9 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.

9.1 Application Information

9.1.1 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 9-1, the coupling capacitors are placed

between the switch and endpoint. In this situation, the switch is biased by the system/host controller.

Device/

Endpoint

RX

TX

Device/

Endpoint

RX

TX

Port A

Port A

Port B

Port B

System/Host

Controller

RX

TX

Figure 9-1. AC Coupling Capacitors Between Switch TX and Endpoint TX

In Figure 9-2, 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.

Device/

Endpoint

RX

TX

Device/

Endpoint

RX

TX

Port A

Port A

Port B

Port B

System/Host

Controller

RX

TX

Figure 9-2. AC Coupling Capacitors on Host TX and Endpoint TX

HD3SS212

SLAS822D – DECEMBER 2011 – REVISED DECEMBER 2020

www.ti.com

12

Submit Document Feedback

Copyright © 2020 Texas Instruments Incorporated