Datasheet

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LT1025

1025fb

DESCRIPTIO

APPLICATIO S

■

80µA Supply Current

■

4V to 36V Operation

■

0.5°C Initial Accuracy (A Version)

■

Compatible with Standard Thermocouples

(E, J, K, R, S, T)

■

Auxiliary 10mV/°C Output

■

Available in 8-Lead PDIP and SO Packages

■

Thermocouple Cold Junction Compensator

■

Centigrade Thermometer

■

Temperature Compensation Network

Micropower Thermocouple

Cold Junction Compensator

Type K 10mV/°C Thermometer

The LT

1025 is a micropower thermocouple cold junction

compensator for use with type E, J, K, R, S, and T

thermocouples. It utilizes wafer level and post-package

trimming to achieve 0.5°C initial accuracy. Special curvature

correction circuitry is used to match the “bow” found in all

thermocouples so that accurate cold junction compensation

is maintained over a wider temperature range.

The LT1025 will operate with a supply voltage from 4V to 36V.

Typical supply current is 80µA, resulting in less than 0.1°C

internal temperature rise for supply voltages under 10V.

A 10mV/°C output is available at low impedance, in addition

to the direct thermocouple voltages of 60.9µV/°C (E),

51.7µV/°C (J), 40.3µV/°C (K, T) and 5.95µV/°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.

–

BOW*

CORRECTION

VOLTAGE

BUFFER

GND

E 60.9µV/°C

10mV/°C

–

COMMON

J 51.7µV/°C

K,T 40.6µV/°C

R, S 6µV/°C

10mV/°C

TEMPERATURE

SENSOR

*CORRECTS FOR BOW

COLD JUNCTION,

NOT

IN PROBE (HOT JUNCTION)

LT1025 • BD01

–

LTKA0x

††

TYPE K

R4*

1% C2

0.1µF

–+

100Ω

FULL-SCALE TRIM

OUT

10mV/°C

R3**

255k

–

30µA

–

GND

–

LT1025

*R4 ≤ , R4 IS NOT REQUIRED

(OPEN) FOR LT1025 TEMPERATURES ≥ 0°C

**SELECTED FOR 0°C TO 100°C RANGE

††

OR EQUIVALENT. SEE

“AMPLIFIER CONSIDERATIONS”

LT1025 • TA01

FEATURES

, LTC and LT are registered trademarks of Linear Technology Corporation.

BLOCK DIAGRA

TYPICAL APPLICATIO

Summary of content (12 pages)

