LTK001
Thermocouple Cold Junction
Compensator and
Matched Amplifier
FEATURES
■
■
■
■
■
■
0.75°C Initial Accuracy (A Version)
Extremely Low Warmup Drift
Preset Outputs for Type E, J, K, R, S, T
Single 5V to
±
20V Operation
480µA Typical Supply Current
Available in 8-Pin DIP Package
thermocouple applications. It has low supply current to
minimize warmup drift, very low offset voltage (<35µV),
high gain, and extremely low input bias currents (<600pA)
to allow high impedance input filters to be used without
degrading offset voltage or drift.
Matching of the kits is accomplished by separating the
compensators and amplifiers according to the polarity of
their initial (room temperature) errors. This eliminates the
need to sum the errors of the two components to find the
worst-case error.
The LTK001 has direct thermocouple outputs of
60.9µV/°C (E), 51.7µV/°C (J), 40.6µV/°C (K, T), and
5.95µV/°C (R, S). It also has a 10mV/°C output which can
be scaled to match any arbitrary thermocouple.
For multiple thermocouple applications using one com-
pensator, amplifiers may be ordered separately (LTKA0x),
still matched to the compensator.
, LTC and LT are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. For typical performance curves and
applications circuits consult the LT1025 data sheet.
APPLICATIO S
■
Thermocouple Cold Junction Compensation
DESCRIPTIO
The LTK001 is a thermocouple amplifier supplied with a
matched cold junction compensator. By separating the
amplifier and compensator functions, the problem of
compensator temperature rise is virtually eliminated. The
compensator is a selected version of the LT
®
1025 cold
junction compensator. The amplifier, which is also avail-
able separately as LTKA0x has been specially selected for
TYPICAL APPLICATIO
V+
V
IN
LT1025
GND
U
U
R2
100Ω
FULL-SCALE TRIM
R1
1k
1%
U
Type K 10mV/°C Thermometer
R3**
255k
1%
C2
0.1µF
V+
–
LTKA0x
K
–
*
+
C1
0.1µF
+
V–
V
OUT
10mV/°C
V
0
R–
TYPE K
R4*
–
*R4
≤
V , R4 IS NOT REQUIRED (OPEN) FOR
30µA
LT1025 TEMPERATURES
≥
0°C.
**SELECTED FOR 0°C–100°C RANGE
LTK001 TA01
V–
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1
LTK001
ABSOLUTE
AXI U
RATI GS
Amplifier (LTKA0x)
Supply Voltage (Total V
+
to V
–
) ............................... 40V
Differential Input Current (Note 2) ......................
±10mA
Common Mode Input Voltage ............. Equal to Supplies
Output Short-Circuit Duration .......................... Indefinite
Compensator (LT1025)
Supply Voltage (V
IN
to Ground Pin) ......................... 36V
Output Voltage (Forced) ............................................ 5V
Output Short-Circuit Duration .......................... Indefinite
PACKAGE/ORDER I FOR ATIO
TOP VIEW
E
60.9µV/°C 1
V
IN
2
V
O
10mV/°C 3
GND 4
N8 PACKAGE
8-LEAD PDIP
COMPENSATOR
(LT1025)
T
JMAX
= 100°C,
θ
JA
= 130°C/W (N8)
8
7
6
5
J
51.7µV/°C
K,T
40.6µV/°C
R,S
6µV/°C
R–
COMMON
V
OS
TRIM 1
–IN 2
+IN 3
V– 4
N8 PACKAGE
8-LEAD PDIP AMPLIFIER
(LTKA0x)
T
JMAX
= 100°C,
θ
JA
= 130°C/W
ORDER PART NUMBER
KIT
LTK001CN8
LTK001ACN8
J8 PACKAGE
8-LEAD CERDIP
COMPENSATOR
(LT1025)
T
JMAX
= 150°C,
θ
JA
= 100°C/W (J8)
ORDER PART NUMBER
AMPLIFIER ONLY
(Note A)
LTKA00CN8
LTKA01CN8
LTK001MJ8
LTK001AMJ8
OBSOLETE PACKAGE
Consider the N8 Package for Alternate Source
Note A:
The polarity of the amplifier is indicated by the 0 or 1 in the part
number. An LT1025 with a 0 identifier is properly matched with an LTKA00,
while an LT1025 with a 1 identifier should be used with an LTKA01.
