AK4645 Datasheet, PDF (62/96 Pages) Asahi Kasei Microsystems – Stereo CODEC with MIC/HP-AMP

ASAHI KASEI
[AK4645]
„ Headphone Output
Power supply voltage for the Headphone-Amp is supplied from the HVDD pin and centered on the HVDD/2 voltage at
VBAT bit = “0”. The load resistance is 16Ω (min). HPG bit selects the output voltage (see Table 54).
When HPM bit = “1”, DAC output signal is output to HPL and HPR pins as (L+R)/2 mono signal.
When HPM3 bit = “1”, the signal selected by MICL3 and MICR3 bits (LIN3/RIN3 inputs or MIC-Amp outputs) to HPL
and HPR pins as (L+R)/2 mono signal.
HPG bit
0
1
Output Voltage [Vpp]
0.6 x AVDD
0.91 x AVDD
Table 54. Headphone-Amp Output Voltage
When the HPMTN bit is “0”, the common voltage of Headphone-Amp falls and the outputs (HPL and HPR pins) go to
“L” (HVSS). When the HPMTN bit is “1”, the common voltage rises to HVDD/2 at VBAT bit = “0”. A capacitor between
the MUTET pin and ground reduces pop noise at power-up. Rise/Fall time constant is in proportional to HVDD voltage
and the capacitor at MUTET pin.
[Example]: A capacitor between the MUTET pin and ground = 1.0µF, HVDD=3.3V:
Rise/fall time constant: τ = 100ms(typ), 250ms(max)
Time until the common goes to HVSS when HPMTN bit = “1” Æ “0”: 500ms(max)
When PMHPL and PMHPR bits are “0”, the Headphone-Amp is powered-down, and the outputs (HPL and HPR pins) go
to “L” (HVSS).
PMHPL bit,
PMHPR bit
HPMTN bit
HPL pin,
HPR pin
(1) (2)
(3)
(4)
Figure 56. Power-up/Power-down Timing for Headphone-Amp
(1) Headphone-Amp power-up (PMHPL, PMHPR bit = “1”). The outputs are still HVSS.
(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 HVSS. If the power supply is switched
off or Headphone-Amp is powered-down before the common voltage goes to HVSS, some POP noise occurs.
<External Circuit of Headphone-Amp >
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 55 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 = 3.0, 3.3 and 5.0V. The output voltage of headphone is 0.6 x AVDD (Vpp) @HPG bit = “0” and 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 it has the possibility that Headphone-Amp oscillates.
MS0543-E-00
- 62 -
2006/09