Datasheet
TMP35/TMP36/TMP37 Data Sheet
Rev. H | Page 16 of 19
V
OUT
4
6
7
1µF
R5
100kΩ
V
OUT
R
L
250Ω
V
LOOP
9V TO 18V
3
2
D1: HP5082-2810
REF193
TMP3x
R7
100Ω
R3
1
R1
1
+V
S
R2
1
P2
1
4mA
ADJUST
D1
R4
1
R6
100kΩ
P1
1
20mA
ADJUST
GND
Q1
2N1711
0.1µF
2
4
6
3V
I
L
NOTE:
1
SEE TEXT FOR VALUES.
–
+
00337-032
+
OP193
Figure 33. Temperature to 4–20 mA Loop Transmitter
TEMPERATURE-TO-FREQUENCY CONVERTER
Another common method of transmitting analog information
from a remote location is to convert a voltage to an equivalent
value in the frequency domain. This is readily done with any of
the low cost, monolithic voltage-to-frequency converters (VFCs)
available. These VFCs feature a robust, open-collector output
transistor for easy interfacing to digital circuitry. The digital
signal produced by the VFC is less susceptible to contamination
from external noise sources and line voltage drops because the
only important information is the frequency of the digital sig-
nal. When the conversions between temperature and frequency
are done accurately, the temperature data from the sensors can
be reliably transmitted.
The circuit in Figure 34 illustrates a method by which the
outputs of these temperature sensors can be converted to a
frequency using the AD654. The output signal of the AD654 is
a square wave that is proportional to the dc input voltage across
Pin 4 and Pin 3. The transfer equation of the circuit is given by
)(10
TT
OFFSETTPM
OUT
CR
VV
f
TMP3x
+V
S
GND
6
4
2
3
7
8
5
1
AD654
V
OUT
10µF/0.1µF
5V
P2
100kΩ
R
OFF1
470Ω
f
OUT
OFFSET
R
OFF2
10Ω
R1
P1
R
T
1
0.1µF
C
T
1
5
V
R
PU
5kΩ
f
OUT
NB: ATT
A
(MIN),
f
OUT
= 0Hz
NOTE:
1
R
T
AND C
T
– SEE TABLE
SENSOR R
T
(R1 + P1) C
T
TMP35
TMP36
TMP37
11.8kΩ + 500Ω
16.2kΩ + 500Ω
18.2kΩ + 1kΩ
1.7nF
1.8nF
2.1nF
0
0337-031
Figure 34. Temperature-to-Frequency Converter
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