LINER LT1025 Micropower thermocouple cold junction compensator Datasheet

LT1025
Micropower Thermocouple
Cold Junction Compensator
U
FEATURES
■
■
■
■
■
■
DESCRIPTIO
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
U
APPLICATIO S
■
■
■
Thermocouple Cold Junction Compensator
Centigrade Thermometer
Temperature Compensation Network
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 specification 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.
W
U
BLOCK DIAGRA
TYPICAL APPLICATIO
Type K 10mV/°C Thermometer
E 60.9µV/°C
VIN
R2
100Ω
FULL-SCALE TRIM
J 51.7µV/°C
R3**
255k
1%
+
BOW*
CORRECTION
VOLTAGE
BUFFER
10mV/°C
TEMPERATURE
SENSOR
R, S 6µV/°C
V+
R– COMMON
V+
–
LTKA0x††
VIN
K
–
+
LT1025
V0 10mV/°C
GND
*CORRECTS FOR BOW
IN COLD JUNCTION, NOT
IN PROBE (HOT JUNCTION)
R1
1k
1%
K,T 40.6µV/°C
–
GND R–
+
V–
TYPE K
VO
R4*
C1
0.1µF
C2
0.1µF
VOUT
10mV/°C
V–
*R4 ≤ 30µA , R4 IS NOT REQUIRED
(OPEN) FOR LT1025 TEMPERATURES ≥ 0°C
**SELECTED FOR 0°C TO 100°C RANGE
†† OR
LT1025 • BD01
V–
EQUIVALENT. SEE
“AMPLIFIER CONSIDERATIONS”
LT1025 • TA01
1025fb
1
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 ............ – 55°C to 150°C
ORDER PART
NUMBER
TOP VIEW
E
60.9µV/°C 1
VIN 2
VO 3
10mV/°C
GND 4
8
7
6
5
N8 PACKAGE
8-LEAD PDIP
J
51.7µV/°C
K, T
40.6µV/°C
R, S
6µV/°C
R–
COMMON
LT1025ACN8
LT1025CN8
LT1025CS8
S8 PACKAGE
8-LEAD PLASTIC SO
S8 PART MARKING
TJMAX = 150°C, θJA = 130°C/W (N8)
TJMAX = 150°C, θJA = 190°C/W (S8)
1025
LT1025AMJ8
LT1025MJ8
J8 PACKAGE 8-LEAD CERDIP
TJMAX = 150°C, θJA = 100°C/W
OBSOLETE PACKAGE
Consider the N8 Package for Alternate 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, otherwise specificatons are at TA = 25°C. VS = 5V, Pin 5 tied to Pin 4, unless otherwise noted.
PARAMETER
CONDITIONS
Temperature Error at
10mV/°C Output (Notes 4, 5)
TJ = 25°C
LT1025A
LT1025
MIN
Full Temperature Span
Resistor Divider Accuracy
(Notes 2, 4)
VOUT = 10mV/°C
LT1025A
LT1025
TYP
MAX
UNITS
0.3
0.5
0.5
2.0
°C
°C
See Curve
●
E
J
K, T
R, S
60.6
51.4
40.3
5.8
60.9
51.7
40.6
5.95
61.3
52.1
41.0
6.2
µV/°C
µV/°C
µV/°C
µV/°C
E
J
K, T
R, S
60.4
51.2
40.2
5.75
60.9
51.7
40.6
5.95
61.6
52.3
41.2
6.3
µV/°C
µV/°C
µV/°C
µV/°C
50
50
80
100
150
200
µA
µA
µA
°C/V
4V ≤ VIN ≤ 36V
LT1025AC, LT1025C
LT1025AM, LT1025M
●
●
Line Regulation (Note 3)
4V ≤ VIN ≤ 36V
●
0.003
0.02
Load Regulation (Note 3)
0 ≤ IO ≤ 1mA
●
0.04
0.2
Supply Current
Divider Impedance
Change in Supply Current
E
J
K, T
R, S
4V ≤ VIN ≤ 36V
Note 1: Absolute Maximum Ratings are those values beyond which the
life of a device may be impaired.
Note 2: Divider accuracy is measured by applying a 10.000V signal to the
output divider and measuring the individual outputs.
