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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 processing. 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 compact 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 playback amplifier has a total gain of 1) The low-noise
2) 3) 4) 5) 6) 79dB (Typ.). Designed for VHS-band operation with low external parts count. It has two built-in circuits for Hi-Fi VCR operation. The circuit has been designed to suppress headswitching noise. Built-in EP / SP gain switching function that boosts the playback gain by 5dB. Built-in VCA for easy playback output adjustment. High-output recording amplifier for audio FM recording. 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 recording 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 Power supply voltage Power dissipation BA7746S BA7746FS Symbol VCC Pd Topr Tstg Limits 7.0 10501 8002 - 10 ~ + 70 - 55 ~ + 125 Unit V mW mW C C
Operating temperature Storage temperature
1 When mounted on a 90mm x 50mm x 1.6mm glass epoxy board, reduced by 10.5mW for each increase in Ta of 1C over 25C. 2 When mounted on a 90mm x 50mm x 1.6mm glass epoxy board, reduced by 8mW for each increase in Ta of 1C over 25C. 1
Video ICs
BA7746S / BA7746FS
*Recommended operating conditions (Ta = 25C)
Parameter Operating voltage Symbol VCCS Min. 4.5 Typ. 5.0 Max. 5.5 Unit V
*Block diagram
P/R
REC AGC FILTER
13
12 REC / PB CTRL
REC CURRENT SENSE
14
AGC
11 REC NF
REC
REC OUT
15
10 REC MIX IN
P
MAIN GND
16 PB / REC
9
OVER REC CTRL
PRE AC - FB ch1
17 ch1
8
REC MUTE CTRL
PRE
PRE IN ch1
18
7
VCC
SW
EP
PRE GND
19
6
VCA CTRL (PRE MUTE)
PRE
VCA
PRE IN ch2
20
5
PRE OUT
PRE AC - FB ch2
ch2
21
4
EP / SP CTRL
N.C.
N.C.
22
3 ch2
HSWP IN
REC + B ch2
23 R ch1 TC
2
REC TC
REC + B ch1
24 R
1
VCC REC + B
2
Video ICs
BA7746S / BA7746FS
*Pin descriptions
Pin No. Pin name, function and remarks Voltage Circuit diagram VCC REC + B * Power supply for REC + B. * Connect to VCC (pin 7).
1
VCC
--
2
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
REC: 0.9V PB: 0V
REC 20k
3
HSWP IN * Pulse input for head switching. * ch1: H, ch2: L
--
24k
4
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
--
40k
EP
SP
5
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
REC: 3.6V PB: 1.9V (RL: 1.8k)
6
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
30k
REC: 2.0V PB: 2.0V
580
20k MUTE H
3
Video ICs
Pin No. Pin name, function and remarks Voltage
BA7746S / BA7746FS
Circuit diagram
7
VCC * Power supply for anything other than REC + B.
VCC
--
8
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.
--
30k
MUTE
REC
9
OVER REC CTRL * OVER REC control. * In OVER REC mode, the recording current is set to + 2dB (Typ.). * Do not leave open circuit.
--
30k
OVER NORMAL
10
REC MIX IN * Recording amplifier input.
REC: 2.9V PB: 2.9V
10k
10k
11
REC NF * Recording amplifier feedback. * Connect the GND of a decoupling capacitor to main GND (pin 16) to improve common-mode distortion.
10.2k
REC: 1.4V PB: 0.5V
240
1.04k
12
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.
--
30k
4
Video ICs
Pin No. Pin name, function and remarks Voltage
BA7746S / BA7746FS
Circuit diagram
13
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: 0V PB: 0V
2k 2k
14
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...48.2mAP-P, 15...38.6mAP-P
REC: 0.58V PB: 0V
15
15
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
14
REC: 4.1V PB: 0V
16
MAIN GND * Earth for circuits other than the preamplifier. * Reference potential for the IC
GND
--
17
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
REC: 0V PB: 0.8V
4k 17 13k 18
18
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.).
REC: 0V PB: 0.7V
5
Video ICs
Pin No. Pin name, function and remarks Voltage
BA7746S / BA7746FS
Circuit diagram
19
PRE GND * GND for the HEAD AMP. * Use this terminal for the pin 17 to pin 21 GND connections to improve the noise characteristics. * Connect this pin to the main GND (pin 16).
GND
--
20
PRE IN ch2 * Inputl for the playback amplifier (ch2). 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.).
REC: 0V PB: 0.7V
4k 21 13k 20
21
PRE AC-FB ch2 * AC feedback for the playback amplifier (ch2). * The high-frequency characteristics of the playback amplifier can be adjusted with the R value.
REC: 0V PB: 0.8V
22
N.C. * Unused. * Connect to MAIN GND to improve the interchannel matching.
--
--
23
REC + B ch2 * REC + B (ch2). * Open emitter output circuit. * Turns on and off in accordance with the REC / PB control signal.
REC: 4.1V PB: 0V
24
REC + B ch1 * REC + B (ch1). * Open emitter output circuit. * Turns on and off in accordance with the REC / PB control signal.
