AK4637 Datasheet, PDF (33/96 Pages) Asahi Kasei Microsystems – 24bit Mono CODEC with MIC - SPK-AMP

[AK4637]
■ EXT Master Mode (PMPLL bit = “0”, M/S bit = “1”)
The AK4637 becomes EXT Master Mode by setting PMPLL bit = “0” and M/S bit = “1”. Master clock can
be input to the internal ADC and DAC directly from the MCKI pin without the internal PLL circuit operation.
The external clock required to operate the AK4637 is MCKI (256fs, 384fs, 512fs or 1024fs). The input
frequency of MCKI is selected by CM1-0 bits (Table 14) and the sampling frequency is selected by FS3-2
bits (Table 15). When the state of AK4637 is ADC power-down or Loopback mode, the output of BICK,
FCK and SDTO pins can be stopped by CKOFF bit. When CKOFF bit = “1”, BICK, FCK and SDTO pins
output “L”. The BICK output frequency is selected between 16fs, 32fs, 64fs, by BCKO bit (Table 17).
Mode CM1 bit CM0 bit
MCKI Input
Frequency
Sampling Frequency
Range
0
0
0
256fs
8kHz ≤ fs ≤ 48kHz
(default)
1
0
1
384fs
8kHz < fs ≤ 48kHz
2
1
0
512fs
8kHz < fs ≤ 48kHz
3
1
1
1024fs
8kHz ≤ fs ≤ 24kHz
Table 14. MCKI Frequency at EXT Master Mode (PMPLL bit = “0”, M/S bit = “1”)
Mode FS3 bit FS2 bit FS1 bit FS0 bit
Sampling Frequency
0
0
0
x
x
8kHz ≤ fs ≤ 12kHz
1
0
1
x
x
12kHz < fs ≤ 24kHz
2
1
0
x
x
24kHz < fs ≤ 48kHz
(default)
Others
Others
N/A
Table 15. Setting of Sampling Frequency (x: Do not care, N/A: Not Available)
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 reduced by using higher frequency of the master clock.
The S/N of the DAC output through SPP/SPN pins is shown in Table 16.
MCKI
S/N (fs=8kHz, 20kHzLPF + A-weighted)
256fs
80dB
384fs
80dB
512fs
93dB
1024fs
96dB
Table 16. Relationship between MCKI and S/N of SPP/SPN pins
AK4637
MCKI
BICK
FCK
256fs, 384fs,
512fs or 1024fs
16fs, 32fs, 64fs
1fs
DSP or P
MCLK
BCLK
FCK
SDTO
SDTI
SDTI
SDTO
Figure 24. EXT Master Mode
Mode
0
1
2
3
BCKO1 bit BCKO0 bit BICK Output Frequency
0
0
16fs
0
1
32fs
1
0
64fs
1
1
N/A
Table 17. BICK Output Frequency at Master Mode
(default)
015010680-E-00
- 33 -
2015/09