Datasheet

USB 2.0 Hi-Speed 7-Port Hub Controller
Datasheet
Revision 2.8 (09-17-12) 40 SMSC USB2517
DATASHEET
The Amber and Green LED pins are sampled after RESET_N negation, and the logic values are used to configure
the hub if the internal default configuration mode is selected. The implementation shown below (see Figure 7.3)
shows a recommended passive scheme. When a pin is configured with a “Strap High” configuration, the LED
functions with active low signalling, and the PAD will “sink” the current from the external supply. When a pin is
configured with a “Strap Low” configuration, the LED functions with active high signalling, and the PAD will “source”
the current to the external LED.
Figure 7.3 LED Strapping Option
7.6 Reset
There are two different resets that the Hub experiences. One is a hardware reset (either from the internal POR reset
circuit or via the RESET_N pin) and the second is a USB Bus Reset.
7.6.1 Internal POR Hardware Reset
All reset timing parameters are guaranteed by design.
7.6.2 External Hardware RESET_N
A valid hardware reset is defined as assertion of RESET_N for a minimum of 1us after all power supplies are within
operating range. While reset is asserted, the Hub (and its associated external circuitry) consumes less than 500μA
of current from the upstream USB power source.
Assertion of RESET_N (external pin) causes the following:
1. All downstream ports are disabled, and PRTPWR power to downstream devices is removed.
2. The PHYs are disabled, and the differential pairs will be in a high-impedance state.
3. All transactions immediately terminate; no states are saved.
4. All internal registers return to the default state (in most cases, 00(h)).
5. The external crystal oscillator is halted.
6. The PLL is halted.
7. LED indicators are disabled.
The Hub is “operational” 500μs after RESET_N is negated.
Once operational, the Hub immediately reads OEM-specific data from the external EEPROM (if the SMBus option is
not disabled).
HUB
100K
Strap Low
LED
Pin
100K
Strap High
LED
Pin
+V
LED
LED