REC: 4.1V PB: 0V
The values given above are design values, they are not ratings and are not guaranteed.
6
Video ICs
BA7746S / BA7746FS
characteristics *Electricalmode (pin 12 "H") (unless otherwise noted, Ta = 25C, VCC = 5.0V, and f = 1.7MHz) Recording
Parameter Quiescent current Output current AGC level Output current AGC level Cross modulation distortion 0.4MHz component Cross modulation distortion 0.9MHz component OVER REC holding voltage OVER REC holding voltage Current emphasis OVER REC MUTE holding voltage REC MUTE holding voltage Mute attenuation Symbol Iq
(REC)
Min. -- 44.2 10 -- -- 0.0 3.5 1.4 0.0 3.5 --
Typ. 66 48.2 13 - 50 - 55 -- -- 1.9 -- -- - 50
Max. 90 52.2 -- - 40 - 40 2.2 VCC 2.4 2.2 VCC - 40
Unit mA mAP-P dB dB dB V V dB V V dB
Conditions No signal, pin 1 + pin 7, inflow current 10pin 93.0dBIN, 14pin OUT AGC
IOAR IOAR CMD04 CMD09 V9L V9H IOR.OV V8L V8H IOR.MU
<
0.8dB, 14pin OUT
10pin MIXIN, 14pin OUT (0.4MHz - 1.3MHz) 10pin MIXIN, 14pin OUT (0.9MHz - 1.3MHz) 9pin DC, When NORMAL REC 9pin DC, When OVER REC 10pin 93.0dBIN, 9pin: "H" 8pin DC, When MUTE OFF 8pin DC, When MUTE ON 10pin 93.0dBIN, 8pin: "H"
f = 1.3MHz (87.0dB) + 1.7MHz (95.0dB) (MIX)
Playback mode (pin 12 "L") (unless otherwise noted, Ta = 25C, VCC = 5.0V, and f = 1.5MHz)
Parameter Supply current Voltage gain CH1 Symbol Iq PB GVP1 Min. -- 75 Typ. 19 79 Max. 31 83 Unit mA dB Conditions Inflow current to pin 7 when no signal. 18pin, 20.5dBIN, 5pin OUT, 3pin: "H" 20pin, 20.5dBIN, 5pin OUT, 3pin: "L" 18pin, 20pin, 20.5dB, 5pin OUT 18pin 31.0dB, 20pin 0 IN, 3pin: "H" "L", 5pin OUT 18pin 0, 20pin 31.0dBIN, 3pin: "L" "H", 5pin OUT 18pin 20.5dBIN, 3pin: "H" f = 2.2MHz / 1.0MHz, 5pin OUT 20pin 20.5dB IN, 3pin: "L" f = 2.2MHz / 1.0MHz, 5pin OUT 6pin 3.2V, 5pin OUT 6pin 0.8V, 5pin OUT Pin 18 and 20 IN, pin 5 OUT 3rd-harmonic distortion, when-30dB. Input conversion for pin 18: 0.01 F + 10 at GND Pin 3: "H", pin 5 OUT. Input conversion for pin 20: 0.01F + 10 at GND Pin 3: "L", pin 5 OUT.
Voltage gain CH2
GVP2 GVP
75
79
83
dB
Voltage gain differential
- 2.0
0
2.0
dB
CH1 to CH2 crosstalk
CT12
--
- 45
- 35
dB
CH2 to CH1 crosstalk
CT21
--
- 45
- 35
dB
CH1 frequency characteristic
fP1
0
- 2.4
-5
dB
CH2 frequency characteristic Gain adjustment headroom Gain adjustment headroom Maximum output voltage
fP2 - GVCA
+ GVCA
0 -- 4 2.0
- 2.4 - 50 6 2.6
-5 - 35 -- --
dB dB dB VP-P Vrms Vrms
VOMP
CH1 input conversion noise
VNP1
--
0.4
1.0
CH2 input conversion noise
VNP2
--
0.4
1.0
7
Video ICs
BA7746S / BA7746FS
*Electrical characteristics"L") (unless otherwise noted, Ta = 25C, VCC = 5.0V, and f = 1.5MHz) Playback mode (pin 12
Parameter Head switching voltage Head switching voltage Output DC offset PB holding voltage REC holding voltage Head switch ON resistance SP holding voltage EP holding voltage Gain emphasis EP Symbol VHS2 VHS1 VODC V12L V12H RSWP V4L V4H GVP.EP Min. 0.0 2.8 - 20 0.0 3.5 -- 0.0 3.5 4.0 Typ. -- -- 0 -- -- 5 -- -- 5.0 Max. 2.2 VCC 20 1.0 VCC 10 2.2 VCC 6.0 Unit V V mV V V V V dB Conditions Pin 3 DC when ch2 operating Pin 3 DC when ch1 operating 18, 20pin 0 IN, 3pin "H" "L" 5pin OUT Pin 12 DC for PB mode Pin 12 DC for REC mode Pin 15 ON resistance Pin 4 DC for SP mode Pin 4 DC for EP mode 18, 20pin 20.5dBIN, 4pin: "H", 5pin OUT
