AK7750 Datasheet, PDF (74/77 Pages) Asahi Kasei Microsystems – Audio DSP with Built-in Hands-Free Phone Features

[ASAHI KASEI]
[AK7750]
2) Grounding and Power Supply
When designing with the AK7750, AVDD and DVDD are separately decoupled in order to minimize digital
noise. System Analog power supply is fed to AVDD. In general, power supply lines and ground lines are
separately wired for the analog and digital portions, and they are connected together near the power
supplies (terminals) on the printed circuit board. Small ceramic de-coupling capacitors should be connected
as close as possible to the AK7750.
3) Reference Voltage
An input voltage difference between VREFH pin and VREFL pin determines the analog full scale input and
output. Normally, AVDD is connected to VREFH and AVSS to VREF.
In order to eliminate high frequency noise, connect a 10 uF electrolytic capacitor and a 0.1 uF ceramic
capacitor in parallel between VREFH and AVSS . The ceramic capacitor should be connected as close as
possible to this pin. Digital signals, especially clocks should be wired as far as possible from the VREFH
and VREFL pins in order to avoid coupling with the AK7750.
The AK7750 common voltage is output on VCOM. Do not use this VCOM common voltage for connection
with any external circuits. To eliminate high frequency noise, connect a 10-uF electrolytic capacitor and a
0.1 uF ceramic capacitor between VCOM and AVSS. These capacitors should be placed as close as
possible to the VCOM pin.
4) Analog Input
An analog signal is input to the internal modulator through differential input pins for each channel.
The input voltage range is equal to difference in voltage between AIN+ and AIN- (∆VAIN = (AIN+) – (AIN-)),
and equals ±FS = ±(VREFH – VREFL) x 0.4. When VREFH = 3.3 V and VREFL = 0.0 V, input range is
±1.32 V. Output code format is in 2’s complement.
In the AK7750, the analog input is sampled at 3.072 MHz when fs = 48 KHz. A digital filter rejects noise
ranging from 30 KHz to 3.042 MHz. Noise around the 3.072 MHz periphery band is not rejected. As no
audio signals exhibit noise near 3.072 MHz, noise can be sufficiently attenuated using a simple RC filter.
Analog input signal to the AK7750 must be biased as shown in Figure 1
Analog power supply voltage of the AK7750 is + 3.3 V (typ).
Voltages higher than AVDD + 0.3 V & lower than AVSS – 0.3 V and current exceeding 10 mA should not
be applied on the analog input pins (AINL+, AINL-, AINR+, AINR-).
Injection of excessive current may destroy the internal protection circuits and may cause a latch-up that
results in total device destruction.
Therefore if ±15 V power supplies are used in peripheral analog circuits, the analog input pins must be
protected from signals exceeding absolute maximum ratings.
[MS0296-E-00]
74
2005/03