1
Video ICs
VCR Hi-Fi audio signal REC / PB
amplifier
BA7746S / BA7746FS
The BA7746S and BA7746FS contains the recording and playback amplifiers required for Hi-Fi VCR signal process-
ing. The recording system uses a constant-current amplifier with AGC to eliminate the need to adjust the recording
current, and ensure stable operation as the head wears. The IC also features REC MUTE and OVER REC functions.
The playback system has a high-gain preamplifier, a low- offset head switch, VCA, and an EP-gain amplifier.
In addition, all functions operate off a single 5V supply, and a H / L control system eliminates the need for special
power supplies for the recording and playback systems. The IC has low power consumpution, and comes in a com-
pact 32-pin SSOP-A package that requires little area on the PCB. It will improve the reliability and performance of
your designs while reducing external component requirements.
Applications
VCRs
Features
1) The low-noise playback amplifier has a total gain of
79dB (Typ.). Designed for VHS-band operation with
low external parts count. It has two built-in circuits
for Hi-Fi VCR operation.
2) The circuit has been designed to suppress head-
switching noise.
3) Built-in EP / SP gain switching function that boosts
the playback gain by 5dB.
4) Built-in VCA for easy playback output adjustment.
5) High-output recording amplifier for audio FM record-
ing.
6) Constant-current drive povides stable recording
characteristics when the load (head impedance) is
fluctuating.
7) Built-in recording level AGC eliminates the need to
adjust recording current.
8) Built-in low-pass filter limits the input bandwidth of
the recording amplifier.
9) Built-in OVER REC recording current amplifier
function and REC MUTE function that stops record-
ing output.
10) Low power consumption. Operates off a single 5V
power supply.
11) Record / playback switching can be done directly
via the system controller, and consumes littele
power.
12) Possible to construct a high-performance audio
system by pairing this chip with a Hi-Fi-audio signal
processing IC.
Absolute maximum ratings (Ta = 25C)
Parameter
Symbol
Limits
Unit
V
CC
7.0
V
BA7746S
BA7746FS
Pd
1050
1
mW
800
2
mW
Topr
10 ~ + 70
C
Tstg
55 ~ + 125
C
1 When mounted on a 90mm
50mm
1.6mm glass epoxy board, reduced by 10.5mW for each increase in Ta of 1
C over 25
C.
2 When mounted on a 90mm
50mm
1.6mm glass epoxy board, reduced by 8mW for each increase in Ta of 1
C over 25
C.
Power supply voltage
Power
dissipation
Operating temperature
Storage temperature
2
Video ICs
BA7746S / BA7746FS
Recommended operating conditions (Ta = 25C)
Parameter
Symbol
Min.
Typ.
Max.
Unit
V
CCS
4.5
5.0
5.5
V
Operating voltage
Block diagram
23
24
22
21
20
19
18
17
16
15
14
13
1
2
3
4
5
6
8
7
10
11
12
REC
VCA
PRE
PRE
AGC
PB / REC
SW
EP
TC
P
P / R
ch1
ch2
ch2
ch1
RR
N.C.
REC AGC FILTER
REC CURRENT SENSE
REC OUT
MAIN GND
PRE AC FB ch1
PRE IN ch1
PRE GND
PRE IN ch2
PRE AC FB ch2
N.C.
REC + B ch2
REC + B ch1
REC / PB CTRL
REC NF
REC MIX IN
OVER REC CTRL
REC MUTE CTRL
V
CC
VCA CTRL
(PRE MUTE)
PRE OUT
HSWP IN
EP / SP CTRL
REC TC
V
CC
REC + B
9
3
Video ICs
BA7746S / BA7746FS
Pin descriptions
1
2
REC: 0.9V
PB: 0V
3
--
4
--
5
REC: 3.6V
PB: 1.9V
6
REC: 2.0V
PB: 2.0V
V
CC
--
(RL: 1.8k
)
Pin No.
Circuit diagram
Pin name, function and remarks
Voltage
V
CC
REC + B
Power supply for REC + B.
Connect to V
CC
(pin 7).
REC TC
REC + B time constant.
Use to adjust the REC + B rise time using the C
value. The value of the built-in resistor is 20k
.
The effect of current spikes when recording is
started is reduced
HSWP IN
Pulse input for head switching.
ch1: H, ch2: L
EP / SP CTRL
EP / SP mode control.
In EP mode, the playback amplifier gain is set to
+ 5dB (Typ.).
EP: H, SP: L
Do not leave open circuit
PRE OUT
Playback amplifier output.
Open emitter output.
When there is a chance of oscillation due to
capacitive load, reduce the output current, or
connect a resistor in series (approx. 390
).
Avoid capacitive coupling with the playback input
VCA CTRL (PRE MUTE)
VCA control.
When the terminal is open (a C is required), the
playback amplifier gain is set to the Typ. value.
The PRE MUTE function is made possible by
connection of a mute H signal to this
through a diode
20k
REC
24k
EP
SP
40k
MUTE H
580
30k
20k
4
Video ICs
BA7746S / BA7746FS
7
V
CC
--
8
--
9
--
10
REC: 2.9V
PB: 2.9V
11
REC: 1.4V
PB: 0.5V
12
--
Pin No.
Pin name, function and remarks
Voltage
Circuit diagram
V
CC
Power supply for anything other than REC + B.
REC MUTE CTRL
REC MUTE control.
In REC MUTE mode, the recording amplifier
output is stopped.
REC: L, REC MUTE: H.
Do not leave open circuit.
OVER REC CTRL
OVER REC control.
In OVER REC mode, the recording current is set
to + 2dB (Typ.).
Do not leave open circuit.
REC MIX IN
Recording amplifier input.
REC NF
Recording amplifier feedback.
Connect the GND of a decoupling capacitor to
main GND (pin 16) to improve common-mode
distortion.
REC / PB CTRL
REC / PB control pin.
Use of an RC circuit time constant to slow the rise
of the control signal reduces noise spikes during
switching.
Do not leave open circuit.
MUTE
REC
30k
OVER NORMAL
30k
10k
10k
10.2k
240
1.04k
30k
5
Video ICs
BA7746S / BA7746FS
13
REC: 0V
PB: 0V
14
REC: 0.58V
PB: 0V
15
REC: 4.1V
PB: 0V
16
GND
--
17
REC: 0V
PB: 0.8V
18
REC: 0V
PB: 0.7V
Pin No.
Pin name, function and remarks
Voltage
Circuit diagram
REC AGC FILTER
REC AGC filter.
The attack characteristics of the recording amplifier
can be adjusted using the CR circuit.
Reduce the CR circuit GND-side impedance to
improve the common-mode distortion.
REC CURRENT SENSE
Terminal for monitoring the recording current.
Open emitter output.
The REC AGC output current can be adjusted with
the R value.
e.g. 12
...
48.2mA
P-P
, 15
...
38.6mA
P-P
REC OUT
Recording amplifier output and head switch.
Open collector output.
The head switch turns on and off in accordance with
the REC / PB control signal
MAIN GND
Earth for circuits other than the preamplifier.
Reference potential for the IC
PRE AC-FB ch1
AC feedback terminal for the playback amplifier
(ch1).
The high-frequency characteristics of the playback
amplifier can be adjusted with the R value
PRE IN ch1
Input terminal for the playback amplifier (ch1).
The low-frequency cutoff characteristics can be
adjusted with the value of the input coupling
capacitor.
The frequency characteristics can be adjusted so
that it is flat with the L value of the rotary
transformer, and the external capacitor C (100pF
etc.).
2k
2k
14
15
17
18
4k
13k
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