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Audio ICs
Stereo pre-amplifiers with mute
detection circuits for car stereos
BA3430S / BA3430F / BA3430FS
The BA3430S, BA3430F, and BA3430FS are stereo pre-amplifiers with mute detection circuits which have been designed for use in car stereos. The analog circuitry including the pre-amplifier and mute detection and the digital circuitry
such as control logic circuits have been combined together on a single chip. This has made it possible to reduce the
interface with the microcontroller to five parallel inputs and outputs, and enables a very compact circuit configuration
around the tape head.
The BA3430S, BA3430F , or BA3430FS makes it possible to easily incorporate an ultra-compact, high-precision pre-amplifier board into the mechanical components of a car stereo.
Absolute maximum ratings (Ta = 25C)
Recommended operating conditions (Ta = 25C)
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Block diagram
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Pin descriptions
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Electrical characteristics (unless otherwise noted, Ta = 25C and VCC = 9V, f = 1kHz, Rg = 680Ω, VO = 10dBV)
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Measurement circuit
Audio signal amplification circuit
(1) Input switch circuit
This circuit switches between head A and head B as
needed for the auto reverse function.
A 10kΩ or less resistor must be connected to the input pin
to limit the input current.
Equivalent circuit schematic
The electrolytic capacitor between the input pin and
ground is for preventing switch noise. Although it is possible to prevent switch noise in the audio output without
this capacitor by using the mute circuit, switch noise in
the mute detection circuit will not be prevented and noise
will be recognized as a song.
Truth table
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(2) Equalizer amplifier and metal switch circuits
The signal input from the magnetic head will be amplified
based on the NAB characteristics for normal tape or metal tape. The equalizer characteristics are switched between normal and metal according to the logic of the metal switch pin. A 22kΩ or less resistor must be connected
Equivalent circuit schematic
to the input pin to limit the input current. The capacitor between the input pin and ground is for preventing switch
noise. It can be omitted without causing incorrect song
detection.
Input switch truth table
(3) Mute circuit
This circuit mutes the output of the equalizer amplifier. A
22kΩ or less resistor must be connected to the input pin
to limit the input current. The electrolytic capacitor between the input pin and ground is for preventing switch
noise. It can be omitted without causing incorrect song
detection, however, it is best to use it to ensure proper operation of the mute circuit.
Input switch truth table
Equivalent circuit schematic
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Mute detection circuit
(1) Mute detection based on noise and music signals
The signals of each block in the mute detection circuit are
shown in the diagram below.
(2) Sensitivity switch amplifier circuit
The noise level and signal frequency of the tape differ
during playback and fast forward. Therefore, this signal
amplifier includes a circuit for switching the detection frequency and gain for playback and fast forward.
(1) Sensitivity switch circuit
This circuit switches the detection frequency and gain for
playback and fast forward.
A 10kΩ or less resistor must be connected to the input pin
to limit the input current. The electrolytic capacitor between the input pin and ground is for preventing incorrect
detection. Without this capacitor, sensitivity switch noise
may cause incorrect detection of songs.
Input switch truth table
2) Input low pass filter
High frequency noise increases during fast forward. This
filter reduces high frequency noise. It consists of an internal 30kΩ resistor which combines the left and right equalizer output and an external capacitor connected to Pin 5.
The cutoff frequency of the low pass filter f
f
H =
2 π C 30k//30k
1
(Hz)
H is
C = External capacitor connected to Pin 5
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(3) Sensitivity switch amplifier
Equivalent circuit schematic
(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 V
CC /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 V
CC - 2.7(V)
the next comparator turns on, changing the mute detection output pin to low.
If the signal level drops below V
CC / 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 V
CC - 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:
5.4 C
1 =
τ
(S)
I
R2 is a resistor inside the IC which is 100Ω during playback and 360Ω during fast forward.
