermocouple Cold Junction Compensator FEATURES DESCRIPTIO ® n80mA Supply Current The LT 1025 is a micropower thermocouple cold junction n4V to 36V Operation compensator for use with type E, J, K, R, S, and T n0.5°C Initial Accuracy (A Version) thermocouples. It utilizes wafer level and post-package nCompatible with Standard Thermocouples trimming to achieve 0.5°C initial accuracy. Special curvature (E, J, K, R, S, T) correction circuitry is used to match the “bow” found in all nAuxiliary 10mV/°C Output thermocouples so that accurate cold junction compensation nAvailable in 8-Lead PDIP and SO Packages is maintained over a wider temperature range. The LT1025 will operate with a supply voltage from 4V to 36V. U Typical supply current is 80mA, resulting in less than 0.1°C APPLICATIO S internal temperature rise for supply voltages under 10V. nThermocouple Cold Junction Compensator A 10mV/°C output is available at low impedance, in addition nCentigrade Thermometer to the direct thermocouple voltages of 60.9mV/°C (E), nTemperature Compensation Network 51.7mV/°C (J), 40.3mV/°C (K, T) and 5.95mV/°C (R, S). All outputs are essentially independent of power supply voltage. A special kit is available (LTK001) which contains an LT1025 and a custom tailored thermocouple amplifier. The amplifier and compensator are matched to allow a much tighter specifi- cation of temperature error than would be obtained by adding the compensator and amplifier errors on a worst-case basis. The amplifier from this kit is available separately as LTKA0x. The LT1025 is available in either an 8-pin PDIP or 8-pin SO package for temperatures between 0°C and 70°C. , LTC and LT are registered trademarks of Linear Technology Corporation. BLOCK DIAGRA TYPICAL APPLICATIO Type K 10mV/°C Thermometer E 60.9μV/°C R2 R3** 100Ω 255k V IN J 51.7μV/°C FULL-SCALE TRIM 1% + R1 BUFFER K,T 40.6μV/°C BOW* + 1k V – – CORRECTION + 1% C2 V VOLTAGE – 0.1μF R, S 6μV/°C V OUT †† LTKA0x 10mV/°C V 10mV/°C IN K + –+ TEMPERATURE – V – R COMMON *R4 ≤ , R4 IS NOT REQUIRED SENSOR LT1025 – 30μA V (OPEN) FOR LT1025 TEMPERATURES ‡ 0°C TYPE K V 10mV/°C V – 0 O C1 GND R **SELECTED FOR 0°C TO 100°C RANGE 0.1μF R4* GND *CORRECTS FOR BOW †† OR EQUIVALENT. SEE IN COLD JUNCTION, NOT “AMPLIFIER CONSIDERATIONS” – IN PROBE (HOT JUNCTION) LT1025 • BD01 V LT1025 • TA01 1025fb 1 U W U LT1025 UU W ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) TOP VIEW ORDER PART Input Supply Voltage .......................................... 36V E J 1 NUMBER 8 60.9μV/°C 51.7μV/°C Output Voltage (Forced)........................................ 5V K, T V 2 7 IN 40.6μV/°C Output Short-Circuit Duration ..................... Indefinite LT1025ACN8 V R, S O 3 6 Operating Temperature Range 10mV/°C 6μV/°C LT1025CN8 – R 4 5 GND COMMON LT1025AC, LT1025C ............................0°C to 70°C LT1025CS8 N8 PACKAGE S8 PACKAGE LT1025AM, LT1025M .................. – 55°C to 125°C 8-LEAD PDIP 8-LEAD PLASTIC SO S8 PART MARKING Storage Temperature Range ............ – 55°C to 150°C T = 150°C, q = 130°C/W (N8) JMAX JA 1025 T = 150°C, q = 190°C/W (S8) JMAX JA J8 PACKAGE 8-LEAD CERDIP LT1025AMJ8 T = 150°C, q = 100°C/W JMAX JA LT1025MJ8 OBSOLETE PACKAGE Consider the N8 Package for Alternate Source Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specificatons are at T = 25°C. V = 5V, Pin 5 tied to Pin 4, unless otherwise noted. A S PARAMETER CONDITIONS MIN TYP MAX UNITS Temperature Error at T = 25°C J 10mV/°C Output (Notes 4, 5) LT1025A 0.3 0.5 °C LT1025 0.5 2.0 °C Full Temperature SpanlSee Curve Resistor Divider Accuracy