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TUSB542: Guidelines for Determining AP-Side EQ Settings on TUSB542

user6323968
Prodigy 70 points

Part Number: TUSB542

I have a question regarding the EQ setting on the AP side of the TUSB542.
 
For the connector side, we can determine the optimal EQ setting through compliance testing and signal quality measurements. However, for the AP side (SoC to TUSB542), it is often difficult to perform detailed signal integrity evaluation because compliance test patterns may not be available from the SoC in the final system.
 
Does TI have any guideline, recommendation, or evaluation data for selecting the AP-side EQ setting?
 
For example:
 
- Recommended EQ settings based on PCB trace length
- Recommended EQ settings based on channel insertion loss
- Results from TI reference designs or evaluation boards
- The channel conditions assumed for the default setting (CTL0/CTL1 floating)
 
Any guidance would be appreciated.
  • 0
    TI__Guru 60936 points

    Hi,

    You can use the TUSB542 as a reference design: https://www.ti.com/tool/TUSB542EVM

    Keep in mind that the TUSB542 will be able to compensate for the green regions, but the red regions will need to be compensated by the USB host/ device. 

    the upstream connection can be tuned using electrical results for TX eye diagrams.

    The downstream connection is more difficult as this needs to be tuned using the RX jtol test. 

    A good rule of thumb for FR4 PCBs is 0.2 dB/in/GHz. at 5Gbps signaling the fundamental frequency is 2.5GHz. This means a loss of .5dB per inch of PCB trace. vias and connectors add approx. 0.5 dB each. 

    Using the insertion loss generated from this approximation. The TUSB542 equalization can be tuned to compensate for this loss. Keep in mind that a signal can become overcompensated, so maxing out the EQ is not the best option. 

    user6323968 said:
    The channel conditions assumed for the default setting (CTL0/CTL1 floating)

    The default configuration is based on the sampled configuration pins at startup. 

  • 0 in reply to Vishesh Pithadiya
    Prodigy 70 points

    Hi,

    Thank you for the reply.

    As a general guideline, at what channel insertion loss (at 2.5 GHz) would you typically start increasing the EQ setting from the default configuration?

    I understand that the exact value depends on the system and PHY characteristics, but I would appreciate any rule-of-thumb based on TI's experience.

    Regard.

  • 0 in reply to user6323968
    TI__Guru 60936 points

    Hi,

    If the default state is FF for SNFG1 and CNFG2, then the settings will be as follows:

    For a source applications the signal path is as follows:

    USB Host -----(pre-channel)----> redriver -------(post-channel) -----> Connector

    The pre-channel compensation will be 0dB, and the post channel compensation will be 6dB.

    It's typically best to place the redriver close to the connector, so there is no uncompensated loss. This means that pre-channel loss > post-channel loss.

    for every 4-6 inches of trace the equalization will need to be stepped up by 3dB.

    What is the board size you are designing?

    What are the expected pre-channel and post channel losses?

  • 0 in reply to Vishesh Pithadiya
    Prodigy 70 points

    Hi,

    Thank you for the explanation.

    The estimated pre-channel length (USB Host to TUSB542) is approximately 4 inches, and the post-channel length (TUSB542 to the connector) is approximately 1 inch.

    Based on your guideline that the EQ should be increased by approximately 3 dB for every 4 to 6 inches of trace length, our understanding is that the default EQ setting should be sufficient for this design and that no additional AP-side EQ adjustment is required.

    Regards,

  • +1 in reply to user6323968
    TI__Guru 60936 points

    Hi,

    This is just an estimation, real world losses may be higher or lower. In the case of a 4in pre-channel and 1in post channel, I would test with the following settings, but additional tuning may be required.

  • 0 in reply to Vishesh Pithadiya
    Prodigy 70 points

    Hi,

    Thank you for the reply.

    I got it.

    Regards.