ASAHI KASEI
[AK5351]
Analog connections
Analog signal is differentially input into the modulator via the AIN+ and the AIN- pins.The input voltage is the
difference between AIN+ and AIN- pins.The full-scale of each pin is ±2.10Vp-p on its reference
voltage(VREF). In case that the positive input is more than its full-scale, the AK5351 outputs positive
7FFFFH(Hex, Full-scale). In case that the negative input is more than its full-scale, the AK5351 outputs
negative 80000H(Hex, Full-scale). Analog inputs of the AK5351 are normally Full-differential inputs, while they
are also acceptable Single-ended inputs. In case of Single-ended inputs, analog signal is input from either
positive or negative input and the other side inputs bias voltage. Figure 7 is a circuit example which analog
input signal is input 4.20Vp-p into AIN- pin and bias voltage into AIN+ pin. The DC offset is removed by the
internal HPF.
AK5351 samples the analog inputs at 3.072MHz with fs=48kHz.The digital filter rejects all noise between
26.5kHz and 3.0455MHz. However, the filter will not reject frequencies right around 3.072MHz ( and multiples
of 3.072MHz). Most audio signals do not have significant noise energy at 3.072MHz. Hence, a simple RC filter
is sufficient to attenuate any noise energy at 3.072MHz.
The reference voltage for A/D converter is supplied from the VREF pin at VA reference. In order to eliminate
the effects of high frequency noise on the VREF pin, a 10uF or less electrolytic capacitor and a 0.1uF ceramic
capacitor should be connected parallel between the VREF and the VA pins. No current should be driven from
the VREF pin.
The AK5351 accepts +5V supply voltage. Any voltage which exceeds the upper limit of (VA+)+0.3V and lower
limit of AGND-0.3V and any current beyond 10mA for the analog input pins(AINL±, AINR±) should be avoided.
Excessive currents to the input pins may damage the device. Hence input pins must be protected from signals
at or beyond these limits.
Use caution specially in case of using ±15V in surrounding analog circuit.
Figure 6 . Full-differential Input Buffer Circuit Example
Figure 7 . Single-ended Input Buffer Circuit Example
0166-E-00
1997/4
- 15 -
AKM [ ASAHI KASEI MICROSYSTEMS ]
