BA3430F [ROHM]
Stereo pre-amplifiers with mute detection circuits for car stereos; 立体声前级放大器与汽车音响静音检测电路
| 型号： | BA3430F |
| 厂家： | 
ROHM |
| 描述： | Stereo pre-amplifiers with mute detection circuits for car stereos |
| 文件： | 总14页 (文件大小：249K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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 de-
signed 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-am-
plifier board into the mechanical components of a car stereo.
FAbsolute maximum ratings (Ta = 25_C)
FRecommended operating conditions (Ta = 25_C)
269
Audio ICs
BA3430S / BA3430F / BA3430FS
FBlock diagram
270
Audio ICs
BA3430S / BA3430F / BA3430FS
FPin descriptions
271
Audio ICs
BA3430S / BA3430F / BA3430FS
FElectrical characteristics (unless otherwise noted, Ta = 25_C and VCC = 9V, f = 1kHz, Rg = 680Ω, VO = *10dBV)
272
Audio ICs
BA3430S / BA3430F / BA3430FS
FMeasurement circuit
FAudio signal amplification circuit
(1) Input switch circuit
The electrolytic capacitor between the input pin and
ground is for preventing switch noise. Although it is pos-
sible 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.
This circuit switches between head A and head B as
needed for the auto reverse function.
A10kΩ orlessresistormustbeconnectedtotheinputpin
to limit the input current.
Equivalent circuit schematic
Truth table
273
Audio ICs
BA3430S / BA3430F / BA3430FS
(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 met-
al tape. The equalizer characteristics are switched be-
tweennormal and metal according to the logic of the met-
al switch pin. A 22kΩ or less resistor must be connected
to the input pin to limit the input current. Thecapacitorbe-
tween the input pin and ground is for preventing switch
noise. It can be omitted without causing incorrect song
detection.
Input switch truth table
Equivalent circuit schematic
(3) Mute circuit
Equivalent circuit schematic
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 be-
tween the input pin and ground is for preventing switch
noise. It can be omitted without causing incorrect song
detection,however, itisbesttouseittoensureproperop-
eration of the mute circuit.
Input switch truth table
274
Audio ICs
BA3430S / BA3430F / BA3430FS
FMute 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
Input switch truth table
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 fre-
quency and gain for playback and fast forward.
2) Input low pass filter
(1) Sensitivity switch circuit
High frequency noise increases during fast forward. This
filter reduces high frequency noise. It consists of an inter-
nal30kΩ resistorwhichcombinestheleftandrightequal-
izer output and an external capacitor connected to Pin 5.
This circuit switches the detection frequency and gain for
playback and fast forward.
A10kΩ orlessresistormustbeconnectedtotheinputpin
to limit the input current. The electrolytic capacitor be-
tween the input pin and ground is for preventing incorrect
detection. Without this capacitor, sensitivity switch noise
may cause incorrect detection of songs.
The cutoff frequency of the low pass filter fH is
1
fH =
(Hz)
2 π C 30k//30k
C = External capacitor connected to Pin 5
275
Audio ICs
BA3430S / BA3430F / BA3430FS
(3) Sensitivity switch amplifier
Equivalent circuit schematic
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 equation holds when the input signal is sufficiently
large.
This circuit detects the presence or not of the signal and
outputs a detection signal.
See Fig. 20 for the small signal time τ1.
The circuit consists of two comparators. The first
comparatordetects 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.
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)
If the signal level drops below VCC /30 (VO-P), the first
comparator turns off and the voltage of the time constant
pinrisesduetotheexternaldischargeresistor. 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 fromthearrivalofthesignaltothechangeover
of the mute detection output pin to low is given as follows:
5.4 C
Equivalent circuit schematic
τ 1 =
(S)
I
276
Audio ICs
BA3430S / BA3430F / BA3430FS
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
at VCC /30.
As an example, when VCC = 9V and f = 5kHz, the mute
detection level during playback is obtained as follows:
a. The reference voltage of the comparator circuit is V =
VCC /30 = 0.3V, therefore, the circuit will operate at an AC
input of 0.3/ 2Vrms = *13.5dBV or more.
b. From the above chart, the gain at 5kHz during play-
back is 80dB.
c. Therefore, the output/input level of mute detection is
*13.5 * 80 = *93.5dBV.
277
Audio ICs
BA3430S / BA3430F / BA3430FS
FApplication example
278
Audio ICs
BA3430S / BA3430F / BA3430FS
FOperation notes
(1) Application circuit
(4) Song detection output/input level
The application circuit is an example of a circuit we re-
commend, however, before using it further examination
of characteristics and patent issues is necessary. If any
ofthevaluesoftheexternalconnectionsarechanged, be
sure to take into consideration both the quiescent and
transient characteristics of the IC and external compo-
nents, and also deviations in the characteristics.
(2) Resistor values for switch pins
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 detec-
tion 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 am-
plifier
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.
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 capaci-
tor and resistor values of Pin 4, and the high cutoff fre-
quency can be set with the capacitor connected to Pin 5
and the internal resistor.
(3) Capacitors for switch pins
The capacitors connected to Pins 20 and 23 are for pre-
venting incorrect operation of the mute detection circuit.
Without these capacitors, the switching sound which oc-
curs 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
throughoutthemutedetectiontime. Ifashortmutedetec-
tion time is set and the error can be tolerated, the capaci-
tors can be omitted. The capacitors at Pins 21 and 22 are
forpreventinga“pop”soundintheaudiosignal. Ifthepop
sound is muted at a latter stage, the capacitors can be
omitted. Naturally, the mute detection circuit will still op-
erate correctly if they are omitted.
(6) Song detection time
The song detection time can be set with the capacitor
connectedtoPin2. Ifthetimeistooshort, shortnoisesig-
nals 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 cur-
rent, select a resistor which is 22kΩ or more.
279
Audio ICs
BA3430S / BA3430F / BA3430FS
FThermal 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. VCC), and Fig. 9 shows the allowed power dissipa-
tion vs. ambient temperature (PdMAX. vs. Ta). Allowed
supply voltage vs. ambient temperature (VCCMAX. vs. Ta)
can be obtained from these curves, and the result is
showninFig. 10. RefertoFig. 10tosetthesupplyvoltage
when designing the application.
FElectriclal charecteristics curves
280
Audio ICs
BA3430S / BA3430F / BA3430FS
281
Audio ICs
BA3430S / BA3430F / BA3430FS
FExternal dimensions (Units: mm)
282
相关型号：
©2020 ICPDF网 联系我们和版权申明