LT1025CS8#PBF Linear Technology, LT1025CS8#PBF Datasheet - Page 3

• Manufacturer Part Number: LT1025CS8#PBF
• Description: IC COMPENSATR THERM MCRPWR 8SOIC
• Manufacturer: Linear Technology
• Type: Thermocouple Conditionerr

Specifications of LT1025CS8#PBF

• Input Type: Voltage
• Output Type: Voltage
• Current - Supply: 150µA
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Interface: -

APPLICATIO S I FOR ATIO
TYPICAL PERFOR A CE CHARACTERISTICS
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, V
and the temperature difference, T1 – T2; V
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.
–10
–2
–4
–6
–8
10
8
6
4
2
0
*ERROR CURVE FACTORS IN THE NONLINEARITY
–50
10mV/ C Output Temperature
Error LT1025
TERM BUILT IN TO THE LT1025. SEE THEORY OF
OPERATION IN APPLICATION GUIDE SECTION
–25
S
JUNCTION TEMPERATURE ( C)
, is the product of the Seebeck coefficient ,
GUARANTEED LIMITS*
0
LT1025
25
U
50
U
75
W
100
LT1025 • G01
U
125
W
S
=
–1
–2
–3
–4
–5
5
4
3
2
1
0
*ERROR CURVE FACTORS IN THE NONLINEARITY
–50
10mV/ C Output Temperature
Error LT1025A
TERM BUILT IN TO THE LT1025. SEE THEORY OF
OPERATION IN APPLICATION GUIDE SECTION
U
(T1 – T2).
–25
JUNCTION TEMPERATURE ( C)
GUARANTEED LIMITS*
0
LT1025A
25
To date, IC manufacturers efforts to make microminiature
thermos bottles have not been totally successful. There-
fore, an electronically simulated cold-junction is required
for most applications. The idea is basically to add a
temperature dependent voltage to V
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.
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,
50
TO BE MEASURED
TEMPERATURE
75
100
LT1025 • G02
125
T1
CONSTANTAN
120
200
180
160
140
100
Fe
80
60
40
20
0
Figure 1
Supply Current
0
DOES NOT INCLUDE 30 A
PULL-DOWN CURRENT
REQUIRED FOR TEMPERATURES
BELOW 0 C
5
T2
10
SUPPLY VOLTAGE (V)
S
Cu
Cu
LT1025 MUST BE LOCATED
NEXT TO COLD JUNCTION
FOR TEMPERATURE TRACKING
T
T
T
J
J
15
such that the voltage
J
= 125 C
= –55 C
= 25 C
}
V
20
S
PIN 4 TIED TO PIN 5
LT1025
25
30
LT1025 • AG01
LT1025 • G03
35
1025fb
3
40