AK4538 Datasheet, PDF (33/70 Pages) Asahi Kasei Microsystems – 16Bit DS CODEC with MIC/HP/SPK-AMP

ASAHI KASEI
[AK4538]
n Headphone Output
Power supply voltage for the Headphone-amp is supplied from the HVDD pin and centered on the HVDD/2 voltage. The
Headphone output load resistance is min.20Ω. When the HPL and HPR bits are “1”, output signals are muted and the HPL
and HPR pins output HVDD/2 voltage. When the HPL and HPR bits are “0”, the Headphone-amps are in normal
operation. When the PMHPL and PMHPR bits are “0”, the Headphone-amp is powered down and the outputs (HPL and
HPR pins) go to “L” (HVSS). A capacitor between the MUTET pin and ground reduces pop noise at power-up.
[Example] : A capacitor between the MUTET pin and ground = 1.0µF, a capacitor between the HPL (HPR) pin and
Headphone = 47µF
Time constant of rise time: τr = 100ms, Time constant of fall time: τf = 188ms
PMHPL/R bits
HPL/R pins
(1)
τr
τ ₍₂₎
f
Figure 26. Power-up/Power-down Timing for Headphone-amp
Note: The HPL and HPR bits should be kept to “0” during power-up.
(1) PMHPL and PMHPR bits = “1”
Headphone-amp is powered up. Common voltage of Headphone-amp is rising. This rise time depends on the capacitor
value connected with the MUTET pin. The time constant is τr = 100k x C when the capacitor value on MUTET pin is
“C”.
(2) PMHPL and PMHPR bits = “0”
Headphone-amp is powered down. Common voltage is falling. This fall time depends on the internal resistor and the
capacitor value of HPL/R pins. The time constant is τf = 2k x (2 x C) when the capacitor value on HPL(HPR) pin is “C”.
If the power supply is powered off or Headphone-Amp is powered-up again before the common voltage goes to GND,
some POP noise occurs. It takes 5times of τf that the common voltage goes to GND.
The cut-off frequency of Headphone-amp output depends on the external resistor and capacitor used. Table 18 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 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+10Ω) because it has the
possibility that Headphone-amp oscillates.
HP-AMP
R
C _Headphone
AK4538
0.22 µ
16Ω
10Ω
R [Ω]
6.2
16
6.2
16
Figure 27. External Circuit Example of Headphone
C [µF]
47
47
100
100
fc [Hz]
fc [Hz]
BOOST=OFF BOOST=MID
Output Power [mW]
2.7V
3.0V
3.3V
152.5
63
10.0
12.4
15.0
105.8
43
4.8
6.0
7.2
71.2
27
10.0
12.4
15.0
49.7
20
4.8
6.0
7.2
Table 23. External Circuit Example
MS0198-E-01
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