Note 3: Regulation does not include the effects of self-heating. See
“Internal Temperature Rise” in Application Guide. Load regulation is
30µA ≤ IO ≤ 1mA for TA ≤ 0°C.
2.5
2.1
4.4
3.8
0.01
°C
kΩ
kΩ
kΩ
kΩ
0.05
µA/V
Note 4: To calculate total temperature error at individual thermocouple
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 (0.4µV/°C)(25°C)/
(40.6µV/°C) = 0.5°C + 0.25°C = 0.75°C.
Note 5: Temperature error is defined as the deviation from the following
formula: VOUT = 10mV(T) + (10mV)(5.5 • 10-4)(T – 25°C)2. The second
term is a built-in nonlinearity designed to help compensate the nonlinearity
of the cold junction. This “bow” is ≈ 0.34°C for a 25°C temperature change.
1025fb
2
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
LT1025 • G03
*ERROR CURVE FACTORS IN THE NONLINEARITY
TERM BUILT IN TO THE LT1025. SEE THEORY OF
OPERATION IN APPLICATION GUIDE SECTION
U
*ERROR CURVE FACTORS IN THE NONLINEARITY
TERM BUILT IN TO THE LT1025. SEE THEORY OF
OPERATION IN APPLICATION GUIDE SECTION
DOES NOT INCLUDE 30µA
PULL-DOWN CURRENT
REQUIRED FOR TEMPERATURES
BELOW 0°C
160
CURRENT (µA)
6
TEMPERATURE ERROR (°C)
TEMPERATURE ERROR (°C)
10mV/°C Output Temperature
Error LT1025
W
U U
APPLICATIO S I FOR ATIO
The LT1025 was designed to be extremely easy to use, but
the following ideas and suggestions should be helpful in
obtaining the best possible performance and versatility
from this new cold junction compensator.
Theory of Operation
A thermocouple consists of two dissimilar metals joined
together. A voltage (Seebeck EMF) will be generated if the
two ends of the thermocouple are at different
temperatures. In Figure 1, iron and constantan are joined
at the temperature measuring point T1. Two additional
thermocouple junctions are formed where the iron and
constantan connect to ordinary copper wire. For the
purposes of this discussion it is assumed that these two
junctions are at the same temperature, T2. The Seebeck
voltage, VS, is the product of the Seebeck coefficient α,
and the temperature difference, T1 – T2; VS = α (T1 – T2).
The junctions at T2 are commonly called the cold junction
because a common practice is to immerse the T2 junction
in 0°C ice/water slurry to make T2 independent of room
temperature variations. Thermocouple tables are based
on a cold-junction temperature of 0°C.
To date, IC manufacturers efforts to make microminiature
thermos bottles have not been totally successful. Therefore, an electronically simulated cold-junction is required
for most applications. The idea is basically to add a
temperature dependent voltage to VS such that the voltage
sum is the same as if the T2 junction were at a constant 0°C
instead of at room temperature. This voltage source is
called a cold junction compensator. Its output is designed
to be 0V at 0°C and have a slope equal to the Seebeck
coefficient over the expected range of T2 temperatures.
TEMPERATURE T1
TO BE MEASURED
Fe
Cu
T2
CONSTANTAN
}
VS
Cu
LT1025 MUST BE LOCATED
NEXT TO COLD JUNCTION
FOR TEMPERATURE TRACKING
LT1025 • AG01
Figure 1
To operate properly, a cold junction compensator must be
at exactly the same temperature as the cold junction of the
thermocouple (T2). Therefore, it is important to locate the
LT1025 physically close to the cold junction with local
temperature gradients minimized. If this is not possible,
1025fb
3
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. This resistor can be
connected to any convenient negative supply. It should be
selected to sink at least 30µA of current. Suggested value
for a – 5V supply is 150kΩ, and for a – 15V supply, 470kΩ.
Smaller resistors must be used if an external load is
connected to the 10mV/°C output. The LT1025 can source
up to 1mA of current, but there is a trade-off with internal
temperature rise.
