8.2.2 Detailed Design Procedure

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

ISO7821 only needs two external bypass capacitors to operate.

GND1

GND2

INB

OUTB

INA

OUTA

GND1

GND2

GND2

VCC2

VCC1

GND1

NC

GND2

9

8

GND1

NC

10

7

NC

NC

11

6

INB

OUTB

12

5

OUTA

INA

13

4

VCC1

VCC2

14

3

NC

NC

15

2

GND1

GND2

16

1

ISO7821DW

0.1 µF

0.1 µF

Figure 8-2. Typical ISO7821 Circuit Hook-up

8.2.2.1 Electromagnetic Compatibility (EMC) Considerations

Many applications in harsh industrial environment are sensitive to disturbances such as electrostatic discharge

(ESD), electrical fast transient (EFT), surge and electromagnetic emissions. These electromagnetic disturbances

are regulated by international standards such as IEC 61000-4-x and CISPR 22. Although system-level

performance and reliability depends, to a large extent, on the application board design and layout, the ISO7821

incorporate many chip-level design improvements for overall system robustness. Some of these improvements

include:

• Robust ESD protection for input and output signal pins and inter-chip bond pads.

• Low-resistance connectivity of ESD cells to supply and ground pins.

• Enhanced performance of high voltage isolation capacitor for better tolerance of ESD, EFT and surge events.

• Bigger on-chip decoupling capacitors to bypass undesirable high energy signals through a low impedance

path.

• PMOS and NMOS devices isolated from each other by using guard rings to avoid triggering of parasitic

SCRs.

• Reduced common mode currents across the isolation barrier by providing purely differential internal

operation.

ISO7821, ISO7821F

SLLSEM2H – NOVEMBER 2014 – REVISED NOVEMBER 2024

www.ti.com

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