SLLSEO0D May 2015 – October 2017 TUSB211
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.
The primary purpose of the TUSB211 is to re-store the signal integrity of a USB High Speed channel up to the USB connector. The loss in signal quality stems from reduced channel bandwidth due to high loss PCB trace and other components that contribute a capacitive load. This can cause the channel to fail the USB near end eye mask. Proper use of the TUSB211 can help to pass this eye mask.
A secondary purpose is to use the CD pin and ENA_HS pin of the TUSB211 to control other blocks on the customer platform if so desired.
A typical application is shown below. In this setup, D1P and D1M face the USB connector while D2P and D2M face the USB transceiver. If desired, the orientation may be reversed [that is, D1 faces transceiver and D2 faces connector].
Note that CD and ENA_HS are connected to PLDs. This is for platforms where other circuit blocks must be modified based on the status of the USB channel. They could also be connected to LEDs to give a physical indication of current channel status for debug purposes. If neither use is desired, they can be left floating.
TUSB211 requires a valid reset signal as described in the power supply recommendations section. The capacitor C4 is not required if a microcontroller drives the RSTN pin according to recommendations.
Pin 11 VREG is an internal LDO output that requires a 0.1 μF external capacitor to GND to stabilize the core.
Pin 6 EQ requires an external pulldown resistor if EQ levels 0-2 are needed. If EQ level 3 is needed, then the EQ pin can be left floating.
The ideal EQ setting is dependent upon the signal chain loss characteristics of the target platform. The general recommendation is to start with EQ level 0, and then increment to EQ level 1, and so on. if permissible.
In order for the TUSB211 to recognize any change to the EQ setting, the RSTN pin must be toggled. This is because the EQ pin is latched on power up and the pin is ignored thereafter.
In addition, TUSB211 does not compensate for any DC attenuation in the signal path. Therefore, minimizing DC loss (that is, resistance) in the system design, is suggested. As a consequence, this might lead to increased line capacitance. This is acceptable because the TUSB211 can compensate for the additional capacitive load.
Placement of the device is also dependent on the application goal. Table 1 summarizes the recommendations.
|PLATFORM GOAL||SUGGESTED TUSB211 PLACEMENT|
|Pass USB Near End Mask||Close to measurement point|
|Pass USB Far End Eye Mask||Close to USB PHY|
|Cascade multiple 211s to improve device enumeration||Midway between each USB interconnect|
USB-IF certification tests for High Speed eye masks require the mandated use of the USB-IF developed test fixtures. These test fixtures do not require the use of oscilloscope probes. Instead they use SMA cables. More information can be found at the USB-IF Compliance Updates Page. It is located under the ‘Electricals’ section, ID 86 dated March 2013.
The following procedure must be followed before using any oscilloscope compliance software to construct a USB High Speed Eye Mask: