JAJSE08D May 2015 – October 2017 TUSB211
PRODUCTION DATA.
8 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.
8.1 Application Information
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.
8.2 Typical Application
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.
Figure 1. Reference Schematic
8.2.1 Design Requirements
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.
8.2.2 Detailed Design Procedure
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.
Table 1. TUSB211 Platform Placement Guideline
| 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 |
NOTE
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:
8.2.2.1 For a Host Side Application
- Configure the TUSB211 to the desired EQ setting
- Power on (or toggle the RSTN pin if already powered on) the TUSB211
- Using SMA cables, connect the oscilloscope and the USB-IF host-side test fixture to the TUSB211
- Enable the host to transmit USB TEST_PACKET
- Execute the oscilloscope’s USB compliance software.
- Repeat the above steps in order to re-test TUSB211 with a different EQ setting
8.2.2.2 For a Device Side Application
- Configure the TUSB211 to the desired EQ setting
- Power on (or toggle the RSTN pin if already powered on) the TUSB211
- Connect a USB host, the USB-IF device-side test fixture, and USB device to the TUSB211. Ensure that the USB-IF device test fixture is configured to the ‘INIT’ position
- Allow the host to enumerate the device
- Enable the device to transmit USB TEST_PACKET
- Using SMA cables, connect the oscilloscope to the USB-IF device-side test fixture and ensure that the device-side test fixture is configured to the ‘TEST’ position.
- Execute the oscilloscope’s USB compliance software.
- Repeat the above steps in order to re-test TUSB211 with a different EQ setting
8.2.3 Application Curves
Figure 2. Eye Diagram Bench Setup
