adav803ast-reel7 Analog Devices, Inc., adav803ast-reel7 Datasheet - Page 22

• Manufacturer Part Number: adav803ast-reel7
• Description: Audio Codec For Recordable Dvd
• Manufacturer: Analog Devices, Inc.

ADAV803
PLL SECTION
The ADAV803 features a dual PLL configuration to generate
independent system clocks for asynchronous operation.
Figure 37 shows the block diagram of the PLL section. The PLL
generates the internal and system clocks from a 27 MHz clock.
This clock is generated either by a crystal connected between
XIN and XOUT, as shown in Figure 35, or from an external
clock source connected directly to XIN. A 54 MHz clock can
also be used, if the internal clock divider is used.
Both PLLs (PLL1 and PLL2) can be programmed independently
and can accommodate a range of sampling rates (32 kHz
/44.1 kHz/48 kHz) with selectable system clock oversampling
rates of 256 and 384. Higher oversampling rates can also be
selected by enabling the doubling of the sampling rate to give
512 or 768 × f
oversampling ratios of 256 or 384 at double sample rates of
64 kHz /88.2 kHz/96 kHz.
The PLL outputs can be routed internally to act as clock sources
for the other component blocks such as the ADC and DAC. The
outputs of the PLLs are also available on the three SYSCLK pins.
Figure 38 shows how the PLLs can be configured to provide the
sampling clocks.
S
ratios. Note that this option also allows
Figure 35. Crystal Connection
MCLKO
C
MCLKI
XOUT
XIN
XTAL
C
REG 0x74
BIT 5
÷2
REG 0x74
BIT 4
÷2
Figure 37. PLL Section Block Diagram
REG 0x78
REG 0x78
BIT 6
BIT 7
Rev. A | Page 22 of 60
DETECTOR
DETECTOR
AND LOOP
AND LOOP
PHASE
FILTER
PHASE
FILTER
Table 7. PLL Frequency Selection Options
PLL
1
2A
2B
The PLLs require some external components to operate
correctly. These components, shown in Figure 36, form a loop
filter that integrates the current pulses from a charge pump and
produces a voltage that is used to tune the VCO. Good quality
capacitors, such as PPS film, are recommended. Figure 37
shows a block diagram of the PLL section, including the master
clock selection. Figure 38 shows how the clock frequencies at
the clock output pins, SYSCLK1 to SYSCLK3, and the internal
PLL clock values, PLL1 and PLL2, are selected.
The clock nodes, PLL1 and PLL2, can be used as master clocks
for the other blocks in the ADAV803, such as the DAC or ADC.
The PLL has separate supply and ground pins, which should be
as clean as possible to prevent electrical noise from being
converted into clock jitter by coupling onto the loop filter pins.
PLL_LF1
PLL_LF2
32/44.1/48
Sample Rate, f
(kHz)
32/44.1/48
64/88.2/96
64/88.2/96
Same as f
for PLL 2A
÷N
÷N
VCO
VCO
10nF
S
AVDD
selected
SCALER N1
SCALER N2
SCALER N3
OUTPUT
OUTPUT
OUTPUT
Figure 36. PLL Loop Filter
S
PLL1
PLL2
732Ω
1.2µF
Normal f
256/384 × f
256/384 × f
256/512 × f
SYSCLK1
SYSCLK2
SYSCLK3
PLL_LFx
PLL BLOCK
MCLK Selection
S
S
S
S
Double f
512/768 × f
256/384 × f
512/768 × f
256/384 × f
S
S
S
S
S