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PDF BA3402 Data sheet ( Hoja de datos )
| Número de pieza | BA3402 | |
| Descripción | Dual Channel Auto Reverse Tape Preamplifier | |
| Fabricantes | ROHM Semiconductor | |
| Logotipo |  |
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Audio ICs
Dual-channel, auto-reverse
tape preamplifier
BA3402
The BA3402 is a dual preamplifier developed for auto-reverse car tape decks. An electronic switch on the chip switches
between the forward and reverse heads, and this has the benefits of greater reliability, easier wiring, lower space require-
ments, and improved assembly efficiency when compared with conventional mechanical switches. The circuit is de-
signed in such a way that coupling capacitors are not required. In addition to reducing the number of external compo-
nents required, this ensures that the head is not magnetized when the power is applied.
FApplications
Car stereos and play-only auto-reverse cassette decks.
FFeatures
1) Low noise (VNIN = 1.2µVrms).
2) High open loop gain (GVO = 85dB).
3) Reliable electronic switch on the chip. Head switch-
ing for both left and right channels is possible with the
addition of one external switch circuit.
4) Input-side virtual-ground design means that input
coupling capacitors are not required.
FBlock diagram
5) Built-in bias circuit reduces attached component re-
quirements.
6) Low “pop” noise during head switching.
7) Emitter-follower output circuit with large drive capac-
ity.
8) Pin layout allows easy PCB design.
9) Compact package allows high PCB wiring density.
226
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Audio ICs
FElectrical characteristics curves
BA3402
FOperation notes
(1) Input-side virtual ground
If coupling capacitors are used to connect the head with
the preamplifier input, the capacitor charging current
flows in the head and can magnetize it. To prevent this,
a virtual ground is used on the input side, and coupling
capacitors are not required, even with a single-rail sup-
ply.
This is the bias pin input and the virtual ground point for
the negative feedback, and the bias for the input transis-
tor is taken from this terminal. The only DC current that
flows in the magnetic head is the base bias current for the
input transistor, which is not enough to magnetize the
head.
If a floating input is not possible due to the construction
of the magnetic head, or wiring considerations, connect
the input via a coupling capacitor and bias the transistor
using a resistor as shown in Fig.15.
This resistor, the capacitance of the capacitor connected
between the control pin and GND, and the 20kΩ pull-
down resistor on the IC determine the switching speed.
Switching speed increases as the value of the capacitor
is reduced. Set the switching speed so that it matches the
timing of the reversing mechanism. Note, that if the
switching speed is too fast, a “pop” noise will be gener-
ated. The circuit in Fig.16 illustrates how to perform chan-
nel switching by connecting the control pin to GND. Note,
that the switching speed from channel 1 to channel 2 and
from channel 2 to channel 1 is different.
(2) Channel switching control
When the control pin is connected to VCC via a resistor,
channels A-1 and B-1 operate, and when it is open cir-
cuit, channels A-2 and B-2 operate. The recommended
value for the resistor is 15kΩ.
(3) Output coupling capacitors
In car stereos, the preamplifier output passes through the
tone control circuits before going to the power amplifier,
so it is possible to eliminate the output coupling capaci-
tors. Coupling capacitors are required when the pream-
plifier output is used directly as the deck output with no
tone control, or when it is connected directly to power am-
plifier.
230
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| Páginas | Total 6 Páginas | |
| PDF Descargar | [ Datasheet BA3402.PDF ] | |
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