Consult factory for parts specified with wider operating temperature ranges.
2
U
U
W
W W
U
W
(Note 1)
Both Devices
Operating Temperature Range
LTK001AMJ8, LTK001MJ8
(OBSOLETE)
......................................................... – 55°C to 125°C
LTK001ACN8, LTK001CN8 ...................... 0°C to 70°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature Range (Soldering, 10 sec.)...... 300°C
TOP VIEW
8
7
6
5
V
OS
TRIM
V+
OUT
OVER COMP
+IN 3
V
OS
TRIM 1
–IN 2
TOP VIEW
V
OS
TRIM
8
–
+
7 V
+
6 OUT
5 OVER COMP
4
V
–
H PACKAGE
8-LEAD TO-5 METAL CAN
AMPLIFIER (LTKA0x)
T
JMAX
= 150°C,
θ
JA
= 150°C/W,
θ
JC
= 45°C/W
ORDER PART NUMBER
AMPLIFIER ONLY
(Note A)
LTKA00MH
LTKA01MH
OBSOLETE PACKAGE
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LTK001
ELECTRICAL CHARACTERISTICS
(Matched Amplifier and Compensator)
T
A
= 25°C, V
S
=
±15V
(Amplifier), V
S
= 5V (Compensator)
PARAMETER
Total Temperature Error at 25°C
(Note 3)
CONDITIONS
Type E
Type J
Type K, T
Type R, S
Slope Error (Notes 4 and 9)
0°C
≤
T
J
≤
70°C
Type E
Type J
Type K, T
Type R, S
Total Temperature Error at
Temperature Extremes (Note 9)
0°C
≤
T
J
≤
70°C
Type E
Type J
Type K, T
Type R, S
– 55°C
≤
T
J
≤
125°C
Type E
Type J
Type K, T
Type R, S
Temperature Error Change with
Supply Voltage (Note 5)
Supply Current
480
(Note 12)
(Note 12)
(Note 12)
MIN
LTK001A
TYP
MAX
0.75
0.75
0.86
5.0
0.05
0.06
0.07
0.28
2.0
2.1
2.6
16
6
6
6.3
30
0.1
900
480
MIN
LTK001
TYP
MAX
2.5
2.5
2.5
5.0
0.09
0.09
0.10
0.32
5
5
5.2
16
8.5
8.5
9
30
0.1
900
UNITS
°C
°C
°C
°C
°C/°C
°C/°C
°C/°C
°C/°C
°C
°C
°C
°C
°C
°C
°C
°C
°C/V
µA
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LTK001
ELECTRICAL CHARACTERISTICS
(Compensator LT1025)
The
●
denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
S
= 5V unless otherwise noted.
PARAMETER
Temperature Error at 10mV/°C Output (Note 9)
CONDITIONS
T
J
= 25°C, LTK001A
T
J
= 25°C, LTK001
Full Temperature Span
Temperature Error at Individual Outputs (Note 10)
LTK001A: E, J, K, T
LTK001A: R, S
LTK001: E, J, K, T
LTK001: R, S
Full Temperature Span
Supply Current
4V
≤
V
IN
≤
36V
0°C
≤
T
J
≤
70°C
– 55°C
≤
T
J
≤
125°C
Change in Supply Current
Line Regulation (Note 11)
Load Regulation (Note 11)
Divider Impedance
4V
≤
V
IN
≤
36V
4V
≤
V
IN
≤
36V
10mV/°C Output
0
≤
I
O
≤
1mA
10mV/°C Output
E
J
K, T
R, S
●
●
●
●
●
●
COMPENSATOR (LT1025)
MIN
TYP
MAX
0.3
0.5
0.4
0.4
0.8
1.2
80
0.5
2.0
0.75
1.5
2.4
3.5
100
150
200
0.01
0.003
0.04
2.5
2.1
4.4
3.8
0.05
0.02
0.2
UNITS
°C
°C
°C
°C
°C
°C
µA
µA
µA
µA/V
°C/V
°C
kΩ
kΩ
kΩ
kΩ
See Curve on LT1025 Data Sheet
See Curve on LT1025 Data Sheet
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LTK001
ELECTRICAL CHARACTERISTICS
(Amplifier LTKA0x)
The
●
denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
S
=
±15V,
V
CM
= 0V, T
J
= 25°C unless otherwise noted.
