USB 2.0 Hi-Speed Hub Controller
Datasheet
Table 5.2 USB251x Pin Descriptions (continued)
BUFFER
TYPE
I
48 MHz Clock Input Selection
48 MHz external input clock select. When the hub is clocked from an external
clock source, this pin selects either 24 MHz or 48 MHz mode.
‘0’ = 24 MHz
‘1’ = 48 MHz
POWER, GROUND, and NO CONNECTS
CRFILT
VDD Core Regulator Filter Capacitor
This pin must have a 1.0
μF
(or greater) ±20% (ESR <0.1
VSS.
VDD33
PLLFILT
3.3 V Power
PLL Regulator Filter Capacitor
This pin must have a 1.0
μF
(or greater) ±20% (ESR <0.1
VSS.
VSS
Ground Pad / ePad
The package slug is the only VSS for the device and must be tied to ground
with multiple vias.
NC
No Connect
No signal or trace should be routed or attached to these pins.
SYMBOL
SEL48
DESCRIPTION
Ω
) capacitor to
Ω
) capacitor to
5.3
Buffer Type Descriptions
Table 5.3 Buffer Type Descriptions
BUFFER
I
I/O
IPD
IPU
IS
O12
Input.
Input/Output.
Input with internal weak pull-down resistor.
Input with internal weak pull-up resistor.
Input with Schmitt trigger.
Output 12 mA.
DESCRIPTION
SMSC USB251x
27
Revision 1.0 (3-11-09)
DATASHEET
SMSC [ SMSC CORPORATION ]
