R

1

R

2

R

4

INA105

Difference Amp

R

3

R

S

2

3

4

IN4689

5.1V

Reference

5

7

6

1

V

IN

Signal Source

+

10kΩ

15

–V

S2 (–15V)

+V

S2 (+15V)

V

S1 (+15V)

16

–V

S1

Com 2

10

In

Gnd

RC

(1)

V

S

(V)

20+

15

12

INPUT RANGE

(V)(1)

–2 to +10

–2 to +5

–2 to +2

7

9

8

ISO124

2

1

V

OUT = VIN

R

CM

1kΩ

RCV420

XTR105

R

G

R

Z

(1)

13

3

4

2

6

7

10

14

1

0.01µF

4-20mA

RTD

(PT100)

0.8mA

0.8mA

1.6mA

14

15

16

3

2

10

4

12

11

5, 13

15

16

2

1

Gnd

–V

S = –15V

on PWS740

+V

S = 15V on PWS740

9

10

7

8

–V

+V

ISO124

V

OUT

0V - 5V

16

ISO124

SBOS074E – SEPTEMBER 1997 – REVISED JUNE 2018

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Copyright © 1997–2018, Texas Instruments Incorporated

Typical Applications (continued)

8.2.5 Isolated 4-mA to 20-mA Instrument Loop

For isolated temperature measurements in a 4-mA to 20-mA loop, Figure 20 provides a solution using the

XTR101 and RCV420 devices. A high-performance PT100 resistance temperature detector (RTD) provides the

user with an isolated 0-V to 5-V representation of the isolated temperature measurement.

Figure 20. Isolated 4- to 20-mA Instrument Loop (RTD Shown)

8.2.6 Single-Supply Operation of the ISO124 Isolation Amplifier

The circuit shown in Figure 21 uses a 5.1-V Zener diode to generate the negative supply for an ISO12x from a

single supply on the high-voltage side of the isolation amplifier. The input measuring range will be dependent on

the applied voltage as noted in the accompanying table.

NOTE: Because the amplifier is unity gain, the input range is also the output range. The output can go to –2 V because the

output section of the ISO amp operates from dual supplies.

For additional information see Single-Supply Operation of Isolation Amplifiers.

Figure 21. Single-Supply Operation of the ISO124 Isolation Amplifier Schematic