*Measurement circuit
1k
PRE IN ch2 100p 12 12 560
0.1
100p 10
0.01
PRE IN ch1 1k 680 560 220p 0.1
CURRENT SENSE 220k 12 0.1
10
0.01
24
23
22 N.C.
21
20
19
18
17
16
15
14
13
R ch1
R PRE ch2 ch2 PRE ch1 P SW AGC TC EP PB / REC
VCA
REC
P/R
1 7pin SHORT
2
3
4 1.8k
5
6
7 0.01
8
9
10 0.01
11
12 0.22 68k
390 0.047
100 0.1 100 20k 5V OVER REC CTRL REC MUTE CTRL
HSWP IN
REC MIX IN
PR / REC CTRL
EP / SP CTRL
PRE OUT
0.01
Fig. 1
8
Video ICs
BA7746S / BA7746FS
*Control/ mode tables (1) REC PB control
Switch between REC and PB using pin 12.
Control pin REC / PB H L Mode REC PB REC AMP ON OFF Function PRE AMP OFF ON REC + B SW ON OFF HEAD SW (P) OFF ON
(2) OVER REC control Control for OVER REC (current emphasis) is done using pin 9. When in OVER REC mode, the gain setting is recording amplifier AGC level + 1.9dB.
Control pin OVER REC H L Mode OVER REC -- Function REC AGC Level 60.0mAP-P 48.2mAP-P
(3) REC MUTE control Control for REC MUTE when recording is done using pin 8.
Control pin REC MUTE H L Mode REC MUTE -- Function REC AMP OFF ON
(4) EP / SP control EP / SP control during playback is done using pin 4. When EP is selected, the gain of the playback amplifier is increased by 5dB over its normal setting.
Control pin EP / SP H L Mode EP SP Function PRE AMP gain Typ. + 5dB Typ.
9
Video ICs
BA7746S / BA7746FS
*Application example
CURRENT SENSE AUDIO HEAD
100p
100p
220k 680 560 12 220p
0.1
560 560 0.01 0.1 24 23 22 N. C. R R PRE ch1 ch2 ch2 21 20 19
560 0.01 0.1 18 17 16 15
14
13
PRE ch1 P SW AGC
TC
EP
PB / REC
VCA REC P/R
1
2
3
4
5
6
7 0.01
8
9
10 0.01
11
12 0.22
1.8k 390
7pin SHORT
100 0.047 0.01 100 0.1
68k
5V EP / SP CTRL PRE OUT
REC MUTE CTRL
OVER REC CTRL
PB / REC CTRL
REC MIX IN
HSWP IN
Fig. 2
10
Video ICs
BA7746S / BA7746FS
*Operation notes (1) preamplifier
The preamplifier in this IC is a high-gain amplifier for FM audio. This amplifier has been carefully designed for stability. However, the design of the PCB greatly effects the stability of the preamplifier. A list of general precautions are given below. Take note when designing the PCB. 1)The oscillation margin is reduced when the input and output patterns are physically close. The input and output wiring should not come out of the same side of tha IC. Good example Bad example
Input Output
RL
PRE GND
IC MAIN GND
Output GND
3)A large GND pattern under the IC has a shielding effect, and reduced the chance of picking up external noise.
IC Output
Input
Bad example
4)When the preamplifier is connected to a capacitive load such as shilded wire, or when the output current is large, the output may oscillate. In this case, connect a resistor to the preamplifier output (approx. 390).
IC BA7746S / FS REC 270mVP-P BH780XK series REC LPF REC LPF MOD
Input
Output
MOD
2)The GND pattern should be connected at one point to the main IC GND (pin 16). In addition, the preamplifier input-side GND and output-side GND should be as close as possible to the main IC GND. Good example
Input Output
PRE 660mVP-P 390 FM BPF DE MOD
HEAD AMP
Hi-Fi AUDIO
Connection example for BA7746S / BA7746FS and BH780XK series.
RL
PRE GND
IC
MAIN GND
Output GND
11
Video ICs
BA7746S / BA7746FS
(2) REC amplifier The REC amplifier in this IC is for FM audio. Take note of the following points in order to maintain its commonmode distortion characteristics. 1)Connect the REC AGC FILTER (pin 13) and CURRENT SENSE (pin 14) to the main GND of the IC (pin 16) using leads that are as short as possible.
2)REC NF (pin 11) should be as close to the main IC GND as possible. 3)If you connect a resistor to pin 23 or between pins 24 and 15 to monitor the recording current, the resulting voltage drop may cause the IC to function incorrectly. Use the current sense pin (pin 14) to monitor the recording current.
*External dimensions (Units: mm)
BA7746S BA7746FS
22.9 0.3 24 13 6.5 0.3 7.8 0.3 5.4 0.2 24
10.0 0.2 13
0.51Min.
3.4 0.2 3.95 0.3
7.62 1.8 0.1
1
0.3 0.1
12
0.11
0.8
0.36 0.1
0.3Min. 0.15
1.778
0.5 0.1
0 ~ 15
SDIP24
SSOP-A24
12
0.15 0.1
1
12

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