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[AK4675]
MS0963-E-00
2008/05
- 57 -
ミ
EXT Slave Mode (PMPLL bit = “0”, M/S bit = “0”)
When PMPLL bit is “0”, the AK4675 becomes EXT mode. Master clock is input from the MCKI pin, the internal PLL
circuit is not operated. This mode is compatible with I/F of the normal audio CODEC. The clocks required to operate are
MCKI (256fs, 384fs, 512fs, 768fs or 1024fs), LRCK (fs) and BICK (
≥
32fs). The master clock (MCKI) should be
synchronized with LRCK. The phase between these clocks does not matter. The input frequency of MCKI is selected by
FS1-0 bits (
).
In case that the CODEC is used without Audio I/F (like phone call), the CODEC can be operated by MCKI only. In this
case, BICK and LRCK can be stopped.
Mode
FS3 bit
FS2 bit
FS1 bit
FS0 bit
MCKI Input
Frequency
Sampling Frequency
Range
0
x
0 0 0 256fs 8kHz
∼
48kHz
1
x
0 0 1 1024fs 8kHz
∼
13kHz
4
x
1 0 0 384fs 8kHz
∼
48kHz
5
x
1 0 1 768fs 8kHz
∼
26kHz
6
x
1 1 0 512fs 8kHz
∼
26kHz
7
x
1 1 1 256fs 8kHz
∼
48kHz
(default)
Others Others
N/A
N/A
(N/A: Not available, x: Don’t care)
Table 11. MCKI Frequency at EXT Slave Mode (PMPLL bit = “0”, M/S bit = “0”)
The S/N of the DAC at low sampling frequencies is worse than at high sampling frequencies due to out-of-band noise.
The out-of-band noise can be improved by using higher frequency of the master clock. The S/N of the DAC output
through LOUT/ROUT pins at fs=8kHz is shown in
MCKI
S/N
(fs=8kHz, 20 A-weighted)
256fs 83dB
512fs 93dB
1024fs 93dB
Table 12. Relationship between MCKI and S/N of LOUT1/ROUT1 pins
The external clocks (MCKI, BICK and LRCK) should always be present whenever the ADC or DAC is in operation
(PMADL bit = “1”, PMADR bit = “1”, PMDAL bit = “1” or PMDAR bit = “1”). If these clocks are not provided, the
AK4675 may draw excess current and it is not possible to operate properly because utilizes dynamic refreshed logic
internally. If the external clocks are not present, the ADC and DAC should be in the power-down mode
(PMADL=PMADR=PMDAL=PMDAR bits = “0”).
AK4675
DSP or
μ
P
MCKI
BICK
LRCK
SDTO
SDTI
BCLK
LRCK
SDTI
SDTO
MCKO
1fs
≥
32fs
MCLK
256fs, 384fs, 512fs,
768fs or 1024fs
Figure 42. EXT Slave Mode