USB 2.0 Hi-Speed Hub Controller
Datasheet
Table 5.2 USB251x Pin Descriptions (continued)
BUFFER
TYPE
SYMBOL
DESCRIPTION
SEL48
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 Ω) capacitor to
VSS.
VDD33
3.3 V Power
PLLFILT
PLL Regulator Filter Capacitor
This pin must have a 1.0 μF (or greater) ±20% (ESR <0.1 Ω) capacitor to
VSS.
VSS
NC
Ground Pad / ePad
The package slug is the only VSS for the device and must be tied to ground
with multiple vias.
No Connect
No signal or trace should be routed or attached to these pins.
5.3
Buffer Type Descriptions
Table 5.3 Buffer Type Descriptions
DESCRIPTION
BUFFER
I
Input.
Input/Output.
I/O
IPD
IPU
IS
Input with internal weak pull-down resistor.
Input with internal weak pull-up resistor.
Input with Schmitt trigger.
O12
Output 12 mA.
SMSC USB251x
27
Revision 1.0 (3-11-09)
DATASHEET
SMSC [ SMSC CORPORATION ]