PARAMETER
Input Offset Voltage
Input 0ffset Voltage Drift with Temperature
Input Bias Current
Input Bias Current Drift with Temperature
lnput 0ffset Current
lnput Offset Current Drift with Temperature
Large Signal Voltage Gain
Common Mode Rejection Ratio
Power Supply Rejection Ratio
Common Mode Input Voltage Range
Output Voltage Swing (Notes 6, 8)
Supply Current
Supply Voltage Range
Total V
+
to V
–
Voltage
(Note 6)
0°C
≤
T
A
≤
70°C
– 55°C
≤
T
A
≤
125°C
(Note 6)
0°C
≤
T
A
≤
70°C
– 55°C
≤
T
A
≤
125°C
(Note 6)
R
L
= 10kΩ
V
CM
=
±
13.5V
±
2.5V
≤
V
S
≤
±
20V (Note 5)
Notes 6, 7
Referred to Supplies
Above V
–
Below V
+
I
OUT
= 0.1mA
I
OUT
= 1mA
●
●
●
●
●
●
●
●
●
●
●
CONDITIONS
AMPLIFIER (LTKA0x)
MIN
TYP
MAX
10
0.3
±
200
±
300
1
±
100
±
200
0.6
400
106
106
0.75
1.0
0.8
1.1
400
4.5
800
40
2000
130
125
35
1.5
±
600
±
1500
5
±
500
±
700
4
UNITS
µV
µV/°C
pA
pA
pA/°C
pA
pA
pA/°C
V/mV
dB
dB
V
V
V
V
µA
V
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The inputs of the LTKA0x amplifier are clamped with diodes, so a
differential voltage rating does not apply.
Note 3:
Total temperature error is the overall error at 25°C taking into
account the offset of the amplifier, the offset at the compensator 10mV/°C
output, and the error in the compensator divider network. Warmup drift is
not included.
Note 4:
Slope error is the increase in total temperature error as ambient
temperature is increased. It is guaranteed by design and by other tests,
but is not tested directly.
Note 5:
This is a worst-case limit assuming that any or all supply voltages
change.
Note 6:
Guaranteed, but not tested.
Note 7:
By referring common mode range to the supplies, the range
referred to ground can be quickly calculated for any given supply voltage.
With a single 5V supply, for instance, which has a worst-case low value of
4.7V, the upper common mode limit is 4.7V – 1V = 3.7V. The lower
common mode limit is 0V + 0.75V = 0.75V. With
±15V
supplies, the limits
would be 14V and –14.25V, respectively. Common mode range has a
temperature sensitivity of
≈
2mV/°C.
Note 8:
Absolute output voltage swing is calculated by subtracting the
given limits from actual supply voltage. These limits indicate the point
where offset voltage has changed suddenly by 5µV.
Note 9:
Temperature error is defined as the deviation from the following
formula:
V
OUT
=
α(T)
+
α
ß(T
– 25°C)
2
α
= Typical thermocouple Seebeck coefficient as follows,
E = 60.9µV/°C, J = 51.7µV/°C, K, T = 40.6µV/°C, R, S = 5.95µV/°C.
α
= 10mV/°C at the 10mV output.
ß
= Nonlinearity coefficient built into the LT1025 to help compensate
for the nonlinearities of thermocouples.
ß
= 5.5 x 10
–4
, generating
0.34°C bow for 25°C temperature change, and 1.36°C bow for 50°C
change.
Note 10:
Temperature error at the individual outputs is the sum of the
10mV/°C output error plus the resistor divider error.
Note 11:
Line and load regulation do not take into account the effects of
self-heating. Output changes due to self-heating can be calculated as
follows:
∆V
OUT
(Line) =
∆V
IN
(I
q
+ I
load
)(150°C/W)
∆V
OUT
(Load) = (∆I
load)
(V
IN
)(150°C/W)
= LT1025 supply current
Load regulation is 30µA
≤
I
O
≤
1mA for T
A
≤
0°C.
Note 12:
Larger errors with type R and S thermocouples are due mostly to
35µV offset of the amplifier. This error can be reduced to 5µV max with the
LTC
®
1050 or LTC1052 operational amplifiers.
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Embedded System
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