ASAHI KASEI
[AK4564]
n
MIC BLOCK
1. Pre- Amp
Pre-Amp includes selector, Internal MIC or External MIC Mode can be selected by INT/EXT bit. The Pre-Amp is
non-inverting amplifier and internally biased to VCOM voltage with 100kW (typ.). Gain (1+Rf/Ri) of the Pre-Amp is
adjusted by external resistors and should be a range of +18 ~ +30dB.
An external capacitor is needed to cancel DC gain. The Cut-off frequency is determined by an external resistor (Ri) and
a capacitor (C1).
A capacitor of 100pF (C2) should be connected to prevent oscillation of Pre-Amp.
100pF(C2)
C1
Rf
Ri
+
-
+
INT
EXT
Pre-Amp
Figure 12. Pre•Amp
2. Power Supply for MIC
The Power Supply for microphone device is supplied from MPWR pin. MPWR pin can supply the current up to 3mA.
When the output current is 0mA, the output voltage is typically (MVDD – 1.2) V at MVDD=2.8V and typically
(MVDD – 1.4) V at MVDD=4.5V. When the output current is 3mA, the output voltage is typically (MVDD – 1.5) V at
MVDD=2.8V and typically (MVDD – 1.7) V at MVDD=4.5V. When MIC bit is “0”, the output current is not supplied.
MS0140-E-01
2002/07
- 17 -
AKM [ ASAHI KASEI MICROSYSTEMS ]
