Datasheet

USB251xB/xBi
DS00001692C-page 4  2010 - 2015 Microchip Technology Inc.
1.0 INTRODUCTION
The Microchip USB251xB/xBi hub family is a group of low-power, configurable, MTT (multi transaction translator) hub
controller ICs. The hub provides downstream ports for embedded USB solutions and is fully compliant with the USB 2.0
Specification [1]. Each of the hub controllers can attach to an upstream port as a full-speed or full-/hi-speed hub. The
hub can support low-speed, full-speed, and hi-speed downstream devices when operating as a hi-speed hub.
All required resistors on the USB ports are integrated into the hub. This includes all series termination resistors 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 USB251xB/xBi hub family includes programmable features, such as:
• MultiTRAK
TM
Technology: implements a dedicated Transaction Translator (TT) for each port. Dedicated TTs help
maintain consistent full-speed data throughput regardless of the number of active downstream connections.
• PortMap: provides flexible port mapping and disable sequences. The downstream ports of a USB251xB/xBi hub
can be reordered or disabled in any sequence to support multiple platform designs with minimum effort. For any
port that is disabled, the USB251xB/xBi hub controller automatically reorders the remaining ports to match the
USB host controller’s port numbering scheme.
• 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: enables 4 programmable levels of USB signal drive strength in downstream port transceivers. PHY-
Boost will also attempt to restore USB signal integrity.
1.1 Configurable Features
The USB251xB/xBi hub controller provides a default configuration that may be sufficient for most applications. Strapping
option pins (see Section 3.3.1 on page 14) provide additional features to enhance the default configuration. When the
hub is initialized in the default configuration, the following features may be configured using the strapping options:
• Downstream non-removable ports, where the hub will automatically report as a compound device
• Downstream disabled ports
• Enabling of battery charging option on individual ports
• The USB251xB/xBi hub controllers can alternatively be configured by an external I
2
C EEPROM or a microcontrol-
ler as an SMBus slave device. When the hub is configured by an I
2
C EEPROM or over SMBus, the following con-
figurable features are provided:
• Support for 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 circuit board
component selection
• Customizable vendor ID, product ID, and device ID
• Configurable USB signal drive strength
• Configurable USB differential pair pin location
• Configurable delay time for filtering the over-current sense inputs
• Configurable downstream port power-on time reported to the host
• Indication of the maximum current that the hub consumes from the USB upstream port
• Indication of the maximum current required for the hub controller
• Custom string descriptors (up to 31 characters):
- Product
- Manufacturer
- Serial number
• Battery charging USB251xB/xBi products are fully footprint compatible with USB251x/xi/xA/xAi products:
-Pin-compatible
- Direct drop-in replacement
- Use the same PCB components
- USB-IF Compliance by Similarity for ease of use and a complete cost reduction solution
- Product IDs, device IDs, and other register defaults may differ. See Section 5.1 on page 19 for details.