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Figure 2. Circuit for isolated LVDS wiring with the ADN4651 four-channel isolator, two transmission channels,
and two reception channels. This permits signal
the wiring. The ADN465x family works internally transmission by means of two complete
with a supply voltage of 2.5V; industrial systems transmission and reception channels on only one
often, unfortunately, do not have this supply electronic assembly with simultaneously very high
voltage, but rather often only 3.3V, available. For transmission rates.
this reason, low dropout voltage regulators (LDOs) The data rates of almost dc up to 600 Mbps can
enabling an external supply voltage of 3.3V at the easily be reached with the ADN465x family
inputs are integrated into the ADN465x family. The provided that the specifications for the maximum
supply to the module or its inputs and its isolated pulse width distortion are adhered to. In addition, a
output side can, for example, be accomplished with few factors necessary for transmission of differential
the isolated ADuM5000 dc-to-dc converter. This signals at high speeds must be taken into
can selectively generate an isolated output voltage consideration in the layout. Thus, the input- and
of either 5V or 3.3V with a maximum power output output-side traces should be matched and exhibit
of 500mW. This circuit configuration is shown in an approximate impedance of 50Ω with respect to
Figure 1. ground or 100Ω between the signal lines. Further-
In combination with the ADuM5000, this device more, it is advisable to attach 100Ω terminators to
family can meet the numerous demands placed on the LVDS inputs, as shown in Figure 2.
isolated LVDS interfaces in today’s industrial The cable length and the connector type also
applications. This highly integrated solution also affect the maximum data rate. Lower data rates of
meets all prerequisites for standardised bus up to 200 Mbps in combination with connectors for
communications. LVDS interfaces are frequently high data rates and shielded wire pairs even enable
used in energy-saving applications. For this, the cable lengths of several meters.
combination of the ADN4651 and the ADuM5000 The ADN4650/ADN4651/ADN46521 are
represents an extremely power-saving alternative to signal isolated, LVDS buffers that operate at up to
traditional optocoupler solutions. The simultaneous 600 Mbps with very low jitter. This combination
isolation of several channels is often also required. with the ADuM5000 makes it ideal for high speed
In LVDS applications, channels are used in signal transmissions by being able to achieve 600
parallel to maximise the throughput and, with it, the Mbps for short distances and 200 Mbps for up to
baud rate. The described circuit with the above- several metres.
mentioned modules from Analog Devices offers one www.analog.com

July 2020 • INDUSTRIAL TECHNOLOGY EXTRA! • p7