Datasheet

USB 2.0 Hi-Speed Hub Controller
Datasheet
Revision 2.2 (02-17-12) 22 SMSC USB251xB/xBi
DATASHEET
3.3.1 Configuring the Strap Pins
If a pin's strap function is enabled thru the hub configuration selection, (Table 5.1: Initial
Interface/Configuration Options on page 26) the strap pins must be pulled either high or low using the
values provided in Tab le 3. 4. Each strap option is dependent on the pin’s buffer type, as outlined in
the sections that follow.
3.3.1.1 Non-Removable
If a strap pin’s buffer type is I/O, an external pull-up or pull-down must be implemented as shown in
Figure 3.4. Use Strap High to set the strap option to 1 and Stap Low to set the strap option to 0. When
implementing the Strap Low option, no additional components are needed (i.e., the internal pull-down
provides the resistor)
Figure 3.4 Non-Removable Pin Strap Example
3.3.1.2 Internal Pull-Down (IPD)
If a strap pin’s buffer type is IPD (pins BC_EN[x:1]), one of the two hardware configurations outlined
below must be implemented. Use the Strap High configuration to set the strap option value to 1 and
Strap Low to set the strap option value to 0.
Figure 3.5 Pin Strap Option with IPD Pin Example
Table 3.4 Strap Option Summary
STRAP OPTION RESISTOR VALUE BUFFER TYPE NOTES
Non-Removable 47 - 100 kΩ I/O
Internal Pull-Down
10 kΩ IPD
 Only applicable to port power pins
 Contains a built-in resistor
LED 47 - 100 kΩ I/O
HUBHUB
I/O Strap Pin Strap High
+V
I/O Strap Pin
Strap Low
GND
R kΩ
R kΩ
HUBHUB
IPD Strap Pin Strap High
R kΩ
+V
VSS
IPD Strap Pin Strap Low
VSS