V = 10mV/°C OUT (Notes 2, 4) LT1025A E 60.6 60.9 61.3mV/°C J 51.4 51.7 52.1mV/°C K, T 40.3 40.6 41.0mV/°C R, S 5.8 5.95 6.2mV/°C LT1025 E 60.4 60.9 61.6mV/°C J 51.2 51.7 52.3mV/°C K, T 40.2 40.6 41.2mV/°C R, S 5.75 5.95 6.3mV/°C Supply Current 4V £ V 36V 50 80 100mA IN £ LT1025AC, LT1025Cl50 150mA LT1025AM, LT1025Ml200mA Line Regulation (Note 3) 4V £ V 36Vl0.003 0.02 °C/V IN £ Load Regulation (Note 3) 0 £ I 1mAl0.04 0.2 °C O £ Divider Impedance E 2.5 kW J 2.1 kW K, T 4.4 kW R, S 3.8 kW Change in Supply Current 4V £ V 36V 0.01 0.05mA/V IN £ Note 1: Absolute Maximum Ratings are those values beyond which the Note 4: To calculate total temperature error at individual thermocouple life of a device may be impaired. outputs, add 10mV/°C output error to the resistor divider error. Total error for type K output at 25°C with an LT1025A is 0.5°C plus (0.4mV/°C)(25°C)/ Note 2: Divider accuracy is measured by applying a 10.000V signal to the (40.6mV/°C) = 0.5°C + 0.25°C = 0.75°C. output divider and measuring the individual outputs. Note 5: Temperature error is defined as the deviation from the following Note 3: Regulation does not include the effects of self-heating. See -4 2 formula: V = 10mV(T) + (10mV)(5.5 • 10 )(T – 25°C) . The second “Internal Temperature Rise” in Application Guide. Load regulation is OUT term is a built-in nonlinearity designed to help compensate the nonlinearity 30mA £ I 1mA for T 0°C. O £A £ of the cold junction. This “bow” is »0.34°C for a 25°C temperature change. 1025fb 2 U WW W LT1025 TYPICAL PERFOR A CE CHARACTERISTICS 10mV/°C Output Temperature 10mV/°C Output Temperature Error LT1025 Error LT1025A Supply Current 10 5 200 DOES NOT INCLUDE 30μA 8 4 180 PULL-DOWN CURRENT REQUIRED FOR TEMPERATURES GUARANTEED LIMITS* GUARANTEED LIMITS* 6 3 160 BELOW 0°C LT1025 LT1025A 4 2 140 T = 125°C J 2 1m120 0 0 100 –2 –1 80 T = 25°C J –4 –2 60 –6 –3 40 T = –55°C J –8 –4 20 PIN 4 TIED TO PIN 5 –10 –5 0 –50 0 25 50 75 100 125 –50 0 25 50 75 100 125 35 –25 –25 051 105 20 25 30 40 JUNCTION TEMPERATURE (°C) JUNCTION TEMPERATURE (°C) SUPPLY VOLTAGE (V) LT1025 • G01 LT1025 • G02 LT1025 • G03 *ERROR CURVE FACTORS IN THE NONLINEARITY *ERROR CURVE FACTORS IN THE NONLINEARITY TERM BUILT IN TO THE LT1025. SEE THEORY OF TERM BUILT IN TO THE LT1025. SEE THEORY OF OPERATION IN APPLICATION GUIDE SECTION OPERATION IN APPLICATION GUIDE SECTION APPLICATIO S I FOR ATIO The LT1025 was designed to be extremely easy to use, but To date, IC manufacturers efforts to make microminiature the following ideas and suggestions should be helpful in thermos bottles have not been totally successful. There- obtaining the best possible performance and versatility fore, an electronically simulated cold-junction is required from this new cold junction compensator. for most applications. The idea is basically to add a temperature dependent voltage to V such that the voltage S Theory of Operation sum is the same as if the T2 junction were at a constant 0°C instead of at room temperature. This voltage source is A thermocouple consists of two dissimilar metals joined called a cold junction compensator. Its output is designed together. A voltage (Seebeck EMF) will be generated if the to be 0V at 0°C and have a slope equal to the Seebeck two ends of the thermocouple are at different coefficient over the expected range of T2 temperatures. temperatures. In Figure 1, iron and constantan are joined at the temperature measuring point T1. Two additional Fe Cu T1 TEMPERATURE thermocouple junctions are formed where the iron and T2 V S TO BE MEASURED } constantan