ASAHI KASEI
[AK4551]
1. Grounding and Power Supply Decoupling
VDD and VSS are supplied from analog supply and should be separated from system digital supply. Decoupling capacitors
should be as near to the AK4551 as possible, with the small value ceramic capacitor being nearest.
2. Voltage Reference
The input to VDD voltage sets the analog input/output range. A 0.1uF ceramic capacitor and a 10uF electrolytic capacitor
is connected to VDD and VSS pins, normally. VCOM is a signal ground of this chip. An electrolytic less than 4.7uF in
parallel with a 0.1uF ceramic capacitor attached to these pins eliminates the effects of high frequency noise. No load
current may be drawn from VCOM pin. All signals, especially clock, should be kept away from the VDD, VCOM pins in
order to avoid unwanted coupling into the AK4551.
3. Analog Inputs
ADC inputs are single-ended and internally biased to VCOM. The input signal range scales with the supply voltage and
nominally 0.6xVDD Vpp(typ). The ADC output data format 2’s compliment. The output code is 7FFFFH(@20bit) for
input above a positive full scale and 80000H(@20bit) for input below a negative full scale. The ideal code is 00000H
(@20bit) with no input signal.
The AK4551 samples the analog inputs at 64fs. The digital filter rejects noise above the stop band except for multiples of
64fs. A simple RC filter (fc=150kHz) may be used to attenuate any noise around 64fs and most audio signals do not have
significant energy at 64fs.
4. Analog Outputs
The analog outputs are also single-ended and centered around the VCOM voltage. The input signal range scales with the
supply voltage and nominally 0.6xVDD Vpp(typ). The DAC input data format is 2’s compliment. The output voltage is a
positive full scale for 7FFFFH(@20bit) and a negative full scale for 80000H(@20bit). The ideal output is VCOM voltage
for 00000H(@20bit). If the noise generated by the delta-sigma modulator beyond the audio band would be the problem,
the attenuation by external filter is required.
DC offsets on analog outputs are eliminated by AC coupling since DAC outputs have DC offsets of a few mV.
MS0029-E-00
2000/5
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AKM [ ASAHI KASEI MICROSYSTEMS ]
