Datasheet

100 Ω
Serialized Data
Parallel Data In Parallel Data Out
50 Ω
ASICASIC ASIC ASIC
SN65LV1023A
SN65LV1224B
SLLS621E –SEPTEMBER 2004–REVISED DECEMBER 2009 www.ti.com
APPLICATION INFORMATION
DIFFERENTIAL TRACES AND TERMINATION
The performance of the SN65LV1023A/SN65LV1224B is affected by the characteristics of the transmission
medium. Use controlled-impedance media and termination at the receiving end of the transmission line with the
media’s characteristics impedance.
Use balanced cables such as twisted pair or differential traces that are ran close together. A balanced cable
picks up noise together and appears to the receiver as common mode. Differential receivers reject
common-mode noise. Keep cables or traces matched in length to help reduce skew.
Running the differential traces close together helps cancel the external magnetic field, as well as maintain a
constant impedance. Avoiding sharp turns and reducing the number of vias also helps.
TOPOLOGIES
There are several topologies that the serializers can operate. Three common examples are shown below.
Figure 22 shows an example of a single-terminated point-to-point connection. Here a single termination resistor
is located at the deserializer end. The resistor value should match that of the characteristic impedance of the
cable or PC board traces. The total load seen by the serializer is 100 Ω. Double termination can be used and
typically reduces reflections compared with single termination. However, it also reduces the differential output
voltage swing.
AC-coupling is only recommended if the parallel TX data stream is encoded to achieve a dc-balanced data
stream. Otherwise the ac-capacitors can induce common mode voltage drift due to the dc-unbalanced data
stream.
Figure 22. Single-Terminated Point-to-Point Connection
Figure 23 shows an example of a multidrop configuration. Here there is one transmitter broadcasting data to
multiple receivers. A 50-kΩ resistor at the far end terminates the bus.
Figure 23. Multidrop Configuration
Figure 24 shows an example of multiple serializers and deserializers on the same differential bus, such as in a
backplane. This is a multipoint configuration. In this situation, the characteristic impedance of the bus can be
significantly less due to loading. Termination resistors that match the loaded characteristic impedance are
required at each end of the bus. The total load seen by the serializer in this example is 27 Ω.
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