TMP01

REV. C

–12–

Buffering the Temperature Output Pin

The VPTAT sensor output is a low impedance dc output volt-

age with a 5 mV/K temperature coefficient, and is useful in a

number of measurement and control applications. In many ap-

plications, this voltage needs to be transmitted to a central loca-

tion for processing. The buffered VPTAT voltage output is

capable of 500

µA drive into 50 pF (max). As mentioned in the

discussion above regarding buffering circuits for the VREF out-

put, it is useful to consider external amplifiers for interfacing

VPTAT to external circuitry to ensure accuracy, and to mini-

mize loading which could create dissipation-induced tempera-

ture sensing errors. An excellent general-purpose buffer circuit

using the OP177 is shown in Figure 17 which is capable of driv-

ing over 10 mA, and will remain stable under capacitive loads of

up to 0.1

µF. Other interfacing ideas are shown below.

Differential Transmitter

In noisy industrial environments, it is difficult to send an accu-

rate analog signal over a significant distance. However, by send-

ing the signal differentially on a wire pair, these errors can be

significantly reduced. Since the noise will be picked up equally

on both wires, a receiver with high common-mode input rejec-

tion can be used to cancel out the noise very effectively at the

Figure 17. Buffer VPTAT to Handle Difficult Loads

receiving end. Figure 18 shows two amplifiers being 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.

0.1

µF

V+

V–

C

L

V

OUT

VPTAT

OP177

V+

R1

R2

R3

100

Ω

TEMPERATURE

SENSOR &

VOLTAGE

REFERENCE

1

2

3

4

HYSTERESIS

GENERATOR

WINDOW

COMPARATOR

TMP01

VPTAT

VREF

7

8

5

6

10k

Ω

V

OUT

VPTAT

1/2

OP297

V+

R1

R2

R3

50

Ω

TEMPERATURE

SENSOR &

VOLTAGE

REFERENCE

1

2

3

4

HYSTERESIS

GENERATOR

WINDOW

COMPARATOR

TMP01

VPTAT

VREF

7

8

5

6

10k

Ω

V+

V–

10k

Ω

1/2

OP297

10k

Ω

AMP03

50

Ω

Figure 18. Send the Signal Differentially for Noise Immunity