TMP01FSZ1 datasheet(13/20 Pages) AD

13 / 20 page

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 μA 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 μF. 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

HYSTERESIS

GENERATOR

WINDOW

COMPARATOR

TMP01

OP177

VPTAT

VOUT

V+

V–

V+

100

Ω

10k

Ω

0.1µF

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 μA maximum, and the OP90s is 20 μA 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

HYSTERESIS

GENERATOR

WINDOW

COMPARATOR

TMP01

1/2

OP297

1/2

OP297

AMP03

VPTAT

VOUT

V+

Ω

10k

Ω

10k

Ω

V–

V+

10k

Ω

Figure 26. Send the Signal Differentially for Noise Immunity

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