HD3SS3212_15 Datasheet, PDF (10/25 Pages) Texas Instruments – HD3SS3212x Two-Channel Differential 2:1/1:2 USB3.1 Mux/Demux

HD3SS3212, HD3SS3212I
SLASE74A – MAY 2015 – REVISED AUGUST 2015
10 Application and Implementation
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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
The HD3SS3212 is a generic 2-channel high-speed mux/demux type of switch that can be used for routing high-
speed signals between two different locations on a circuit board. The HD3SS3212 supports several high-speed
data protocols with a differential amplitude of <1800 mVpp and a common mode voltage of <2.0 V, as with USB
3.0 and DisplayPort 1.2. The device’s one select input (SEL) pin can easily be controlled by an available GPIO
pin within a system or from a microcontroller.
The HD3SS3212 with its adaptive common mode tracking technology can support applications where the
common mode is different between the RX and TX pair. The two USB3.1 Type C connector applications show
both a host and device side. The cable between the two connectors swivels the pairs to properly route the
signals to the correct pin. The other applications are more generic because different connectors can be used.
Many interfaces require AC coupling between the transmitter and receiver. The 0402 capacitors are the preferred
option to provide AC coupling; 0603 size capacitors also work. Avoid the 0805 size capacitors and C-packs.
When placing AC coupling capacitors, symmetric placement is best. A capacitor value of 0.1 µF is best, and the
value should match for the ±signal pair. The designer should place them along the TX pairs on the system board,
which are usually routed on the top layer of the board.
The AC coupling capacitors have several placement options. Because the switch requires a bias voltage, the
designer must place the capacitors on one side of the switch. If they are placed on both sides of the switch, a
biasing voltage should be provided. Figure 4 shows a few placement options. The coupling capacitors are placed
between the switch and endpoint. In this situation, the switch is biased by the system/host controller.
TX
System/Host
controller
RX
Port B
Port C
Port B
Port C
0.1 µF
0.1 µF
0.1 µF
0.1 µF
RX
Device/
Endpoint
TX
RX
Device/
Endpoint
TX
Figure 4. AC Coupling Capacitors between Switch TX and Endpoint TX
In Figure 5, the coupling capacitors are placed on the host transmit pair and endpoint transmit pair. In this
situation, the switch on top is biased by the endpoint and the lower switch is biased by the host controller.
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