WM8731 / WM8731L
Production Data
CRYSTAL OSCILLATOR
The WM8731/L includes a crystal oscillator circuit that allows the audio system’s reference clock to be
generated on the device. This is available to the rest of the audio system in buffered form on
CLKOUT. The crystal oscillator is a low radiation type, designed for low EMI. A typical application
circuit is shown in Figure 25.
XTI/MCLK
XTO
Cp
Cp
DGND
DGND
Figure 25 Crystal Oscillator Application Circuit
The WM8731/L crystal oscillator provides an extremely low jitter clock source. Low jitter clocks are a
requirement for high quality audio ADC and DACs, regardless of the converter architecture. The
WM8731/L architecture is less susceptible than most converter techniques but still requires clocks
with less than approximately 1ns of jitter to maintain performance. In applications where there is more
than one source for the master clock, it is recommended that the clock is generated by the WM8731/L
to minimise such problems.
CLOCKOUT
The Core Clock is internally buffered and made available externally to the audio system on the
CLKOUT output pin. CLKOUT provides a replication of the Core Clock, but buffered as suitable for
driving external loads.
There is no phase inversion between XTI/MCLK, the Core Clock and CLOCKOUT but there will
inevitably be some delay. The delay will be dependent on the load that CLOCKOUT drives. Refer to
Electrical Characteristics.
CLKOUT can also be divided by 2 under software control, refer to Table 14. Note that if CLKOUT is
not required then the CLKOUT buffer on the WM8731/L can be safely powered down to conserve
power (see POWER DOWN section). If the system architect has the choice between using FCLKOUT
=
FMCLK or FCLKOUT = FMCLK/2 in the interface, the latter is recommended to conserve power. When the
divide by two is selected CLKOUT changes on the rising edge of MCLK. Please refer to Electrical
Characteristics for timing information.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
0001000
7
CLKODIV2
0
CLKOUT divider select
Sampling
Control
1 = CLOCKOUT is Core Clock
divided by 2
0 = CLOCKOUT is Core Clock
Table 14 Programming CLKOUT
CLKOUT is disabled and set low whenever the device is in reset.
PD, Rev 4.9, October 2012
35
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
