Datasheet

TMP01
Rev. E | Page 13 of 20
BUFFERING THE TEMPERATURE OUTPUT PIN
The VPTAT sensor output is a low impedance dc output voltage
with a 5 mV/K temperature coefficient, that is useful in multiple
measurement and control applications. In many applications,
this voltage needs to be transmitted to a central location for
processing. The buffered VPTAT voltage output is capable of
500 A drive into 50 pF (maximum).
Consider external amplifiers for interfacing VPTAT to external
circuitry to ensure accuracy, and to minimize loading which
could create dissipation-induced temperature sensing errors.
An excellent general-purpose buffer circuit using the OP177 is
shown in Figure 25. It is capable of driving over 10 mA, and
remains stable under capacitive loads of up to 0.1 F. Other
interfacing ideas are also provided in this section.
DIFFERENTIAL TRANSMITTER
In noisy industrial environments, it is difficult to send an
accurate analog signal over a significant distance. However,
by sending the signal differentially on a wire pair, these errors
can be significantly reduced. Because the noise is picked up
equally on both wires, a receiver with high common-mode
input rejection can be used to cancel out the noise very effec-
tively at the receiving end. Figure 26 shows two amplifiers used
to send the signal differentially, and an excellent differential
receiver, the AMP03, which features a common-mode rejection
ratio of 95 dB at dc and very low input and drift errors.
TEMPERATURE
SENSOR AND
VOLTAGE
REFERENCE
VREF
VPTAT
1
2
3
4
8
7
6
5
HYSTERESIS
GENERATOR
WINDOW
COMPARATOR
TMP01
OP177
R1
R2
R3
VPTAT
V
OUT
C
L
V
+
V–
V+
100Ω
10kΩ
0.1µF
0
0333-025
Figure 25. Buffer VPTAT to Handle Difficult Loads
4 mA TO 20 mA CURRENT LOOP
Another common method of transmitting a signal over long
distances is to use a 4 mA to 20 mA loop, as shown in Figure 27.
An advantage of using a 4 mA to 20 mA loop is that the
accuracy of a current loop is not compromised by voltage drops
across the line. One requirement of 4 mA to 20 mA circuits is
that the remote end must receive all of its power from the loop,
meaning that the circuit must consume less than 4 mA.
Operating from 5 V, the quiescent current of the TMP01 is
500 A maximum, and the OP90s is 20 A maximum, totaling
less than 4 mA. Although not shown, the open collector outputs
and temperature setting pins can be connected to do any local
control of switching.
TEMPERATURE
SENSOR AND
VOLTAGE
REFERENCE
VREF
VPTAT
1
2
3
4
8
7
6
5
HYSTERESIS
GENERATOR
WINDOW
COMPARATOR
TMP01
1/2
OP297
1/2
OP297
AMP03
R1
R2
R3
VPTAT
V
OUT
V
+
50Ω
10kΩ
10kΩ
50Ω
V–
V+
10kΩ
00333-026
Figure 26. Send the Signal Differentially for Noise Immunity