HD3SS3412_16 Datasheet, PDF (15/27 Pages) Texas Instruments – 4-Channel High-Performance Differential Switch

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10 Application and Implementation
HD3SS3412
SLAS828E – FEBRUARY 2012 – REVISED JANUARY 2016
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.
10.1 Application Information
10.1.1 AC Coupling Caps
Many interfaces require AC coupling between the transmitter and receiver. The 0402 capacitors are the preferred
option to provide AC coupling, and the 0603 size capacitors also work. The 0805 size capacitors and C-packs
should be avoided. When placing AC coupling capacitors symmetric placement is best. A capacitor value of 0.1
µF is best and the value should be match for the ± signal pair. The placement should be along the TX pairs on
the system board, which are usually routed on the top layer of the board.
There are several placement options for the AC coupling capacitors. Because the switch requires a bias voltage,
the capacitors must only be placed on one side of the switch. If they are placed on both sides of the switch, a
biasing voltage should be provided. A few placement options are shown below. In Figure 11, the coupling
capacitors are placed between the switch and endpoint. In this situation, the switch is biased by the system/host
controller.
Figure 11. AC Coupling Capacitors Between Switch Tx and Endpoint Tx
In Figure 12, the coupling capacitors are placed on the host transmit pair and endpoint transmit pair. In this
situation, the switch on the top is biased by the endpoint and the lower switch is biased by the host controller.
Figure 12. AC Coupling Capacitors on Host Tx and Endpoint Tx
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