connect to ordinary copper wire. For the CONSTANTAN Cu LT1025 MUST BE LOCATED purposes of this discussion it is assumed that these two NEXT TO COLD JUNCTION junctions are at the same temperature, T2. The Seebeck FOR TEMPERATURE TRACKING LT1025 • AG01 voltage, V , is the product of the Seebeck coefficient a, S Figure 1 and the temperature difference, T1 – T2; V = a (T1 – T2). S The junctions at T2 are commonly called the cold junction To operate properly, a cold junction compensator must be because a common practice is to immerse the T2 junction at exactly the same temperature as the cold junction of the in 0°C ice/water slurry to make T2 independent of room thermocouple (T2). Therefore, it is important to locate the temperature variations. Thermocouple tables are based LT1025 physically close to the cold junction with local on a cold-junction temperature of 0°C. temperature gradients minimized. If this is not possible, 1025fb 3 TEMPERATURE ERROR (°C) TEMPERATURE ERROR (°C) CURRENT ( A) UUWU UW LT1025 APPLICATIO S I FOR ATIO temperatures below zero unless an external pull-down an extender made of matching thermocouple wire can be used. This shifts the cold junction from the user termina- resistor is added to the V output. This resistor can be O connected to any convenient negative supply. It should be tion to the end of the extender so that the LT1025 can be selected to sink at least 30mA of current. Suggested value located remotely from the user termination as shown in Figure 2. for a – 5V supply is 150kW, and for a – 15V supply, 470kW. Smaller resistors must be used if an external load is LT1025 connected to the 10mV/°C output. The LT1025 can source AMPLIFIER up to 1mA of current, but there is a trade-off with internal Fe Fe Cu “HOT” temperature rise. JUNCTION CN CN Cu EXTENDER Internal Temperature Rise FRONT PANEL “NEW” COLD CONNECTOR JUNCTION LT1025 • AG02 The LT1025 is specified for temperature accuracy assum- ing no internal temperature rise. At low supply voltages Figure 2 this rise is usually negligible (» 0.05°C at 5V), but at higher The four thermocouple outputs on the LT1025 are supply voltages or with external loads or pull-down cur- 60.9mV/°C (E), 51.7mV/°C (J), 40.6mV/°C (K and T), and rent, internal rise could become significant. This effect can 6mV/°C (R and S). These particular coefficients are chosen be calculated from a simple thermal formula, DT = (q) JA to match the room temperature (25°C) slope of the + (V )(I + I ), where qis thermal resistance from junction Q L JA thermocouples. Over wide temperature ranges, however, + to ambient, (»130°C/W), V is the LT1025 supply voltage, the slope of thermocouples changes, yielding a quasi- I is the LT1025 supply current (»80mA) and I is the total Q L parabolic error compared to a constant slope. The LT1025 load current including actual load to ground and any pull- outputs have a deliberate parabolic “bow” to help down current needed to generate negative outputs. A compensate for this effect. The outputs can be mathemati- sample calculation with a 15V supply and 50mA pull-down cally described as the sum of a linear term equal to room current would yield, (130°C/W) (15V) (80mA + 50mA) = temperature slope plus a quadratic term proportional to 0.32°C. This is a significant rise in some applications. It temperature deviation from 25°C squared. The coefficient can be reduced by lowering supply voltage (a simple fix is (ß) of the quadratic term is a compromise value chosen to lead) or the system can be to insert a 10V zener in the V IN offer improvement