LAN9252VSLASHML datasheet(37/329 Pages) MICROCHIP

37 / 329 page

 2015 Microchip Technology Inc.

DS00001909A-page 37

LAN9252

6.0

CLOCKS, RESETS, AND POWER MANAGEMENT

6.1

Clocks

The device provides generation of all system clocks as required by the various sub-modules of the device. The clocking

sub-system is comprised of the following:

• Crystal Oscillator

• PHY PLL

6.1.1

CRYSTAL OSCILLATOR

The device requires a fixed-frequency 25 MHz clock source for use by the internal clock oscillator and PLL. This is typ-

ically provided by attaching a 25 MHz crystal to the OSCI and OSCO pins as specified in Section 18.7, "Clock Circuit,"

on page 320. Optionally, this clock can be provided by driving the OSCI input pin with a single-ended 25 MHz clock

source. If a single-ended source is selected, the clock input must run continuously for normal device operation. Power

savings modes allow for the oscillator or external clock input to be halted.

The crystal oscillator can be disabled as describe in Section 6.3.4, "Chip Level Power Management," on page 45.

For system level verification, the crystal oscillator output can be enabled onto the IRQ pin. See Section 8.2.7, "Clock

Output Test Mode," on page 56.

Power for the crystal oscillator is provided by a dedicated regulator or separate input pin. See Section 4.1.2, "1.2 V Crys-

tal Oscillator Regulator," on page 31.

6.1.2

PHY PLL

The PHY module receives the 25 MHz reference clock and, in addition to its internal clock usage, outputs a main system

clock that is used to derive device sub-system clocks.

The PHY PLL can be disabled as describe in Section 6.3.4, "Chip Level Power Management," on page 45. The PHY

PLL will be disabled only when requested and if the PHY ports are in a power down mode.

Power for PHY PLL is provided by an external input pin, usually sourced by the device’s 1.2V core regulator. See Section

4.0, "Power Connections," on page 29.

Note:

Crystal specifications are provided in Table 18-12, “Crystal Specifications,” on page 320.

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