SLASEW5 December 2020 TMUXHS4412
The TMUXHS4412 is an analog 4-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 TMUXHS4412 can be used for many high speed interfaces including:
The device’s mux/demux selection pin SEL can easily be controlled by an available GPIO pin of a controller or hard tie to voltage level H or L as an application requires.
The TMUXHS4412 with adaptive voltage tracking technology can support applications where the common mode is different between the RX and TX pair. The switch paths of the TMUXHS4412 have internal weak pull-down resistors of 1 MΩ on the common port pins. While these resistors biases the device data channels to common mode voltage (CMV) of 0 V with a weak strength, it is recommended that the device is biased from either side of the device to a valid value (in the range of 0 - 1.8 V in 3.3 V supply voltage mode). It is expected that the system/host controller and Device/End point common mode bias impedances are much stronger (smaller) than the TMUXHS4412 internal pull-down resistors; therefore, they are not impacted.
Many interfaces require AC coupling between the transmitter and receiver. The 0201 or 0402 capacitors are the preferred option to provide AC coupling. Avoid the 0603, 0805 size capacitors and C-packs. When placing AC coupling capacitors, symmetric placement is best. The capacitor value must be chosen according to the specific interface the device is being used. The value of the capacitor should match for the positive and negative signal pair. For many interfaces such as USB 3.2 and PCIe, the designer should place them along the TX pairs on the system board, which are usually routed on the top layer of the board. Depending upon the application and interface specifications, use the appropriate value for AC coupling capacitors.
The AC coupling capacitors have several placement options. Typical use cases warrant that the capacitors are placed on one side of the TMUXHS4412. In certain use cases, if both side of the TMUXHS4412 is ac coupled, it is recommended that appropriate CMV biasing is used for the device. 10 kΩ to GND or any other bias voltage in the valid CMV range for each D[0/1/2/3][P/N] pin of the common port suffice for most use cases. Figure 8-1 shows a few placement options. Note for brevity not all channels are illustrated in the block diagrams. Some interfaces such as USB SS and PCIe recommends AC coupling capacitors on the TX signals before it goes to a connector. Option (a) features TX AC coupling capacitors on the connector side of the TMUXHS4412. Option (b) illustrates the capacitors on the host of the TMUXHS4412. Option (c) showcases where the TMUXHS4412 is ac coupled on both sides. VBIAS must be within the valid CMV of the device.