Internal Temperature Rise
VOUT = αT + αß(T –25°)2
The LT1025 is specified for temperature accuracy assuming no internal temperature rise. At low supply voltages
this rise is usually negligible (≈ 0.05°C at 5V), but at higher
supply voltages or with external loads or pull-down current, internal rise could become significant. This effect can
be calculated from a simple thermal formula, ∆T = (θJA)
(V +)(IQ + IL), where θJA is thermal resistance from junction
to ambient, (≈130°C/W), V+ is the LT1025 supply voltage,
IQ is the LT1025 supply current (≈ 80µA) and IL is the total
load current including actual load to ground and any pulldown current needed to generate negative outputs. A
sample calculation with a 15V supply and 50µA pull-down
current would yield, (130°C/W) (15V) (80µA + 50µA) =
0.32°C. This is a significant rise in some applications. It
can be reduced by lowering supply voltage (a simple fix is
to insert a 10V zener in the VIN lead) or the system can be
calibrated and specified after an initial warm-up period of
several minutes.
ß ≈ 5.5 • 10– 4
Driving External Capacitance
LT1025 • AG02
Figure 2
The four thermocouple outputs on the LT1025 are
60.9µV/°C (E), 51.7µV/°C (J), 40.6µV/°C (K and T), and
6µV/°C (R and S). These particular coefficients are chosen
to match the room temperature (25°C) slope of the
thermocouples. Over wide temperature ranges, however,
the slope of thermocouples changes, yielding a quasiparabolic error compared to a constant slope. The LT1025
outputs have a deliberate parabolic “bow” to help
compensate for this effect. The outputs can be mathematically described as the sum of a linear term equal to room
temperature slope plus a quadratic term proportional to
temperature deviation from 25°C squared. The coefficient
(ß) of the quadratic term is a compromise value chosen to
offer improvement in all the outputs.
The actual ß term which would be required to best
compensate each thermocouple type in the temperature
range of 0°C to 50°C is: E, 6.6 • 10–4; J, 4.8 • 10–4;
K, 4.3 • 10–4; R, 1.9 • 10–3, S, 1.9 • 10–3; T, 1 • 10–3.
The temperature error specification for the LT1025
10mV/°C output (shown as a graph) assumes a ß of
5.5 •10 –4. For example, an LT1025 is considered “perfect”
if its 10mV/°C output fits the equation VO = 10mV(T) +
(10mV)(5.5 • 10 –4)(T – 25°C)2.
Operating at Negative Temperatures
The LT1025 is designed to operate with a single positive
supply. It therefore cannot deliver proper outputs for
The direct thermocouple drive pins on the LT1025 (J, K,
etc.) can be loaded with as much capacitance as desired,
but the 10mV/°C output should not be loaded with more
than 50pF unless external pull-down current is added, or
a compensation network is used.
Thermocouple Effects in Leads
Thermocouple voltages are generated whenever dissimilar materials are joined. This includes the leads of IC
packages, which may be kovar in TO-5 cans, alloy 42 or
copper in dual-in-line packages, and a variety of other
materials in plating finishes and solders. The net effect
of these thermocouples is “zero” if all are at exactly the
1025fb
4
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. If a gradient cannot be eliminated,
leads should be positioned isothermally, especially the
LT1025 R– and appropriate output pins, the amplifier input
pins, and the gain setting resistor leads. An effect to watch
for is amplifier offset voltage warm-up drift caused by
mismatched thermocouple materials in the wire-bond/
lead system of the IC package. This effect can be as high
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 and can occur in amplifiers with measured “zero”
drift. Warm-up drift is directly proportional to amplifier
power dissipation. It can be minimized by avoiding TO-5
cans, using low supply current amplifiers, and by using the
lowest possible supply voltages. Finally, it can be accommodated by calibrating and specifying the system after a
five minute warm-up period.
Reversing the Polarity of the 10mV/°C Output
The LT1025 can be made to “stand on its head” to achieve
a minus 10mV/°C output point. This is done as shown in
Figure 3. The normal output (VO) is grounded and feedback is established between the ground pin and the
positive supply pin by feeding both of them with currents
while coupling them with a 6V zener. The ground pin will
R2
15k
VIN
VO
LT1025
D1
VZ ≈ 6V
R1 =
V + – VZ (≈6 V)
V–
, R2 = –
300µA + IL
V /R1 + 280µA
For ±15V supplies, with IL = 20µA maximum, R1 = 47k and
R2 = 15k.