in all the outputs. calibrated and specified after an initial warm-up period of 2 V = aT + aß(T –25°) several minutes. OUT – 4 ß » 5.5 • 10 Driving External Capacitance The actual ß term which would be required to best The direct thermocouple drive pins on the LT1025 (J, K, compensate each thermocouple type in the temperature etc.) can be loaded with as much capacitance as desired, –4 –4 range of 0°C to 50°C is: E, 6.6 • 10 ; J, 4.8 • 10 ; but the 10mV/°C output should not be loaded with more –4 –3 –3 –3 K, 4.3 • 10 ; R, 1.9 • 10 , S, 1.9 • 10 ; T, 1 • 10 . than 50pF unless external pull-down current is added, or The temperature error specification for the LT1025 a compensation network is used. 10mV/°C output (shown as a graph) assumes a ß of –4 Thermocouple Effects in Leads 5.5 •10 . For example, an LT1025 is considered “perfect” if its 10mV/°C output fits the equation V = 10mV(T) + O Thermocouple voltages are generated whenever dissimi- –4 2 (10mV)(5.5 • 10 )(T – 25°C) . lar materials are joined. This includes the leads of IC packages, which may be kovar in TO-5 cans, alloy 42 or Operating at Negative Temperatures copper in dual-in-line packages, and a variety of other The LT1025 is designed to operate with a single positive materials in plating finishes and solders. The net effect supply. It therefore cannot deliver proper outputs for of these thermocouples is “zero” if all are at exactly the 1025fb 4 UUWU LT1025 APPLICATIO S I FOR ATIO same temperature, but temperature gradients exist within now be forced by feedback to generate –10mV/°C as long IC packages and across PC boards whenever power is as the grounded output is supplying a net “source” current dissipated. For this reason, extreme care must be used to into ground. This condition is satisfied by selecting R1 – ensure that no temperature gradients exist in the vicinity such that the current through R1 (I ) is more than the sum of the thermocouple terminations, the LT1025, or the of the LT1025 supply current, the maximum load current thermocouple amplifier. If a gradient cannot be eliminated, (I ), and the minimum zener current (»50mA). R2 is then L – leads should be positioned isothermally, especially the selected to supply more current than I . – LT1025 R and appropriate output pins, the amplifier input ± + V VV±(»6V) Z pins, and the gain setting resistor leads. An effect to watch R1= , R2 = ± for is amplifier offset voltage warm-up drift caused by 300m+AI VR / 1+m 280 A L mismatched thermocouple materials in the wire-bond/ For –15V supplies, with I = 20mA maximum, R1 = 47k and L lead system of the IC package. This effect can be as high R2 = 15k. as tens of microvolts in TO-5 cans with kovar leads. It has nothing to do with the actual offset drift specification of the Amplifier Considerations amplifier and can occur in amplifiers with measured “zero” drift. Warm-up drift is directly proportional to amplifier Thermocouple amplifiers need very low offset voltage and power dissipation. It can be minimized by avoiding TO-5 drift, and fairly low bias current if an input filter is used. The cans, using low supply current amplifiers, and by using the best precision bipolar amplifiers should be used for type lowest possible supply voltages. Finally, it can be accom- J, K, E, and T thermocouples which have Seebeck coeffi- modated by calibrating and specifying the system after a cients of 40mV/°C to 60mV/°C. In particularly critical appli- five minute warm-up period. cations or for R and S thermocouples (6mV/°C to 15mV/°C), a chopper-stabilized amplifier