USB2517 datasheet(42/58 Pages) MICROCHIP

42 / 58 page

USB2517/USB2517I

DS00001598B-page 42

 2013-2016 Microchip Technology Inc.

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 ensured 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 500

A of

current from the upstream USB power source.

Assertion of RESET_N (external pin) causes the following:

All downstream ports are disabled, and PRTPWR power to downstream devices is removed.

The PHYs are disabled, and the differential pairs will be in a high-impedance state.

All transactions immediately terminate; no states are saved.

All internal registers return to the default state (in most cases, 00(h)).

The external crystal oscillator is halted.

The PLL is halted.

LED indicators are disabled.

The Hub is “operational” 500

s 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).

FIGURE 7-3:

LED STRAPPING OPTION

HUB

100K

Strap Low

LED

100K

Strap High

LED

USB2517 Datasheet(PDF) 42 Page - Microchip Technology