BA3430F Ver la hoja de datos (PDF) - ROHM Semiconductor
Número de pieza
componentes Descripción
Fabricante
BA3430F Datasheet PDF : 14 Pages
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Audio ICs
(3) Sensitivity switch amplifier
Equivalent circuit schematic
BA3430S / BA3430F / BA3430FS
R2 is a resistor inside the IC which is 100Ω during play-
back and 360Ω during fast forward.
The gain of the amplifier is
30k ) R1 ) R2
G = 20 log
(dB)
R1 ) R2
The low cutoff frequency fL of the amplifier is
1
fL =
(Hz)
2 π C (R1 ) R2)
(4) Comparator circuit
This circuit detects the presence or not of the signal and
outputs a detection signal.
The circuit consists of two comparators. The first
comparator detects the level of the signal and the second
comparator detects the duration of the signal.
When a signal above VCC / 30 (VO-P) is input, the first
comparator turns on and draws a constant current I from
the time constant pin. This causes the voltage of the time
constant pin to fall, and when it drops below VCC - 2.7(V)
the next comparator turns on, changing the mute detec-
tion output pin to low.
If the signal level drops below VCC / 30 (VO-P), the first
comparator turns off and the voltage of the time constant
pin rises due to the external discharge resistor. When this
voltage rises above VCC - 2.0(V), the next comparator
turns off, changing the mute detection output pin to high.
The time ι1 from the arrival of the signal to the changeover
of the mute detection output pin to low is given as follows:
τ1=
5.4 C
(S)
I
This equation holds when the input signal is sufficiently
large.
See Fig. 20 for the small signal time τ1.
The time τ2 from the ceasing of the signal to the change-
over of the mute detection output pin to high is as follows:
1/2 VCC)2.0
τ 2 = C R In
(S)
2.0
I: Output current of first comparator = approx. 1mA
C: External capacitor connected to time constant pin
R: External resistor connected to time constant pin (this
should be 22kΩ or higher)
Equivalent circuit schematic
276
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