is required. Linear Technol- Reversing the Polarity of the 10mV/°C Output ogy offers three amplifiers specifically tailored for thermo- couple applications. The LTKA0x is a bipolar design with The LT1025 can be made to “stand on its head” to achieve extremely low offset (< 35mV), low drift (<1.5mV/°C), very a minus 10mV/°C output point. This is done as shown in low bias current (<1nA), and almost negligible warm-up Figure 3. The normal output (V ) is grounded and feed- O drift (supply current is »400mA). It is very cost effective back is established between the ground pin and the even when compared with “jellybean” op amps with vastly positive supply pin by feeding both of them with currents inferior specifications. while coupling them with a 6V zener. The ground pin will For the most demanding applications, the LTC1050 and + V (15V) LTC1052 CMOS chopper-stabilized amplifiers offer 5mV + R2 I offset and 0.05mV/°C drift (even over the full military 15k temperature range). Input bias current is 30pA, and gain is typically 30 million. These amplifiers should be used for V IN R and S thermocouples, especially if no offset adjust- V O LT1025 ments can be tolerated, or a large ambient temperature D1 V ≈ 6V Z swing is expected. GND Regardless of amplifier type, it is suggested that for best V OUT –10mV/°C possible performance, dual-in-line (DIP) packages be – R1 I used to avoid thermocouple effects in the kovar leads of I R L L 47k TO-5 metal can packages if amplifier supply current ex- – V (–15V) ceeds 500mA. These leads can generate both DC and AC LT1025 • AG03 offset terms in the presence of thermal gradients in the Figure 3 package and/or external air motion. 1025fb 5 UUWU ERROR TYPE J AND K (°C) LT1025 APPLICATIO S I FOR ATIO In many situations, thermocouples are used in high noise 0 KfiSCALE 0 environments, and some sort of input filter is required. 2.5 1 (See discussion of input filters). To reject 60Hz pick-up 5 2 with reasonable capacitor values, input resistors in the JfiSCALE 7.5 3 10k-100k range are needed. Under these conditions, bias 10 4 current for the amplifier needs to be less than 1nA to avoid 12.5 5 SCALE‹E offset and drift effects. 15 6 17.5 7 To avoid gain error, high open loop gain is necessary for 20 8 SCALE‹T single-stage thermocouple amplifiers with 10mV/°C or higher outputs. A type K amplifier, for instance, with 100mV/°C 0 50 100 150 200 250 300 350 400 TEMPERATURE (°C) output, needs a closed loop gain of »2,500. An ordinary op LT1025 • G04 amp with a minimum open loop of 50,000 would have an Figure 4. Thermocouple Nonlinearity, 0°C to 400°C initial gain error of (2,500)/(50,000) = 5%! Although closed loop gain is commonly trimmed, temperature drift of open loop gain will have a very deleterious effect on output ERROR BEFORE OFFSETTING accuracy. Minimum suggested open loop gain for type E, J, K, and T thermocouples is 250,000. This gain is adequate for V H ERROR AFTER OFFSETTING type R and S if output scaling is 10mV/°C or less. OFFSET AMPLIFIER Suggested Amplifier Types SIMPLE AMPLIFIER SUPPLY VOLTAGE THERMOCOUPLE–15V–5V SINGLE SUPPLY THERMOCOUPLE V E, J, K, T LTKA0x LTKA0x LTC1050 L LT1012 LT1012 LTC1052 LT1001 LT1001 LT1006 0 T T1/6 T T5/6 T L M H LTC1050 TEMPERATURE (°C) LTC1052 LT1025 • G05 LT1006 Figure 5. Offset Curve Fitting R, S LTKA0x LTC1050 LTC1050 LT1012 LTC1052 LTC1052 temperature. The temperature range of interest is between T L LTKA0x LT1006 and T , with a calibration point at T . If a simple amplifier is H M used and calibrated at T , the output will be very high at T M L