PAGE 1
LT1025 Micropower Thermocouple Cold Junction Compensator U FEATURES ■ ■ ■ ■ ■ ■ DESCRIPTIO 80µA Supply Current 4V to 36V Operation 0.
PAGE 2
LT1025 W W W AXI U U U W PACKAGE/ORDER I FOR ATIO U ABSOLUTE RATI GS (Note 1) Input Supply Voltage .......................................... 36V Output Voltage (Forced)........................................ 5V Output Short-Circuit Duration ..................... Indefinite Operating Temperature Range LT1025AC, LT1025C ............................0°C to 70°C LT1025AM, LT1025M .................. – 55°C to 125°C Storage Temperature Range ............
PAGE 3
LT1025 U W TYPICAL PERFOR A CE CHARACTERISTICS 10mV/°C Output Temperature Error LT1025A Supply Current 10 5 200 8 4 180 4 GUARANTEED LIMITS* LT1025 2 0 –2 –4 –6 –8 –10 50 25 0 75 100 –50 –25 JUNCTION TEMPERATURE (°C) 125 GUARANTEED LIMITS* LT1025A 3 2 140 1 0 –1 100 80 60 –3 40 –4 20 –5 50 25 0 75 100 –50 –25 JUNCTION TEMPERATURE (°C) TJ = 125°C 120 –2 LT1025 • G01 TJ = 25°C TJ = –55°C PIN 4 TIED TO PIN 5 125 0 0 10 15 20 25 30 SUPPLY VOLTAGE (V) 5 LT1025 • G02 35 40 LT10
PAGE 4
LT1025 U W U U APPLICATIO S I FOR ATIO an extender made of matching thermocouple wire can be used. This shifts the cold junction from the user termination to the end of the extender so that the LT1025 can be located remotely from the user termination as shown in Figure 2. LT1025 Fe Fe Cu CN CN EXTENDER Cu AMPLIFIER “HOT” JUNCTION FRONT PANEL CONNECTOR “NEW” COLD JUNCTION temperatures below zero unless an external pull-down resistor is added to the VO output.
PAGE 5
LT1025 U W U U APPLICATIO S I FOR ATIO same temperature, but temperature gradients exist within IC packages and across PC boards whenever power is dissipated. For this reason, extreme care must be used to ensure that no temperature gradients exist in the vicinity of the thermocouple terminations, the LT1025, or the thermocouple amplifier.
PAGE 6
LT1025 U W U U APPLICATIO S I FOR ATIO Suggested Amplifier Types SUPPLY VOLTAGE THERMOCOUPLE E, J, K, T R, S ±15V ±5V SINGLE SUPPLY LTKA0x LT1012 LT1001 LTKA0x LT1012 LT1001 LTC1050 LTC1052 LT1006 LTC1050 LTC1052 LT1006 LTC1050 LTC1052 LTKA0x LTC1050 LTC1052 LT1006 LTKA0x LT1012 ERROR TYPE E AND T (°C) 0 K→SCALE 1 5 2 J→SCALE 7.5 3 10 4 12.5 5 SCALE←E 15 6 7 17.5 20 8 SCALE←T 0 50 100 150 200 250 300 350 400 TEMPERATURE (°C) LT1025 • G04 Figure 4.
PAGE 7
LT1025 U W U U APPLICATIO S I FOR ATIO is to calibrate at 1/6 or 5/6 of span. This may be modified if best accuracy is desired at one particular point. 3. Calibrate output by adding in a true offset term which does not affect gain (by summing, etc.). Calibration may be done at any temperature either by immersing the thermocouple in a calibrated bath or by substituting a precision input voltage.
PAGE 8
LT1025 U TYPICAL APPLICATIO S Differential Thermocouple Amplifier C1* R3 1M 0.1% R1 10k 0.1% V+ – VOUT 10mV/°C LTKA0x†† V– 10mV/°C R8 5k 1% + + – R6 7.5k 1% R2 10k 0.1% TYPE K † VCM 5V** R4 1M 0.1% R5 3k VIN VO LT1025 GND R7 500 FULL-SCALE TRIM C2* – R9 = (V )(10k) 100k VOUT (MAX) 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.
PAGE 9
LT1025 U TYPICAL APPLICATIO S Type S Thermocouple Amplifier with Ultralow Offset and Drift † R2** 100Ω FULL-SCALE TRIM R3 909k 1% R4 0.1µF 2.7k R1 1k 1% V+ VIN R,S – + LT1025 GND 15V 7 V+ 5 LT1052 – 3 + V4 1 0.1µF 2 R– 1µF VO TYPE S R7 750k R4 1.37M 1% 6 8 VOUT 10mV/°C 800°C TO 1200°C 0.1µF R5* 10k OFFSET TRIM R6 12k –15V – LT1009 2.5V LT1025 • TA06 * TRIM R5 FOR VOUT = 1.669V AT VIN = 0.000mV (+INPUT OF AMPLIFIER GROUNDED) ** TRIM R2 FOR VOUT = 9.
PAGE 10
LT1025 U PACKAGE DESCRIPTIO J8 Package 8-Lead CERDIP (Narrow 0.300, Hermetic) (LTC DWG # 05-08-1110) CORNER LEADS OPTION (4 PLCS) .023 – .045 (0.584 – 1.143) HALF LEAD OPTION .045 – .068 (1.143 – 1.650) FULL LEAD OPTION .005 (0.127) MIN .405 (10.287) MAX 8 7 6 5 .025 (0.635) RAD TYP .220 – .310 (5.588 – 7.874) 1 2 .300 BSC (7.62 BSC) 3 4 .200 (5.080) MAX .015 – .060 (0.381 – 1.524) .008 – .018 (0.203 – 0.457) 0° – 15° NOTE: LEAD DIMENSIONS APPLY TO SOLDER DIP/PLATE OR TIN PLATE LEADS .
PAGE 11
LT1025 U PACKAGE DESCRIPTIO N8 Package 8-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) .300 – .325 (7.620 – 8.255) ( +0.889 8.255 –0.381 .130 ± .005 (3.302 ± 0.127) .045 – .065 (1.143 – 1.651) .065 (1.651) TYP .008 – .015 (0.203 – 0.381) +.035 .325 –.015 .400* (10.160) MAX 8 7 6 1 2 3 5 .255 ± .015* (6.477 ± 0.381) ) .120 (3.048) .020 MIN (0.508) MIN .018 ± .003 (0.457 ± 0.076) .100 (2.54) BSC 4 N8 1002 NOTE: 1.
PAGE 12
LT1025 U TYPICAL APPLICATIO Grounded Thermocouple Amplifier with Positive Output R1 10k 1% + R3 1M 1% R5 FULL-SCALE 2k ADJUST – TYPE J* V R4 10k C1 0.01µF + R6** 8.4k V+ VIN – LT1025 GND R– R7 6.8k J C2 0.01µF LTKA0x†† VOUT 10mV/°C + V– LT1025 • TA07 * FOR BEST ACCURACY, THERMOCOUPLE RESISTANCE SHOULD BE LESS THAN 50Ω ** SELECTED FOR 0°C TO 200°C RANGE †† OR EQUIVALENT.