Usb Port Connector - Noise Filtering; Hub Configuration; Optional Serial Eeprom; Power/Reset - Texas Instruments TUSB8040AEVM User Manual

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VBUS, sourced by the 5-V wall power input, J6, is provided to the downstream port connectors so that bus
powered devices may be attached to the downstream ports. The USB 3.0 specification limits the current
consumption of a USB 3.0 device to 900 mA at 5 V. The current limiting parameter of the TPS2560
devices, U19 and U21, is configured to 1.5 A to avoid any spurious over-current events due to bus-
powered HDD spin-up power fluctuations (SLVS930). A production implementation could place stricter
limits on this power consumption. An over-current event on any of the downstream port connectors will be
reported to the TUSB8040A via the OVERCURxZ inputs.
2.2 USB Port Connector – Noise Filtering
Each downstream VBUS output has a 150-µF bulk capacitor (C65, C67, C72, C75) as recommended by
the TPS2560 data manual 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.
The TUSB8040AEVM also implements optional isolation using two small noise filtering capacitors and a
1-MΩ resistor between the earth ground of each connector and the digital ground of the EVM, this is not a
requirement but should be used if ground isolation is desired.
Please note that the series capacitors implemented on the SS TX pairs are incorporated to satisfy the
USB 3.0 requirement that differential links be AC coupled on the transmit pair.
3

Hub Configuration

The TUSB8040AEVM can be configured by setting several inputs to the TUSB8040A that are sampled at
power-on reset or using an optional serial EEPROM. See section 3.1 for a full description of these inputs
and how to configure them. A production implementation would either rely on the default internal pull-up or
pull-down resistor for each configuration input or over-ride it with an external pull-up or pull-down resistor.
4

Optional Serial EEPROM

Each TUSB8040AEVM is equipped with an onboard EEPROM/socket placeholder. A small I
can be installed to set the configuration registers as defined in the TUSB8040A data manual (SLLSEA7).
In its default setting, the EVM does not have an EEPROM installed and instead uses the configuration
inputs to determine any optional settings of the TUSB8040A.
The EEPROM interface defaults to programmable (not write-protected) so that any installed EEPROM's
contents may be modified to test various settings. If an EEPROM data change is required, the values may
be changed using the register access methods outlined in the TUSB8040A data sheet (SLLSE97). In
addition, a Windows
5

Power/Reset

The TUSB8040AEVM operates from the power provided by a 5-V wall power adapter, not bus power
supplied by a USB host. It is recommended to use a wall power adapter that is capable of sourcing 4 A to
5 A because the hub must be able to source significant power on its downstream ports (900 mA per port).
The TUSB8040AEVM uses a single channel LDO voltage regulator to drop 5 V to 3.3 V. The TPS7A4533,
U20, is a 1.5-A output linear regulator (SLVS720). The 1.1-V core voltage required by the TUSB8040A is
sourced by the 3.3-V rail to reduce unnecessary heat dissipation. The TPS74801, U22, is a 1.5-A output
single channel LDO linear regulator (SBVS074). Both regulators require few external passive components
and are appropriately rated for heat dissipation.
While there are two power-on reset sources on the TUSB8040AEVM, only one is required. Implemented
on the EVM is a supervisory circuit, TPS3808G33, U2 (SBVS050). This device has two input sources: the
BOARD_3P3V power rail and the 1.1-V regulator power good output. The other reset source is the RC
circuit created by the internal pull-up resistor of GRSTz and the 1-µF capacitor, C18. If R4-R7, C16 and
C17 are installed, the reset supervisor circuit is enabled. If those passive components are not populated,
the RC circuit is enabled.
The TUSB8040A requires a power on reset of 3 ms, the value of the capacitor used in the RC circuit
would vary based on the voltage ramp characteristics of the implementation.
SLLU163 – May 2012
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Copyright © 2012, Texas Instruments Incorporated
Hub Configuration
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C EEPROM
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