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TUSB1002A

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SLLSF63 – MARCH 2018

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emphasis pre-compensates for the loss of the output channel. With 3 dB of de-emphasis, the total equalization

required by the TUSB1002A is in the 5.2 dB (8.2 dB - 3 dB) range. The channel A-B for this example is

connected to TUSB1002A's RX1P/N input and therefore CH1_EQ[2:1] pins are used for adjusting TUSB1002A

RX1P/N equalization settings. The CH1_EQ[2:1] pins should be set such that TUSB1002A equalization is

between 5dB and 8dB.

The channel C-D has a trace length of 2 inches with a 4mil trace width. Assuming 0.83 dB per inch of insertion

loss, the 2 inch trace will equate to about 1.66 dB of loss at 5 GHz. An additional 2dB of loss needs to be added

due to package, A/C coupling capacitor, and the USB 3.1 receptacle. The total loss is around 3.66 dB. Because

channel C-D includes a USB 3.1 receptacle, the actual total loss could be much greater than 3.66dB due to the

fact that devices plugged into the receptacle will also have loss. The device plugged into receptacle will have

either a short or long channel. USB3.2 standard defines total loss limit of 23dB that is distributed as 8.5 dB for

Host, 8.5dB for device, and 6.0dB for cable. With variable channel of devices plugged into the USB3.2

receptacle, configuring TUSB1002A's RX2P/N equalization settings is not as straight forward as Channel A-B.

Engineer can not set TUSB1002A CH2_EQ[2:1] pins to the largest equalization setting to accommodate the

largest allowed USB3.2 device/cable loss of 14.5 dB. Doing so will result in TUSB1002A operating outside its

linear range when a device with short channel is plugged into the receptacle. For this reason, it is recommended

to configure TUSB1002A CH2_EQ[2:1] pins to equalize a shorter device channel. This will result in requiring

USB3.2 host to compensate for remaining channel loss for the worse case USB3.2 channel of 14.5 dB. The

definition of a short device channel is not specified in USB 3.1 specification. Therefore, an engineer must make

their own loss estimate of what constitutes a short device channel. For particular example, we will assume the

short channel is around 2 to 3 dB. The device's channel loss will need to be added to estimated Channel C-D

loss minus the typical 3db of de-emphasis. This means CH2_EQ[2:1] pins should be configured to handle a loss

of 3 to 5 db.

8.2.3 Application Curves

Freq = 5 GHz

dB(SDD21) = –6.666

Figure 19. Insertion Loss for 8inch 4 mil FR4 Trace