Chapter 2
Hardware Overview
The USB keyboard/hub EVM is 4-inches L × 3.5-inches W and features the TPS2149 made by Texas Instruments. The TPS2149 is a power management device that integrates an LDO and two power switches into one small package. Jumpers (0-Ω resistors) and jumper blocks provided on the EVM are installed with the factory settings. The settings are described in Table 3–2. Review all setting changes prior to powering the EVM. Improper settings could result in damage to some of the EVM components. The factory settings allow the EVM to operate using a 12-MHz crystal along with an I2C EEPROM. The EVM has also been configured to work only in bus-powered mode. The firmware installed at the factory and stored in the EEPROM will allow the EVM to function as a two port keyboard hub. Users are responsible for developing their own application firmware for the target hardware device.
The EVM also uses a TUSB2136, USB keyboard/hub controller, made by Texas Instruments, to communicate with the host and the downstream devices. A USB cable is needed to connect the root hub of the PC to the EVM type B connector (J5). The downstream devices connect to the EVM via the J6 and J7 connectors. These downstream devices are powered through the TPS2149. The USB specifications require that downstream ports remain off until enumeration is complete. Together, the TUSB2136 and the TPS2149 ensure the hub meets this requirement. Two other connectors, J3 and J4, allow easy connection to the TUSB2136 general-purpose I/O lines. These lines can be used to implement the keyboard function.
Jumpers, test points, and LEDs have been added for testing, troubleshooting and debugging purposes. Most of the test points are located near the TPS2149. There are also test points on the differential pair lines of the upstream B-type connector and the two downstream A-type connectors. The I2C port can be probed directly on the EEPROM. Six LEDs are provided for quick feedback during firmware debugging or as status information. One LED (D1) is fixed to provide power and suspend status of the TUSB2136 device.
