TMP17GS Analog Devices Inc, TMP17GS Datasheet - Page 6

• Manufacturer Part Number: TMP17GS
• Description: IC TRANSDUC TEMP CUR OUT 8SOIC
• Manufacturer: Analog Devices Inc

Specifications of TMP17GS

• Rohs Status: RoHS non-compliant
• Sensing Temperature: -40°C ~ 105°C
• Output Type: Current
• Voltage - Supply: 4 V ~ 30 V
• Accuracy: ±3.5°C
• Package / Case: 8-SOIC (0.154", 3.90mm Width)

TMP17
The circuit in Figure 8 demonstrates a method in which a voltage
output can be derived in a differential temperature measurement.
R1 can be used to trim out the inherent offset between the two
devices. By increasing the gain resistor (10 kΩ), temperature mea-
surements can be made with higher resolution. If the magnitude
of V1 and V2 is not the same, the difference in power consumption
between the two devices can cause a differential self-heating error.
Cold junction compensation (CJC) used in thermocouple signal
conditioning can be implemented using a TMP17 in the circuit
configuration of Figure 9. Expensive simulated ice baths or hard
to trim, inaccurate bridge circuits are no longer required.
The circuit shown can be optimized for any ambient temperature
range or thermocouple type by simply selecting the correct value
for the scaling resistor R. The TMP17 output (1 µA/K)
should approximate the line best fit to the thermocouple curve
(slope in V/ C) over the most likely ambient temperature range.
Additionally, the output sensitivity can be chosen by selecting
the resistors R
offset adjustment shown simply references the TMP17 to C. Note
that the TC of the reference and the resistors are the primary
contributors to error. Temperature rejection of 40 to 1 can be
easily achieved using the above technique.
Although the TMP17 offers a noise immune current output, it
is not compatible with process control/industrial automation
current loop standards. Figure 10 is an example of a temperature
to 4–20 mA transmitter for use with 40 V, 1 kΩ systems.
MEASURING
JUNCTION
Figure 9. Thermocouple Cold Junction Compensation
+
–
+
–
TMP17
TMP17
Figure 8. Differential Measurements
Cu
R
+
–
G1
50k
Cu
TMP17
REFERENCE
and R
R1
JUNCTION
–V
+V
5M
G2
REF43
10k
for the desired noninverting gain. The
1k
+7.5V
100k
OP196
10k
10k
2.5V
V
OUT
(1k )
R
THERMOCOUPLE
TYPE
J
K
T
E
S
R
G2
= (T
+
1
–
– T
OP193
2
)
R
G1
(10mV/ C)
APPROX.
R VALUE
52
41
41
61
6
6
R
V
OUT
–6–
In this circuit the 1 µA/K output of the TMP17 is amplified to
1 mA/°C and offset so that 4 mA is equivalent to 17°C and 20 mA
is equivalent to 33°C. R
intermediate reference temperature. With a suitable choice of
resistors, any temperature range within the operating limits of
the TMP17 may be chosen.
Reading temperature with a TMP17 in a microprocessor based
system can be implemented with the circuit shown in Figure 11.
By using a differential input A/D converter and choosing the current
to voltage conversion resistor correctly, any range of temperatures
(up to the 145 C span the TMP17 is rated for) centered at any
point can be measured using a minimal number of components.
In this configuration, the system will resolve up to 1 C.
A variable temperature controlling thermostat can easily be built
using the TMP17 in the circuit in Figure 12.
TMP17
Figure 10. Temperature to 4 –20 mA Current Transmitter
TMP17
REF43
REF01E
10k
+
–
Figure 12. Variable Temperature Thermostat
+
–
+5V
Figure 11. Temperature to Digital Output
10V
+
–
2.5V
R
10mV/ C
OFFSET
C
C
+15V
R
R
OFFSET
/R
GAIN
REF01E
35.7k
62.7k
R
27.3k
10k
R
T
CAL
10k
R
R
5k
HIGH
LOW
is trimmed for proper reading at an
SET
R
+
–
T
V–
12.7k
10
TMP17
OP196
COMPARATOR
R
GAIN
OP97
AD790
R
17 C
33 C
V
HYST
OUT
C
= 100mV/( C OR F)
4mA
20mA
5k
(OPTIONAL)
C
F
+
–
R
R
PULL-UP
500
TEMP > SETPOINT
OUTPUT HIGH
TEMP < SETPOINT
OUTPUT LOW
OFFSET
9 .1 k
9.8k
1mA/ C
+
V
T
100k
180k
R
GAIN
–
REV. A
+20V
–20V