Amplifier Considerations
Thermocouple amplifiers need very low offset voltage and
drift, and fairly low bias current if an input filter is used. The
best precision bipolar amplifiers should be used for type
J, K, E, and T thermocouples which have Seebeck coefficients of 40µV/°C to 60µV/°C. In particularly critical applications or for R and S thermocouples (6µV/°C to 15µV/°C),
a chopper-stabilized amplifier is required. Linear Technology offers three amplifiers specifically tailored for thermocouple applications. The LTKA0x is a bipolar design with
extremely low offset (< 35µV), low drift (<1.5µV/°C), very
low bias current (<1nA), and almost negligible warm-up
drift (supply current is ≈ 400µA). It is very cost effective
even when compared with “jellybean” op amps with vastly
inferior specifications.
For the most demanding applications, the LTC1050 and
LTC1052 CMOS chopper-stabilized amplifiers offer 5µV
offset and 0.05µV/°C drift (even over the full military
temperature range). Input bias current is 30pA, and gain
is typically 30 million. These amplifiers should be used for
R and S thermocouples, especially if no offset adjustments can be tolerated, or a large ambient temperature
swing is expected.
V + (15V)
I+
now be forced by feedback to generate –10mV/°C as long
as the grounded output is supplying a net “source” current
into ground. This condition is satisfied by selecting R1
such that the current through R1 (I–) is more than the sum
of the LT1025 supply current, the maximum load current
(IL), and the minimum zener current (≈ 50µA). R2 is then
selected to supply more current than I–.
GND
VOUT
–10mV/°C
I–
R1
47k IL
V – (–15V)
Figure 3
RL
LT1025 • AG03
Regardless of amplifier type, it is suggested that for best
possible performance, dual-in-line (DIP) packages be
used to avoid thermocouple effects in the kovar leads of
TO-5 metal can packages if amplifier supply current exceeds 500µA. These leads can generate both DC and AC
offset terms in the presence of thermal gradients in the
package and/or external air motion.
1025fb
5
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. Thermocouple Nonlinearity, 0°C to 400°C
ERROR BEFORE OFFSETTING
VH
ERROR AFTER OFFSETTING
OUTPUT (V)
To avoid gain error, high open loop gain is necessary for
single-stage thermocouple amplifiers with 10mV/°C or higher
outputs. A type K amplifier, for instance, with 100mV/°C
output, needs a closed loop gain of ≈2,500. An ordinary op
amp with a minimum open loop of 50,000 would have an
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
accuracy. Minimum suggested open loop gain for type E, J,
K, and T thermocouples is 250,000. This gain is adequate for
type R and S if output scaling is 10mV/°C or less.
0
2.5
ERROR TYPE J AND K (°C)
In many situations, thermocouples are used in high noise
environments, and some sort of input filter is required.
(See discussion of input filters). To reject 60Hz pick-up
with reasonable capacitor values, input resistors in the
10k-100k range are needed. Under these conditions, bias
current for the amplifier needs to be less than 1nA to avoid
offset and drift effects.
OFFSET AMPLIFIER
SIMPLE AMPLIFIER
THERMOCOUPLE
VL
0
TL T1/6
TM
T5/6 TH
TEMPERATURE (°C)
LT1025 • G05
Thermocouple Nonlinearities
Thermocouples are linear over relatively limited temperature
spans if accuracies of better than 2°C are needed. The graph
in Figure 4 shows thermocouple nonlinearity for the
temperature range of 0°C to 400°C. Nonlinearities can be
dealt with in hardware by using offsets, breakpoints, or power
series generators. Software solutions include look-up tables,
power series expansions, and piece-wise approximations.
For tables and power series coefficients, the reader is referred
to the ASTM Publication 470A.