Thermocouple Nonlinearities and very low at T . Adding the proper offset term and H calibrating at T1/6 or T5/6 can significantly reduce errors. The Thermocouples are linear over relatively limited temperature technique is as follows: spans if accuracies of better than 2°C are needed. The graph in Figure 4 shows thermocouple nonlinearity for the 1. Calculate amplifier gain: temperature range of 0°C to 400°C. Nonlinearities can be G = (SF) (T – T )/(V – V ) dealt with in hardware by using offsets, breakpoints, or power H L H L SF = Output scale factor, e.g., 10mV/°C series generators. Software solutions include look-up tables, V = Thermocouple output at T power series expansions, and piece-wise approximations. H H V = Thermocouple output at T For tables and power series coefficients, the reader is referred L L to the ASTM Publication 470A. 2. Use precision resistors to set gain or calibrate gain by introducing a precision “delta” input voltage and trimming Hardware correction for nonlinearity can be as simple as an for proper “delta” output. offset term. This is shown in Figure 5. The thermocouple shown in the figure has an increasing slope (a) with 1025fb 6 ERROR TYPE E AND T (°C) OUTPUT (V) UUWU LT1025 APPLICATIO S I FOR ATIO 3. Calibrate output by adding in a true offset term which is to calibrate at 1/6 or 5/6 of span. This may be modified does not affect gain (by summing, etc.). Calibration may if best accuracy is desired at one particular point. be done at any temperature either by immersing the Breakpoint correction for nonlinearity is more compli- thermocouple in a calibrated bath or by substituting a cated than a simple offset, but a single breakpoint com- precision input voltage. The method which tends to bined with offset will reduce errors typically by 4:1 over a minimize worst-case error over the whole T to T range L H simple offset technique. TYPICAL APPLICATIO S Eliminating Amplifier Feedback Resistors (Output Goes Negative with Increasing Temperature) 15V V IN LT1025 V K O – C1 GND R 300k 0.1μF –15V 15V 2 7 – V 6 OUT †† LTKA0x –10mV/°C 3k 3 + + – 4 C2 –15V 1μF TYPE K †† OR EQUIVALENT. SEE “AMPLIFIER CONSIDERATIONS” Type K Thermometer with Grounded Thermocouple R3 R2 255k + V 100Ω 1% R6 V IN V V OUT 9.1k O 0.1μF 10mV/°C R1 – 1k LT1025 V R4* *R4 ≤ IF OUTPUT MUST SINK CURRENT, R4 1% 30μA 470k + V MUST BE DECREASED APPROPRIATELY. R4 IS NOT – GND R REQUIRED (OPEN) FOR LT1025 TEMPERATURES ‡ 0°C – – WHEN SOURCING CURRENT ONLY V †† †† R5 LTKA0x OR EQUIVALENT. SEE “AMPLIFIER CONSIDERATIONS” –15V 10k + C2 – V 1μF TYPE K 1025fb 7 U UUWU LT1025 TYPICAL APPLICATIO S Differential Thermocouple Amplifier C1* R3 1M 0.1% R1 + 10k V 0.1% – V †† OUT LTKA0x 10mV/°C R6 + 7.5k – + R2 – 1% V † 10k TYPE K R7 0.1% 500 R4 C2* V CM FULL-SCALE 1M 5V** TRIM 0.1% R8 R5 5k 3k V IN 1% 10mV/°C V O – LT1025 (V )(10k) R9 = 100k V (MAX) OUT – GND V –15V *C1 AND C2 FILTER RIPPLE AND NOISE, BUT WILL LIMIT AC COMMON-MODE REJECTION IF NOT MATCHED. SUGGESTED VALUES ARE 0.001μF TO 0.1μF **USE LOWEST POSSIBLE SUPPLY VOLTAGE TO MINIMIZE INTERNAL TEMPERATURE RISE † FOR BEST ACCURACY, THERMOCOUPLE RESISTANCE SHOULD BE LESS THAN 100Ω †† OR EQUIVALENT. SEE “AMPLIFIER CONSIDERATIONS” Utilizing Negative LT1025 Drive to Accommodate Grounded Thermocouple* 15V R7 15k V IN V LT1025 O 6V R1 GND 1k 1% –10mV/°C R2 R4 100Ω R5 15V 141k R3 47k C1 141k – 0.1μF 1% V OUT –15V R6 †† LTKA0x 10mV/°C 10k 0°C TO 500°C + – + 1μF –15V TYPE E *SEE “REVERSING THE POLARITY OF THE 10mV/°C OUTPUT” †† OR EQUIVALENT. SEE “AMPLIFIER CONSIDERATIONS” 1025fb 8 U LT1025 TYPICAL