Audio ICs
2-channel head switch for radio
cassette recorders
BA3126F / BA3126N
The BA3126F and BA3126N are dual-channel tape head switching ICs designed for use in radio cassette players.
These ICs are designed to withstand voltages of up to 120V
P-P
Min., and can handle large-amplitude bias signals during
recording. Both devices have two channels, and are ideal for use in radio-cassette players.
The package types are 14-pin SOP for the BA3126F, and 9-pin SIP for the BA3126N.
FApplications
Radio-cassette players
FFeatures
1) High withstanding voltage
(120V
P-P
Min. at f = 100kHz).
2) Low “on” resistance (P / B SW : 8Ω,
REC SW : 5Ω)
3) Low offset voltage (P / B SW : 5.0mV,
REC SW : 0.6mV)
FAbsolute
maximum ratings (Ta = 25_C)
FRecommended
operating conditions (Ta = 25_C)
818
Audio ICs
FCircuit
operation
(1) Playback mode
When the control pin voltage goes below 0.5V, the REC
SW goes off and the P / B SW goes on to put the IC into
playback mode. In this mode, the playback signal from
the head is sent to the P / B amplifier via the REC SW.
FOperation
notes
(1) When the voltage on the control pin drops below
0.5V, (pin 5 for the BA3126F, and pin 4 for the BA3126N)
the IC switches to P / B mode . When the voltage is 0V,
the maximum source current generated is 120µA (I
LOW
).
When the voltage on the control pin goes above 3.9V the
IC switches to REC mode. When the voltage is 5V, the
maximum sink current generated is 180µA (I
HIGH
). When
the control pin is open, the voltage on it is 3V
F
(approxi-
mately 2.0V). All switches are on at this time.
BA3126F / BA3126N
(2) REC mode
When the control pin voltage goes above 3.9V, the P / B
SW goes off and the REC SW goes on to put the IC into
record mode. In this mode, the recording signal from
REC amplifier is transmitted to the head via the P / B
SW.
(2) P / B switch (BA3126F : pins 3 and 12, BA3126N
: pins 3 and 7)
This switch is on during playback. Due to the characteris-
tics of the transistor switch, the following DC voltage is
generated :
V
OFSP
< 15mV (V
CC
= 9.0V, V
cont
= 0V)
This switch is off during recording. A built-in, high-with-
standing voltage switch means that it can handle the
large-amplitude bias signal generated by the bias gener-
ator.
Due to variations between individual ICs, we recommend
that you keep the voltage below 120V
P-P
(at f = 100kHz).
(3) REC switch (BA3126F : pins 1 and 14, BA3126N :
pins 1 and 9)
This switch is on during recording. Due to the character-
istics of the transistor switch, the following DC voltage is
generated :
V
OFSP
< 6mV (V
CC
= 9.0V, V
cont
= 5V)
The switch is off during playback, and the playback signal
from the head is transmitted to the playback amplifier.
(4) Recommended operating power supply voltage
range
Operation of the basic functions of the application exam-
ple circuit are guaranteed if operated within the stipulated
power supply voltage and ambient temperature ranges.
We cannot guarantee the ratings for the electrical char-
acteristics, but they will not change radically if the circuit
is operated within the stipulated power supply voltage
and ambient temperature ranges.
(5) Transient characteristics during power supply
switching
When the power is switched on and of in P / B mode
(control pin low), a transient current may flow from the
P / B SW to the REC SW.
If the head is in contact with the tape, and this current
flows into the head, the frequency component will be re-
corded as a pop sound on the tape. Pay due consider-
ation to the power supply on / off timing and the head
position relationship.
(6) Playback-to-recording switching timing
If a large-amplitude signal from the bias oscillator is ap-
plied when the P / B SW is on, the P / B switch may latch
if there is excessive current from the bias oscillator. If this
happens, the P / B SW will not switch off when the con-
trol pin is driven high, and the IC will not enter REC mode.
Design the timing so that when the IC is switched from
playback to recording mode, the P / B SW goes off be-
fore the large-amplitude signal from the bias oscillator is
applied to the P / B SW.
822
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