ASAHI KASEI
[AK4644]
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 52 shows the cut off frequency and the output
power for various resistor/capacitor combinations. The headphone impedance RL is 16Ω. Output powers are shown at
HVDD = 2.7, 3.0 and 3.3V. The output voltage of headphone is 0.6 x AVDD (Vpp).
When an external resistor R is smaller than 12Ω, put an oscillation prevention circuit (0.22µF±20% capacitor and
10Ω±20% resistor) because it has the possibility that Headphone-Amp oscillates.
HP-AMP
C
R
Headphone
16Ω
AK4644
0.22µ
10Ω
Figure 56. External Circuit Example of Headphone
fc [Hz]
BOOST
=OFF
fc [Hz]
BOOST
=MIN
Output Power [mW]@0dBFS
HPG bit
R [Ω]
C [µF]
HVDD=3.0V HVDD=3.3V HVDD=5V
AVDD=3.0V AVDD=3.3V AVDD=3.3V
fs=44.1kHz
220
100
100
47
100
47
220
100
22
45
100
70
149
50
106
45
100
62
17
43
28
78
19
47
17
43
25
69
0
6.8
16
0
25.3
12.5
6.3
30.6
15.1
7.7
30.6
15.1
7.7
0
1
51
(Note 39)
62
(Note 39)
70
100
1.1
1.3
1.3
10
137
Table 52. External Circuit Example
Note 38. Output power at 16Ω load.
Note 39. Output signal is clipped.
<Headphone-Amp PSRR>
When HVDD is directly supplied from the battery in the mobile phone system, RF noise may influences headphone
output performance. When VBAT bit is set to “1”, HP-Amp PSRR for the noise applied to HVDD is improved. In this
case, HP-Amp common voltage is 0.64 x AVDD (typ). When AVDD is 3.3V, common voltage is 2.1V. Therefore, when
HVDD voltage becomes lower than 4.2V, the output signal will be clipped easily.
VBAT bit
0
1
Common Voltage [V]
0.5 x HVDD
0.64 x AVDD
Table 53. HP-Amp Common Voltage
MS0477-E-01
2006/10
- 60 -
AKM [ ASAHI KASEI MICROSYSTEMS ]
