TMP17FS Analog Devices Inc, TMP17FS Datasheet - Page 7

• Manufacturer Part Number: TMP17FS
• Description: IC TRANSDUC TEMP CUR OUT 8SOIC
• Manufacturer: Analog Devices Inc

Specifications of TMP17FS

• Rohs Status: RoHS non-compliant
• Sensing Temperature: -40°C ~ 105°C
• Output Type: Current
• Voltage - Supply: 4 V ~ 30 V
• Accuracy: ±2.5°C
• Package / Case: 8-SOIC (0.154", 3.90mm Width)

R
by the potentiometer R
temperature range –25 C to +105 C. The reference maintains a
constant set point voltage and ensures that approximately 7 V
appear across the sensor. If it is necessary to guardband for
extraneous noise, hysteresis can be added by tying a resistor
from the output to the ungrounded end of R
Multiple remote temperatures can be measured using several
TMP17s with a CMOS multiplexer or a series of 5 V logic gates
because of the device’s current-mode output and supply-voltage
compliance range. The on resistance of a FET switch or output
impedance of a gate will not affect the accuracy, as long as 4 V
is maintained across the transducer. Muxes and logic driving
circuits should be chosen to minimize leakage current related
errors. Figure 13 illustrates a locally controlled mux switching
the signal current from several remote TMP17s. CMOS or TTL
gates can also be used to switch the TMP17 supply voltages,
with the multiplexed signal being transmitted over a single twisted
pair to the load.
To minimize the number of muxes required when a large number
of TMP17s are being used, the circuit can be configured in a
matrix. That is, a decoder can be used to switch the supply voltage
to a column of TMP17s while a mux is used to control which
row of sensors is being measured. The maximum number of
TMP17s that can be used is the product of the number of channels
of the decoder and mux.
An example circuit controlling 80 TMP17s is shown in Figure 14.
A 7-bit digital word is all that is required to select one of the
sensors. The enable input of the multiplexer turns all the sensors
off for minimum dissipation while idling.
REV. A
HIGH
T
8
+
–
and R
Figure 13. Remote Temperature Multiplexing
T
2
+
–
LOW
T
1
+
–
determine the limits of temperature controlled
REMOTE
TMP17s
SET
. The circuit shown operates over the
S1
S2
S8
AD7501
+15V
TTL DTL TO
CMOS I/O
E
N
CHANNEL
SELECT
–15V
LOW.
10k
V
OUT
–7–
To convert the TMP17 output to °C or °F, a single inexpensive
reference and op amp can be used as shown in Figure 15. Although
this circuit is similar to the two temperature trim circuit shown
in Figure 5, there are two important differences. First, the gain
resistor is fixed, alleviating the need for an elevated temperature
trim. Acceptable accuracy can be achieved by choosing an inex-
pensive resistor with the correct tolerance. Second, the TMP17
calibration error can be trimmed out at a known convenient
temperature (e.g., room temperature) with a single potentiometer
adjustment. This step is independent of the gain selection.
+15V
REF43
Figure 15. Celsius or Fahrenheit Thermometer
+5V
2.5V
4028 BCD TO DECIMAL DECODER
R
OFFSET
Figure 14. Matrix Multiplexer
R
R
OFFSET
/R
GAIN
COLUMN
R
SELECT
80–TMP17s
CAL
+
–
V–
TMP17
OP196
R
GAIN
V
OUT
= 100mV/( C OR F)
C
F
+
–
R
OFFSET
9 .1 k
9.8k
TMP17
SELECT
ROW
100k
180k
E
R
N
GAIN
+15V
–15V
V
10k
OUT