VCC1

VCC2

GND1

GND2

16

14

12

2, 8

9, 15

P3.1

P3.0

UCA0TXD

UCA0RXD

11

15

16

12

4

XOUT

XIN

5

6

2

MSP430F2132

INA

OUTD

1

3

5

4

6

ISO7842

DVss

DVcc

0.1 F

0.1 F

0.1 F

EN1

EN2

7

10

INB

13

11

OUTB

INC

IND

16

0.1 F

OUTC

Vcc

GND

15

T1IN

9

11

12

10

C2–

3

R1OUT

T2IN

14

13

5

7

8

VS–

6

4

2

1

R2OUT

VS+

C1+

C1–

C2+

TRS232

4.7k

4.7k

R1IN

T1OUT

R2IN

T2OUT

1 F

1 F

1 F

1 F

TxD

RxD

RST

CST

ISOGND

10 F

0.1 F

MBR0520L

MBR0520L

1:2.1

0.1 F

3

1

D2

SN6501

D1

Vcc

4, 5

2

GND

3.3V

IN

ON

GND

OU

T

1

5

4

3

LP2985-50

3.3 F

10 F

Isolation

Barrier

VIN

5VISO

2

BP

10nF

OUTA

Figure 8-1. Isolated RS-232 Interface

8.2.1 Design Requirements

For this design example, use the parameters shown in Table 8-1.

Table 8-1. Design Parameters

PARAMETER

VALUE

Supply voltage

2.25V to 5.5V

Decoupling capacitor between VCC1 and GND1

0.1µF

Decoupling capacitor from VCC2 and GND2

0.1µF

8.2.2 Detailed Design Procedure

Unlike optocouplers, which require external components to improve performance, provide bias, or limit current,

the ISO7842 device only requires two external bypass capacitors to operate.

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ISO7842, ISO7842F

SLLSEJ0I – OCTOBER 2014 – REVISED JULY 2025

Copyright © 2025 Texas Instruments Incorporated

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