System/Host

controller

RX

Device/

Endpoint

RX

Device/

Endpoint

RX

Port B

Port B

Port C

Port C

0.1 F

µ

0.1 F

µ

0.1 µF

0.1 F

µ

TX

TX

TX

HD3SS3212, HD3SS3212I

SLASE74C – MAY 2015 – REVISED JANUARY 2016

www.ti.com

10 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.

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.

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.

10

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