Datasheet
Table Of Contents
- Chapter 1 USB251x Hub Family Differences Overview
- Chapter 2 General Description
- Chapter 3 Acronyms
- Chapter 4 Block Diagram
- Chapter 5 Pin Descriptions
- Chapter 6 LED Usage Description
- Chapter 7 Battery Charging Support
- Chapter 8 Configuration Options
- Chapter 9 DC Parameters
- 9.1 Maximum Guaranteed Ratings
- 9.2 Operating Conditions
- Figure 9.1 Supply Rise Time Model
- Table 9.1 DC Electrical Characteristics (continued)
- Table 9.2 Supply Current Unconfigured: Hi-Speed Host (ICCINTHS)
- Table 9.3 Supply Current Unconfigured: Full-Speed Host (ICCINTFS)
- Table 9.4 Supply Current Configured: Hi-Speed Host (IHCH1)
- Table 9.5 Supply Current Configured: Full-Speed Host (IFCC1)
- Table 9.6 USB251x/xi/xA/xAi Supply Current Suspend (ICSBY)
- Table 9.7 USB251xB/xBi Supply Current Suspend (ICSBY)
- Table 9.8 USB251x/xi/xA/xAi Supply Current Reset (ICRST)
- Table 9.9 USB251xB/xBi Supply Current Reset (ICRST)
- Table 9.10 Pin Capacitance for USB251x, USB251xi, USB251xA, USB251xAi
- Table 9.11 Pin Capacitance for USB251xB and USB251xBi
- 9.2.1 Package Thermal Specifications
- Chapter 10 AC Specifications
- Chapter 11 Package Outlines

USB 2.0 Hi-Speed Hub Controller
Datasheet
Revision 1.1 (04-26-10) 60 SMSC USB251x
DATASHEET
t2+t3+t4+t5+t6+t7. For Self-Powered configurations, t3 MAX is not applicable and the time to load
the configuration is determined by the external SMBus host.
All power supplies must have reached the operating levels mandated in Chapter 9, DC Parameters,
prior to (or coincident with) the assertion of RESET_N.
8.7.2 USB Bus Reset
In response to the upstream port signaling a reset to the hub, the hub does the following:
Note: The hub does not propagate the upstream USB reset to downstream devices.
1. Sets default address to 0.
2. Sets configuration to: Unconfigured.
3. Negates PRTPWR[x:1] to all downstream ports unless battery charging (BC_EN) is enabled.
4. Clears all TT buffers.
5. Moves device from suspended to active (if suspended).
6. Complies with Section 11.10 of the USB 2.0 specification for behavior after completion of the reset
sequence. The host then configures the hub and the hub’s downstream port devices in accordance
with the USB specification.
Note: The hub does not propagate the upstream USB reset to downstream devices.