The gain of the amplifier is
G = 20 log
The low cutoff frequency f
L =
f
2 π C (R1 ) R2)
30k ) R1 ) R2
R1 ) R2
L of the amplifier is
1
(dB)
(Hz)
This equation holds when the input signal is sufficiently
large.
See Fig. 20 for the small signal time τ
The time τ
2 from the ceasing of the signal to the change-
1.
over of the mute detection output pin to high is as follows:
CC)2.0
2 = C R In
τ
1/2 V
2.0
(S)
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
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5) Gain settings for the mute detection circuit
The gain settings for the mute detection circuit are shown below. The reference voltage of the comparator circuit is set
CC/30.
at V
As an example, when V
CC = 9V and f = 5kHz, the mute
detection level during playback is obtained as follows:
a. The reference voltage of the comparator circuit is V =
V
CC/30 = 0.3V , therefore, the circuit will operate at an AC
input of 0.3/ 2V
rms = 13.5dBV or more.
b. From the above chart, the gain at 5kHz during playback is 80dB.
c. Therefore, the output/input level of mute detection is
13.5 80 = 93.5dBV.
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Application example
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Operation notes
(1) Application circuit
The application circuit is an example of a circuit we recommend, however, before using it further examination
of characteristics and patent issues is necessary. If any
of the values of the external connections are changed, be
sure to take into consideration both the quiescent and
transient characteristics of the IC and external components, and also deviations in the characteristics.
(2) Resistor values for switch pins
To prevent incorrect operation of the switch pins, use a
3k to 10kΩ resistor at Pins 20 and 23, and a 2k to 22kΩ
resistor at Pins 21 and 22.
(3) Capacitors for switch pins
The capacitors connected to Pins 20 and 23 are for preventing incorrect operation of the mute detection circuit.
Without these capacitors, the switching sound which occurs when the internal switches are switched will cause
the mute detection output pin (Pin 24) to go low even
when there is no signal, and this error will continue
throughout the mute detection time. If a short mute detection time is set and the error can be tolerated, the capacitors can be omitted. The capacitors at Pins 21 and 22 are
for preventing a “pop” sound in the audio signal. If the pop
sound is muted at a latter stage, the capacitors can be
omitted. Naturally, the mute detection circuit will still operate correctly if they are omitted.
(4) Song detection output/input level
The song detection output/input level can be set with the
resistors connected to Pins 3 and 4. Small values for
these resistors will create a large amplifier gain, lowering
the song detection output /input level. The song detection output / input level in the application circuit is
93.5dBV (5kHz) during playback and 81dBV
(10kHz) during fast forward.
(5) Frequency characteristics of sensitivity switch amplifier
The low cutoff frequency during playback can be set with
the capacitor and resistor values of Pin 3. The low cutoff
frequency during fast forward can be set with the capacitor and resistor values of Pin 4, and the high cutoff frequency can be set with the capacitor connected to Pin 5
and the internal resistor.
(6) Song detection time
The song detection time can be set with the capacitor
connected to Pin 2. If the time is too short, short noise signals will also cause the circuit to operate. Set the time as
long as possible.
(7) Mute detection time
The mute detection time is proportional to the product of
the capacitor and resistor between the supply voltage
and Pin 2. Taking into consideration the allowed IC current, select a resistor which is 22kΩ or more.
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Thermal derating curves
As the allowed power dissipation of the BA3430F /
BA3430FS is small (BA3430F = 550mW, BA3430FS =
800mW), high temperature or high current may cause
the allowed power dissipation to be exceeded. Fig. 8
shows the internal power dissipation vs. supply voltage
(Pd vs. V
tion vs. ambient temperature (Pd
supply voltage vs. ambient temperature (V
can be obtained from these curves, and the result is
shown in Fig. 10. Refer to Fig. 10 to set the supply voltage
when designing the application.
CC), and Fig. 9 shows the allowed power dissipa-
MAX. vs. Ta). Allowed
CCMAX. vs. Ta)
Electriclal charecteristics curves
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External dimensions (Units: mm)
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