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ISO7820LL, ISO7821LL

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SLLSET8A – MARCH 2016 – REVISED AUGUST 2016

Product Folder Links: ISO7820LL ISO7821LL

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Copyright © 2016, Texas Instruments Incorporated

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 ISO782xLL is a family of high-performance, reinforced isolated dual-LVDS buffers. Isolation can be used to

help achieve human and system safety, to overcome ground potential difference (GPD), or to improve noise

immunity and system performance.

The LVDS signaling can be used over most interfaces to achieve higher data rates because the LVDS is only a

physical layer. LVDS can also be used for a proprietary communication scheme implemented between a host

controller and a slave. Example use cases include connecting a high-speed I/O module to a host controller, a

subsystem connecting to a backplane, and connection between two high-speed subsystems. Many of these

systems operate under harsh environments making them susceptible to electromagnetic interferences, voltage

surges, electrical fast transients (EFT), and other disturbances. These systems must also meet strict limits on

radiated emissions. Using isolation in combination with a robust low-noise signaling standard such as LVDS,

achieves both high immunity to noise and low emissions.

Example end applications that could benefit from the ISO782xLL family of devices include high-voltage motor

control, test and measurement, industrial automation, and medical equipment.

9.2 Typical Application

One application for isolated LVDS buffers is for point-to-point communication between two high-speed capable,

application-specific integrated circuits (ASICs) or FPGAs. In a high-voltage motor control application, for

example, Node 1 could be a controller on a low-voltage or earth referenced board, and Node 2, could be

controller placed on the power board, biased to high voltage. Figure 29 and Figure 30 show the application

schematics.

Figure 30 provides further details of using the ISO782xLL family of devices to isolate the LVDS interface. The

LVDS connection to the ISO782xLL family of devices can be traces on a board (shown as straight lines between

Node 1 and the ISO782xLL device), a twisted pair cable (as shown between Node 2 and the ISO782xLL device),

or any other controlled impedance channel. Differential 100-

Ω terminations are placed near each LVDS receiver.

The characteristic impedance of the channel should also be 100-

Ω differential.

In the example shown in Figure 29 and Figure 30, the ISO782xLL family of devices provides reinforced or safety

isolation between the high-voltage elements of the motor drive and the low-voltage control circuitry. This

configuration also ensures reliable communication, regardless of the high conducted and radiated noise present

in the system.