AK4691 Datasheet, PDF (56/80 Pages) Asahi Kasei Microsystems – 4ch ADC + 2ch DAC with MIC/HP/SPK-AMP

[AK4691]
PMHPL bit,
PMHPR bit
HPMTN bit
HPL pin,
HPR pin
(1) (2)
(3)
(4)
Figure 37. Power-up/Power-down Timing for Headphone-Amp
(1) Headphone-Amp power-up (PMHPL, PMHPR bit = “1”). The outputs are still VSS4.
(2) Headphone-Amp common voltage rises up (HPMTN bit = “1”). Common voltage of Headphone-Amp is rising.
(3) Headphone-Amp common voltage falls down (HPMTN bit = “0”). Common voltage of Headphone-Amp is falling.
(4) Headphone-Amp power-down (PMHPL, PMHPR bit = “0”). The outputs are VSS4. If the power supply is switched
off or Headphone-Amp is powered-down before the common voltage settles to VSS4, some POP noise occurs.
When BOOST=OFF, the cut-off frequency (fc) of Headphone-Amp depends on the external resistor and capacitor. This
fc can be shifted to lower frequency by using bass boost function. Table 51 shows the cut off frequency and the output
power for various resistor/capacitor combinations. The headphone impedance R_L is 16Ω. Output powers are shown at
AVDD = LVDD = 2.7, 3.0 and 3.3V. The output voltage of headphone is 0.6 x AVDD (Vpp)@HPG bit = “0”, 0.91 x
AVDD(Vpp)@HPG bit = “1”.
When an external resistor R is smaller than 12Ω, put an oscillation prevention circuit (0.22μF±20% capacitor and
10Ω±20% resistor) because there is a possibility that Headphone-Amp oscillates.
HP-AMP
AK4691
R
0.22μ
10Ω
C _Headphone
16Ω
HPG bit R [Ω]
6.8
0
16
0
1
100
Figure 38. External Circuit Example of Headphone
C [μF]
100
47
100
47
220
100
22
10
fc [Hz]
fc [Hz]
BOOST=OFF BOOST=MIN
@fs=44.1kHz
70
28
149
78
50
19
106
47
45
17
100
43
62
25
137
69
Table 51. External Circuit Example
Output Power [mW]@0dBFS
2.7V
3.0V
3.3V
10.1
12.5
15.1
5.1
6.3
7.7
33
41
50
0.9
1.1
1.3
MS0672-E-00
- 56 -
2007/11