USB 2.0 High-Speed 2-Port Hub Controller
Datasheet
Chapter 2 General Description
The SMSC USB251x hub family is a group of low-power, OEM configurable, MTT (multi
transaction translator)1 hub controller IC’s with downstream ports for embedded USB solutions.
The SMSC USB251x hub family is fully compliant with the USB 2.0 specification. Each of the
SMSC hub controllers can attach to an upstream port as a full-speed hub or as a full-/hi-speed
hub. The SMSC hub controllers support low-speed, full-speed, and hi-speed (if operating as a
hi-speed hub) downstream devices on all of the enabled downstream ports.
All required resistors on the USB ports are integrated into the hub. This includes all series
termination resistors on D+ and D– pins and all required pull-down and pull-up resistors on D+
and D– pins. The over-current sense inputs for the downstream facing ports have internal pull-
up resistors.
The USB251x hub family includes programmable features such as:
MultiTRAKTM Technology which utilizes a dedicated TT per port to maintain consistent full-
speed data throughput regardless of the number of active downstream connections. MultiTRAKTM
outperforms conventional USB 2.0 hubs with a single TT in USB full-speed data transfers.
PortMap which provides flexible port mapping and disable sequences. The downstream ports of
a USB251x hub can be reordered or disabled in any sequence to support multiple platform
designs with minimum effort. For any port that is disabled, the USB251x hub controllers
automatically reorder the remaining ports to match the USB host controller’s port numbering
scheme.
PortSwap which adds per-port programmability to USB differential-pair pin locations. PortSwap
allows direct alignment of USB signals (D+/D-) to connectors to avoid uneven trace length or
crossing of the USB differential signals on the PCB.
PHYBoost which enables 4 programmable levels of USB signal drive strength in downstream
port transceivers. PHYBoost attempts to restore USB signal integrity.
OEM Selectable Features
A default configuration is available in each of the SMSC USB251x hub controllers following a
reset. This configuration may be sufficient for most applications. Strapping option pins make it
possible to modify a sub-set of the configuration options.
The USB251x hub controllers may be configured by an external EEPROM or a microcontroller.
When using the microcontroller interface, the hub appears as an SMBus slave device. If the hub
is pin-strapped for external EEPROM configuration but no external EEPROM is present, then a
value of ‘0’ will be written to all configuration data bit fields (the hub will attach to the host with
all ‘0’ values).
The USB251x hub family supports OEM selectable features including:
Optional OEM configuration via I2C EEPROM or via the industry standard SMBus interface
from an external SMBus host or microcontroller.
Supports compound devices on a port-by-port basis.
Selectable over-current sensing and port power control on an individual or ganged basis to
match the OEM’s choice of circuit board component selection.
Customizable vendor ID, product ID, and device ID.
Configurable delay time for filtering the over-current sense inputs.
Configurable downstream port power-on time reported to the host.
Supports indication of the maximum current that the hub consumes from the USB upstream
port.
Supports Indication of the maximum current required for the hub controller.
1.USB2512A/2Ai only uses a single transaction translator.
Revision 1.0 (3-11-09)
8
SMSC USB251x
DATASHEET
SMSC [ SMSC CORPORATION ]
