Texas Instruments TUSB8020BPHP REVA User Manual page 4

The TUSB8020B EVM board hardware is divided into the following functional areas:
1 TUSB8020BPHP
The TUSB8020B on the TUSB8020B EVM (U2 on the schematic) operates as a functional interconnect
between an upstream connection to a USB host or hub and up to two directly connected downstream
devices or hubs. More devices and hubs can be supported, if arranged in tiers. The TUSB8020B is
capable of supporting operation at USB SuperSpeed (SS), High-Speed (HS), Full Speed (FS) or Low
Speed (LS). In general, the speed of the upstream connection of the TUSB8020B EVM limits the
downstream connections to that speed (SS, HS, and FS) or lower.
The TUSB8020B requires a 24-MHz low ESR crystal, Y1 with a 1-MΩ feedback resistor. The crystal
should be fundamental mode with a load capacitance of 12 pF – 24 pF and a frequency stability rating of
±100 PPM, or better. To ensure a proper startup oscillation condition, a maximum crystal equivalent series
resistance (ESR) of 50 Ω is recommended.
The TUSB8020B can also use an oscillator or other clock source. When using an external clock source
such as an oscillator, the reference clock should have ±100 PPM (or better) frequency stability and have
less than 50-ps absolute peak- to-peak jitter (or less) than 25-ps peak-to-peak jitter after applying the USB
3.0 jitter transfer function.
2 USB Port Connectors
The TUSB8020B EVM is equipped with three standard nine pin USB 3.0 port connectors. One of these
three connectors, J3, is a Type B connector designed to interface with an upstream USB host or hub. The
remaining connectors, J1 and J4, are Type A connectors for connection to downstream devices or hubs.
Standard size connectors were used on the EVM design, but USB micro connectors can be used if
desired. It is also possible to implement a legacy USB connector on one or more of the downstream ports
if SuperSpeed operation is not desired.
The USB ports can be attached via a standard USB cable to any USB 3.0 or legacy USB host, hub or
device. The TUSB8020B automatically connects to any upstream USB 3.0 host or hub at both
SuperSpeed and High-Speed. Using a legacy USB cable between the TUSB8020B EVM and a USB 3.0
host or hub forces it to High-Speed operation. The same is true if a legacy USB cable is used between the
TUSB8020B EVM and a downstream SuperSpeed capable device: operation is limited to USB 2.0 High-
Speed.
2.1 USB Port Connector - Power
VBUS is received from the upstream host or hub on J3. The TUSB8020B is configured as a self-powered
hub, so there is not any significant current draw by the EVM from VBUS. The TUSB8020B does monitor
the VBUS input after filtering through a resistor divider network of a 90.9-kΩ, 1% resistor, R9, and a 10-
kΩ, 1% resistor, R10. VBUS cannot be directly connected to the TUSB8020B device. A bulk capacitor of
at least 1 μF is required on the upstream port VBUS input to comply with the USB specification. The
TUSB8020BEVM uses a 10-μF capacitor, C8.
2.2 USB Port Connector – Noise Filtering
Each downstream VBUS output has a 150-μF bulk capacitor (C49, C51) as recommended by the
TPS2561 data manual (SLVS930) to prevent in-rush current events on the downstream devices. In
addition, there are ferrite beads and small capacitors on the VBUS lines to reduce noise and address
ESD/EMI concerns.
4
Hardware Overview
Copyright © 2014, Texas Instruments Incorporated
SLLU196 – March 2014
Hardware Overview
SLLU196 – March 2014
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