APPLICATIO S † Type S Thermocouple Amplifier with Ultralow Offset and Drift R2** 100Ω R3 FULL-SCALE 909k TRIM 1% R4 R1 0.1μF 2.7k 1k 1% 15V + V 2 7 – + V V OUT 6 5 10mV/°C LT1052 V IN – 8 800°C TO 1200°C 3 V R,S + 4 –+ R4 1 LT1025 1μF 1.37M 0.1μF 0.1μF 1% TYPE S V O – GND R R5* 10k R7 R6 OFFSET 750k 12k TRIM LT1009 –15V 2.5V LT1025 • TA06 * TRIM R5 FOR V = 1.669V AT V = 0.000mV (+INPUT OF AMPLIFIER GROUNDED) OUT IN ** TRIM R2 FOR V = 9.998V AT T = 1000°C, OR FOR V AT +INPUT OF AMPLIFIER = 9.585mV OUT IN † THIS AMPLIFIER HAS A DELIBERATE OFFSET TO ALLOW OUTPUT SLOPE (10mV/°C) TO BE SET INDEPENDENTLY FROM AN ARBITRARY HIGH TEMPERATURE CENTER POINT (1000°C). THIS IS REQUIRED BECAUSE THE SLOPE OF TYPE “S” THERMOCOUPLES VARIES RAPIDLY WITH TEMPERATURE, INCREASING FROM 6μV/°C AT 25°C to 11μV/°C AT 1000°C. NONLINEARITY LIMITS ACCURACY TO ≈3°C OVER THE 800°C TO 1200°C RANGE EVEN WITH OFFSET CORRECTION 1025fb 9 U LT1025 PACKAGE DESCRIPTIO J8 Package 8-Lead CERDIP (Narrow 0.300, Hermetic) (LTC DWG # 05-08-1110) .405 CORNER LEADS OPTION (4 PLCS) (10.287) .005 MAX (0.127) MIN 87 65 .023 – .045 (0.584 – 1.143) HALF LEAD OPTION .025 .220 – .310 .045 – .068 (0.635) (5.588 – 7.874) RAD TYP (1.143 – 1.650) FULL LEAD OPTION 12 3 4 .200 .300 BSC (5.080) (7.62 BSC) MAX .015 – .060 (0.381 – 1.524) .008 – .018 0° – 15° (0.203 – 0.457) .045 – .065 .125 NOTE: LEAD DIMENSIONS APPLY TO SOLDER DIP/PLATE (1.143 – 1.651) 3.175 OR TIN PLATE LEADS MIN .014 – .026 .100 (2.54) (0.360 – 0.660) BSC J8 0801 OBSOLETE PACKAGE 1025fb 10 U LT1025 PACKAGE DESCRIPTIO N8 Package 8-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) .400* (10.160) MAX .130 – .005 .300 – .325 .045 – .065 (1.143 – 1.651) (3.302 – 0.127) (7.620 – 8.255) 87 6 5 .065 .255 – .015* (1.651) (6.477 – 0.381) .008 – .015 TYP .120 (0.203 – 0.381) .020 (3.048) +.035 MIN (0.508) 12 3 4 .325 –.015 MIN .100 .018 – .003 N8 1002 +0.889 (2.54) 8.255 (0.457 – 0.076) () –0.381 BSC NOTE: INCHES 1. DIMENSIONS ARE MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm) S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) .189 – .197 (4.801 – 5.004) .045 –.005 NOTE 3 .050 BSC 7 5 8 6 .245 .160 –.005 MIN .150 – .157 .228 – .244 (3.810 – 3.988) (5.791 – 6.197) NOTE 3 .030 –.005 TYP 1 2 3 4 RECOMMENDED SOLDER PAD LAYOUT .010 – .020 · 45° .053 – .069 (0.254 – 0.508) (1.346 – 1.752) .004 – .010 .008 – .010 (0.101 – 0.254) 0°– 8° TYP (0.203 – 0.254) .016 – .050 .014 – .019 .050 (0.406 – 1.270) (0.355 – 0.483) (1.270) NOTE: TYP BSC INCHES 1. DIMENSIONS IN (MILLIMETERS) 2. DRAWING NOT TO SCALE 3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. SO8 0303 MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm) 1025fb 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. 11 U LT1025 TYPICAL APPLICATIO Grounded Thermocouple Amplifier with Positive Output R4 R1 R3 10k 10k 1M 1% 1% R5 FULL-SCALE + – 2k ADJUST TYPE J* R6** C1 8.4k 0.01μF + V + V V IN – LT1025 V R7 †† OUT LTKA0x 6.8k 10mV/°C J + – GND R – C2 V 0.01μF LT1025 • TA07 * FOR BEST ACCURACY, THERMOCOUPLE RESISTANCE SHOULD BE LESS THAN 50Ω ** SELECTED FOR 0°C TO 200°C RANGE †† OR EQUIVALENT. SEE “AMPLIFIER CONSIDERATIONS” RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1012 Picoamp Input Current Op Amp 120mV Max V , 280pA Max I OS OS LTC1050 Zero Drift Amplifier 5mV Max V , A 1V/mV Max OS VOL LTC2050 SOT-23 Zero Drift Amplifier 3mV Max V OS 1025fb LT/TP 1103 1K REV B • PRINTED IN USA Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 12 l l ª LINEAR TECHNOLOGY CORPORATION 1988 (408) 432-1900 FAX: (408) 434-0507 www.linear.com U