8 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, as well as validating and testing their design

implementation to confirm system functionality.

8.1 Application Information

The ISO7821 is a high-performance, dual-channel digital isolator with 5.7 kVRMS isolation voltage per UL 1577.

The device uses single-ended CMOS-logic switching technology. The supply voltage range is from 2.25 V to

5.5 V for both supplies, VCC1 and VCC2. Keep in mind that when designing with digital isolators, 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.

8.2 Typical Application

ISO782 1 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 .

VCC1

VCC2

GND1

GND2

INA

14

13

12

1, 7

9, 16

4

XOUT

XIN

5

6

2

MSP430G2132

OUTA

3

4

5

ISO7821

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

Isolation 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 × 2.2 nF

5

4

20

0.1 F

22

0.1 F

1 F

LOOP±

LOOP+

1

Figure 8-1. Isolated 4-20 mA Current Loop

8.2.1 Design Requirements

For the ISO7821, use the parameters shown in Table 8-1.

Table 8-1. Design Parameters

PARAMETER

VALUE

Supply voltage

2.25 V to 5.5 V

Decoupling capacitor between VCC1 and GND1

0.1 µF

Decoupling capacitor from VCC2 and GND2

0.1 µF

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ISO7821, ISO7821F

SLLSEM2H – NOVEMBER 2014 – REVISED NOVEMBER 2024

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Product Folder Links: ISO7821 ISO7821F