[AK4685]
1. Grounding and Power Supply Decoupling
The AK4685 requires careful attention to power supply and grounding arrangements. AVDD1, AVDD2, AVDD3,
DVDD1, DVDD2, DVDD3, TVDD and PVDD are usually supplied from analog supply in system. VSS1-7 of the
AK4685 must be connected to analog ground plane. System analog ground and digital ground must be connected
separately near to where the supplies are brought onto the printed circuit board. Decoupling capacitors should be as near
to the AK4685 as possible, with the small value ceramic capacitor being the nearest.
2. Voltage Reference Inputs
The voltage of AVDD1 sets the ADC input range, AVDD2(AVDD3) sets the DAC1(DAC2) analog output range.
Normally, 0.1µF ceramic capacitors should be connected between AVDD1/2/3 pins and VSS6/2/3 pins. The VCOM pin
is a signal ground of this chip. An electrolytic capacitor 10μF parallel with a 0.1μF ceramic capacitor attached between
these VCOM pins and VSS6 pin eliminates the effects of high frequency noise. No load current may be drawn from these
VCOM pins. All signals, especially clocks, should be kept away from the AVDD1, AVDD2, AVDD3, and VCOM pins in
order to avoid unwanted coupling into the AK4685.
3. Analog Inputs
The AK4685 receives the analog input through the single-ended Pre-amp using external resistors. The input range is
+/-3.3 x AVDD1/5 Vpp (typ. fs=48kHz) at each analog input pins. Each input pins are biased to 0V(typ) internally. The
ADC output data format is 2’s complement. The internal digital HPF removes the DC offset.
The AK4685 samples the analog inputs at 64fs. The digital filter rejects noise above the stop band except for multiples of
64fs. The AK4685 includes an anti-aliasing filter (RC filter) to attenuate a noise around 64fs.
4. Analog Outputs
The DAC1 outputs can be switched between single-ended and differential outputs.
When differential output is selected, the output range is +/-2.56 x (AVDD2)/5 Vpp(typ). The input data format is two’s
complement. The output voltage is positive full scale for 7FFFFFH (@24-bit) and negative full scale for 800000H
(@24-bit). The ideal voltage is 0V for 000000H(@24-bit). The internal switched-capacitor filter (SCF) attenuates the
noise generated by the delta-sigma modulator beyond the audio passband.
When single-ended output is selected, the output range is+/-1.41 x (AVDD2)/5 Vpp(typ) centered around the VCOM
voltage. The internal switched-capacitor filter (SCF) and continuous-time filter (CTF) attenuate the noise generated by
the delta-sigma modulator beyond the audio passband.
The DAC2 outputs are single-ended output and it is for headphones. The output range is+/-1.71 x (AVDD3)/5 Vpp(typ)
centered around the 0V.The input data format is two’s complement. The output voltage is positive full scale for 7FFFFFH
(@24-bit) and negative full scale for 800000H (@24-bit). The ideal voltage is 0V for 000000H(@24-bit). The internal
switched-capacitor filter (SCF) and continuous-time filter (CTF) attenuate the noise generated by the delta-sigma
modulator beyond the audio passband.
DC offsets on the analog outputs should be eliminated by AC coupling since the analog outputs have a DC offset.
5. Attention to the PCB Wiring
Analog input and output pins should be wired as short as possible in order to avoid unwanted coupling into the AK4685.
MS1106-E-00
2009/08
- 49 -
AKM [ ASAHI KASEI MICROSYSTEMS ]
