AK7755EN_16 Datasheet, PDF (105/109 Pages) Asahi Kasei Microsystems – DSP with Mono ADC Stereo CODEC + Mic/Lineout Amp

[AK7755]
■ Peripheral Circuit
1. Ground
AVSS and DVSS must be connected to the same analog ground plane. Decoupling capacitors,
particularly small capacity capacitors, should be connected as close as possible to the AK7755.
2. Reference Voltage
The AVDD voltage controls analog signal range. VCOM is a common voltage of this chip and the
VCOM pin outputs AVDD/2. A 2.2µF ceramic capacitor connected between the VCOM and AVSS pins
eliminates the effects of high frequency noise. The ceramic capacitor should be connected as close as
possible to the VCOM pin. The VCOM pin must not be connected to external circuits. Digital signal
lines, especially clock signal line should be kept away as far as possible from the VCOM pin in order to
avoid unwanted coupling into the AK7755.
3. Analog Input
Analog input signals are applied to the modulator through the input pin of each channel. Input voltage is
±FS = ±(AVDD-AVSS) x 2.2/3.3 for differential pin and FS = (AVDD-AVSS) x 2.2/3.3 for single-end
pin. When AVDD = 3.3V and AVSS=0.0V, the differential input range is ±2.20Vpp (typ) and it is
2.20Vpp (typ) for single-ended input. The digital output code format is 2's complements. DC offset can
be cancelled by an internal HPF.
The AK7755 samples the analog inputs in 3.072MHz at fs = 48kHz. The digital filter removes noise in
the range from 30kHz to 3.042MHz. The AK7755 includes an anti-aliasing filter (RC filter) to attenuate
a noise around the range from 3.042MHz to 3.072MHz witch is not removed by the HPF. An external
Low Pass Filter is not necessary since most of audio signals do not have large noise in the band around
3.072MHz. However, it is recommended to connect a Low Pass Filter before the ADC when a signal
with large out-of-band noises is input.
The analog source voltage to the AK7755 is +3.3V (typ). Voltage of AVDD + 0.3V or more, voltage of
AVSS – 0.3V or less, and current of 10mA or more must not be applied to analog input pins. Excessive
current will damage the internal protection circuit and will cause latch-up, damaging the IC. If the
external analog circuit voltage is ±15V, the analog input pins must be protected from signals which are in
absolute maximum rating level or more.
10k
22μ
68p
Signal
+ ^10k
-
+
10k
10k ^68p
-
+
2.20Vpp
+
INP*
1μ
+
INN*
1μ
2.20Vpp
Figure 87. Input Buffer Circuit Example (Differential Input)
014006643-E-00
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2014/10