VCC1

VCC2

GND1

GND2

INA

8

7

6

4

5

4

XOUT

XIN

5

6

2

MSP430

G2132

OUTA

1

2

3

ISO7421

DVSS

DVCC

INB

OUTB

P3.0

P3.1

11

12

10 F

VS

0.1 F

MBR0520L

MBR0520L

1:1.33

0.1 F

3

1

D2

SN6501

D1

VCC

4, 5

2

GND

3.3 V

IN

EN

GND

OUT

1

5

2

3

TPS76333

10 F

3.3VISO

10 F

ISO-BARRIER

0.1 F

0.1 F

0.1 F

0.1 F

3

VD

COMA

BASE

LOW

10

8

ERRLVL

DBACK

16

DIN

DAC161P997

OUT

9

C1

14

15

VA

COMD

2

C2

13

C3

12

3 × 22 nF

5

4

20

0.1 F

22

0.1 F

1 F

LOOP±

LOOP+

1

ISO7421-EP

SLLSEN3 – DECEMBER 2015

www.ti.com

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

The ISO7421-EP device uses a single-ended TTL-logic switching technology. Its supply voltage range is from

3.15 V to 5.25 V for both supplies, VCC1 and VCC2. When designing with digital isolators, it is important to keep in

mind that due to the single-ended design structure, digital isolators do not conform to any specific interface

standard and are only intended for isolating single-ended CMOS or TTL digital signal lines. The isolator is

typically placed between the data controller (that is,

μC or UART), and a data converter or a line transceiver,

regardless of the interface type or standard.

9.2 Typical Application

ISO7421-EP can be used with Texas Instruments' mixed signal micro-controller, digital-to-analog converter,

transformer driver, and voltage regulator to create an isolated 4-20 mA current loop.

Figure 12. Isolated 4- to 20-mA Current Loop

9.2.1 Design Requirements

For applications that require isolation in place of using x-fmr to provide isolation, ISO7421-EP meets the system

needs with small size. Unlike optocouplers, which require external components to improve performance, provide

bias, or limit current, the ISO7421-EP device only requires two external bypass capacitors to operate.

14

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