WM8310CGEBSLASHV datasheet(48/291 Pages) WOLFSON

48 / 291 page

WM8310

Pre-Production

PP, May 2012, Rev 3.1

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

XTAL_BKUPE

Selects the RTC and 32.768kHz

oscillator in BACKUP state

0 = RTC unclocked in BACKUP

1 = RTC maintained in BACKUP

(Note that XTAL_ENA must also

be set if the RTC is to be

maintained in BACKUP.)

Table 16 Clocking Control

13.2 CRYSTAL OSCILLATOR

The crystal oscillator generates a 32.768kHz reference clock, which is used to provide reference

clock for the Real Time Clock (RTC) in the WM8310. It may also be used as a reference input to the

FLL, for the purpose of generating other clocks. The oscillator requires an external crystal on the XTI

and XTO pins, as well as two capacitors, connected as shown in Figure 17.

Figure 17 Crystal Oscillator

A suitable crystal oscillator should be selected in accordance with the following requirements:

PARAMETER

MIN

MAX

UNITS

Nominal frequency

32.768

kHz

Series resistance



Maximum driving level

0.5

W

Table 17 Selection of Crystal Oscillator Component

The load capacitors C1 and C2 should be selected according to the recommended load capacitance,

CL of the crystal, which is given by the following equation:

Assuming C1 = C2 and CSTRAY = 2.75pF (typical pad i/o capacitance), then:

C1 = C2 = 2 x (CL - 2.75pF).

For example, if the crystal has a load capacitance CL = 9pF, then C1 = C2 = 12.5pF.

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