Datasheet
USB251xB/xBi
DS00001692C-page 14 2010 - 2015 Microchip Technology Inc.
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 19) the strap pins must be pulled either high or low using the values provided in Table 3-3. Each strap
option is dependent on the pin’s buffer type, as outlined in the sections that follow.
SUSP_IND/ I/O Active/Suspend Status LED: indicates USB state of the hub.
Negated = unconfigured; or configured and in USB suspend
Asserted = hub is configured and is active (i.e., not in suspend)
LOCAL_PWR/ Local Power: detects availability of local self-power source.
Low = self/local power source is NOT available (i.e., the hub gets all power from
the upstream USB VBus)
High = self/local power source is available
NON_REM0 Non-Removable 0 Strap Option: when enabled by package and configuration
settings (see Table 5-1 on page 19), this pin will be sampled (in conjunction with
NON_REM[1]) at RESET_N negation to determine if ports [x:1] contain
permanently attached (non-removable) devices:
Note: When implementing an external LED on this pin, the active state is
outlined below and detailed in Section 3.3.1.3, on page 15.
NON_REM[1:0] = 00 : all ports are removable; LED is active high
NON_REM[1:0] = 01 : port 1 is non-removable; LED is active low
NON_REM[1:0] = 10 : ports 1 and 2 are non-removable; LED is active high
NON_REM[1:0] = 11 : (when available) ports 1, 2, and 3 are non-removable; LED
is active low
TEST IPD Test Pin: treat as a no connect pin or connect to ground. No trace or signal should
be routed or attached to this pin.
POWER, GROUND, and NO CONNECTS
CRFILT VDD Core Regulator Filter Capacitor: this pin can have up to a 0.1 F low-ESR
capacitor to VSS, or be left unconnected.
VDD33 3.3 V Power
VDDA33 3.3 V Analog Power
PLLFILT PLL Regulator Filter Capacitor: this pin can have up to a 0.1 F low-ESR capacitor
to VSS, or be left unconnected.
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 all NC pins.
TABLE 3-3: STRAP OPTION SUMMARY
Strap Option Resistor Value Buffer Type Notes
Non-Removable 47 - 100 k I/O
Internal Pull-Down
10 k IPD
• Only applicable to port power pins
• Contains a built-in resistor
LED 47 - 100 k I/O
TABLE 3-2: USB251XB/XBI PIN DESCRIPTIONS (CONTINUED)
Symbol
Buffer
Type
Description