USB2524 datasheet(4/58 Pages) MICROCHIP

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USB2524

DS00001588B-page 4

 2013 - 2016 Microchip Technology Inc.

1.0

GENERAL DESCRIPTION

The Microchip 4-Port USB 2.0 Switching Hub Controller acts as two independently controllable USB 2.0 Hubs in a single

package with the ability to electronically reassign and reconfigure any of its 4 downstream ports to either of its two

upstream USB ports. This allows two USB hosts to share peripherals and to dynamically reconfigure them.

Any configuration of the downstream ports is possible except simultaneous connection to both upstream ports. Up to 8

different configurations can be selected by a dedicated 3-pin interface, or the 4-pin interface can be used to directly

assign each port to either of the upstream hosts. An external serial EEPROM (or SMBus Host) is used to store the 8

different configuration parameters. However, 8 predefined configurations, as well as generic VID/PID/DID information,

are provided as defaults if no external Serial EEPROM is detected at power up. The SMBus interface can be used to

configure the hub as well as dynamically re-assigning downstream ports to upstream hosts. The SMBus interface can

be “live” while the hub is operational, and allows an external SMBus host to have full access to re-assign ports on an

as-needed basis.

The Microchip 4-Port Switching Hub is fully compliant with the USB 2.0 Specification and will attach to either or both

upstream USB hosts as a Full-Speed Hub or as a Full-/High-Speed Hub. The 4 downstream Hub ports support Low-

Speed, Full-Speed, and High-Speed (if operating as a High-Speed Hub) downstream devices on all of the enabled

downstream ports.

A USB peripheral or USB Hub that is attached to one of the downstream USB2524 ports will be available to one or the

other of the upstream USB host controllers, but can never be simultaneously shared with both host controllers. The user

can switch a peripheral from one host to the other (on-the-fly), and the peripheral will automatically detach from one host

and attach to the other host. Each host will only configure and control the downstream ports that are assigned to it,

including full USB power management and suspend/resume operations.

The USB2524 works with an external USB power distribution switch device to control VBUS switching to downstream

ports, and to limit current and sense over-current conditions.

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.

Throughout this document the upstream facing port of the hub will be referred to as the upstream port, and the down-

stream facing ports will be called the downstream ports.

For performance reasons, the Hub provides 1 Transaction Translator (TT) per port (defined as Multi-TT configuration),

and each TT has 1512 bytes of periodic buffer space and 272 Bytes of non- periodic buffer space (divided into 4 non-

periodic buffers per TT), for a total of 1784 bytes of buffer space for each Transaction Translator.

When configured as a Single-TT Hub (required by USB 2.0 Specification), the Single Transaction Translator will have

1512 bytes of periodic buffer space and 272 bytes of non-periodic buffer space (divided into 4 non-periodic buffers per

TT), for a total of 1784 bytes of buffer space for the entire Transaction Translator.

1.1

OEM Selectable Features

A default configuration is available in the USB2524 following a reset. This configuration may be sufficient for some appli-

cations. Strapping option pins make it possible to modify a limited sub-set of the configuration options.

The USB2524 may also 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 USB2524 supports several OEM selectable features:

• Optional OEM configuration via I2C EEPROM or via the industry standard SMBus interface from an external

SMBus Host or Microcontroller.

• Compound device support (port is permanently hardwired to a downstream USB peripheral device).

• Hardware strapping options enable configuration of the following features (when not configured via an EEPROM

or SMBus host).

- Non-Removable Ports

- Port Power Polarity (active high or active low logic)

• Selection of Single (STT) or Multi-Transaction Translator (MTT) capability.

• Selection of Over-Current sensing and Port power control on a individual (port-by-port) or ganged (all ports

together) to match the OEM’s choice of circuit board component selection.

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