AK4951AEN Datasheet, PDF (61/105 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with MIC/HP/SPK-AMP

[AK4951A]
■ Charge Pump Circuit
The internal charge pump circuit generates negative voltage (VEE) from AVDD voltage. The VEE voltage
is used for the headphone amplifier. The charge pump circuit starts operation when PMHPL or PMHPR
bit = “1”. PMVCM bit must be set “1” to power up the charge pump circuit. When the BEEP signal is output
to the stereo headphone amplifier without the system clock, the charge pump circuit can be operated
using the internal oscillator by setting PMOSC bit = “1”. The operating frequency of the internal oscillator
is 2.68MHz (typ) and the power up time of the internal oscillator is 1.1μs (typ).
The power-up time of the charge pump circuit is 12.1ms (max). The headphone amplifier and speaker
amplifier will be powered up after the charge pump circuit is powered up (when PMHPL or PMHPR bit =
“1”). The operating frequency of the charge pump circuit is dependent on the sampling frequency.
■ Headphone Amplifier (HPL/HPR pins)
The positive voltage of the headphone amplifier uses the power supply to the DVDD pin, therefore 150mA
of the maximum power supply capacity is needed. The internal charge pump circuit generates negative
voltage (VEE) from AVDD voltage. The headphone amplifier output is single-ended and centered around
on VSS (0V). Therefore, the capacitor for AC-coupling can be removed. The minimum load resistance is
16.
<External Circuit of Headphone Amplifier>
An oscillation prevention circuit (0.22μF±20% capacitor and 33Ω±20% resistor) should be put because it
has the possibility that Headphone Amplifier oscillates in type of headphone.
DAC
HP-AMP
AK4951
Headphone
0.22μ
16Ω
33Ω
Figure 42. External Circuit of Headphone
When PMHPL, PMHPR bits = “1”, headphone outputs are in normal operation. By setting PMHPL and
PMHPR bits = “0”, the headphone-amps are powered-down completely. At that time, the HPL and HPR
pins go to VSS voltage via the internal pulled-down resistor when HPZ bit = “0”. The pulled-down resistor
is 10 (typ). Crosstalk can be reduced by bringing the HPL and HPR pins to Hi-Z state when it occurs on
the path from speaker output to headphone output by enabling the speaker output in this pulled-down
status of the HPL and HPR pins. The HPL and HPR pins become Hi-Z state by setting HPZ bit to “1” when
PMHPL and PMHPR bit = “0”. The headphone-amps can be powered-up/down regardless the HPZ bit
setting.
The power-up time of the headphone amplifiers is max. 34.2ms (internal oscillator: 66.2ms), and
power-down is executed immediately.
016001936-E-00
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2016/03