Hardware correction for nonlinearity can be as simple as an
offset term. This is shown in Figure 5. The thermocouple
shown in the figure has an increasing slope (α) with
Figure 5. Offset Curve Fitting
temperature. The temperature range of interest is between TL
and TH, with a calibration point at TM. If a simple amplifier is
used and calibrated at TM, the output will be very high at TL
and very low at TH. Adding the proper offset term and
calibrating at T1/6 or T5/6 can significantly reduce errors. The
technique is as follows:
1. Calculate amplifier gain:
G = (SF) (TH – TL)/(VH – VL)
SF = Output scale factor, e.g., 10mV/°C
VH = Thermocouple output at TH
VL = Thermocouple output at TL
2. Use precision resistors to set gain or calibrate gain by
introducing a precision “delta” input voltage and trimming
for proper “delta” output.
1025fb
6
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. The method which tends to
minimize worst-case error over the whole TL to TH range
Breakpoint correction for nonlinearity is more complicated than a simple offset, but a single breakpoint combined with offset will reduce errors typically by 4:1 over a
simple offset technique.
U
TYPICAL APPLICATIO S
Eliminating Amplifier Feedback Resistors
(Output Goes Negative with Increasing Temperature)
15V
VIN
LT1025
K
C1
0.1µF
GND
VO
R–
300k
–15V
2
–
–
3
+
VOUT
–10mV/°C
6
LTKA0x††
3k
+
15V
7
4
C2
1µF
–15V
TYPE K
†† OR EQUIVALENT. SEE “AMPLIFIER CONSIDERATIONS”
Type K Thermometer with Grounded Thermocouple
R3
255k
1%
R2
100Ω
R6
9.1k
V+
VIN
LT1025
V
+
GND
–
R5
10k
C2
1µF
LTKA0x††
VOUT
10mV/°C
VO
0.1µF
R1
1k
1%
R4*
470k
R–
V–
–15V
V–
IF OUTPUT MUST SINK CURRENT, R4
30µA
MUST BE DECREASED APPROPRIATELY. R4 IS NOT
REQUIRED (OPEN) FOR LT1025 TEMPERATURES ≥ 0°C
WHEN SOURCING CURRENT ONLY
††
OR EQUIVALENT. SEE “AMPLIFIER CONSIDERATIONS”
*R4 ≤
+
V–
TYPE K
1025fb
7
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 0.1µF
**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
VIN
LT1025 VO
6V
R1
1k
1%
GND
–10mV/°C
R4
141k
R5
47k
C1
0.1µF
–
–15V
–
R6
10k
+
1µF
R2
100Ω
15V
LTKA0x††
+
R3
141k
1% V
OUT
10mV/°C
0°C TO 500°C
–15V
TYPE E
*SEE “REVERSING THE POLARITY OF THE 10mV/°C OUTPUT”
††
OR EQUIVALENT. SEE “AMPLIFIER CONSIDERATIONS”
1025fb
8
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 = 9.998V AT T = 1000°C, OR FOR VIN AT +INPUT OF AMPLIFIER = 9.585mV
†
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
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
.045 – .065
(1.143 – 1.651)
.014 – .026
(0.360 – 0.660)
.100
(2.54)
BSC
.125
3.175
MIN
J8 0801
OBSOLETE PACKAGE
1025fb
10
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. DIMENSIONS ARE
INCHES
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)
NOTE 3
.045 ±.005
.050 BSC
8
.245
MIN
7
6
5
.160 ±.005
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
.030 ±.005
TYP
1
RECOMMENDED SOLDER PAD LAYOUT
.010 – .020
× 45°
(0.254 – 0.508)
.008 – .010
(0.203 – 0.254)
3
4
.053 – .069
(1.346 – 1.752)
.004 – .010
(0.101 – 0.254)
0°– 8° TYP
.016 – .050
(0.406 – 1.270)
NOTE:
1. DIMENSIONS IN
2
.014 – .019
(0.355 – 0.483)
TYP
INCHES
(MILLIMETERS)
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)
.050
(1.270)
BSC
SO8 0303
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
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. SEE “AMPLIFIER CONSIDERATIONS”
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1012
Picoamp Input Current Op Amp
120µV Max VOS, 280pA Max IOS
LTC1050
Zero Drift Amplifier
5µV Max VOS, AVOL 1V/µV Max
LTC2050
SOT-23 Zero Drift Amplifier
3µV Max VOS
1025fb
12 Linear Technology Corporation
LT/TP 1103 1K REV B • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
 LINEAR TECHNOLOGY CORPORATION 1988