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| Video ICs High-voltage audio head selection switch BA7755A / BA7755AF The standard audio circuits of video cassette recorders and the recording circuits of tape decks use AC bias recording to record the audio signal onto the tape. This bias voltage is some tens of volts, and a high-capacity bias-side switch is required to electronically switch the head when in playback or record mode. The BA7755A and BA7755AF are high-voltage switching ICs designed to switch voltages as high as 65VDC or AC120VP-P (f = 70Hz). Two control systems, one for current control, and one for voltage control are provided, so the ICs can be used in circuits that employ either method. By combining the BA7755A or BA7755AF with the BA7751ALS recording / playback amplifier, it is possible to construct a compact recording / playback audio circuit. In addition, the BA7755A and BA7755AF are an excellent choice for a wide variety of other high-voltage switching applications. *Applications recorders and tape decks Video cassette *Features 1) High withstanding voltage ( 65VDC (Min.), AC120VP-P (Min.), f = 70Hz). 2) Circuits for either current control or voltage control are provided on the chip. 3) Compact SIP 5pin or SOP 8pin package. *Block diagram BA7755A 1 VCC 2 SW 3 4 5 GND CTRL2 CTRL1 BA7755AF CTRL1 8 7 6 5 N.C. N.C. N.C. 1 2 3 4 VCC HEAD GND CTRL2 SWITCH 1 Video ICs BA7755A / BA7755AF *Absolute maximum ratings (Ta = 25C) Parameter Power supply voltage Power dissipation Operating temperature Storage temperature Breakdown voltage of switch (pin 2) Symbol VCC Pd Topr Tstg BVCC2 Limits 15 4001 - 10 ~ + 65 - 55 ~ + 125 65 Unit V mW C C V Reduced by 4mW for each increase in Ta of 1C over 25C. *Recommended operating conditions (Ta = 25C) Parameter Operating voltage Symbol VCC Min. 4 Typ. 9 Max. 13 Unit V *Electrical characteristics (unless otherwise noted, Ta = 25C and VCC = 9V) Parameter Supply current Supply current Switch-on resistance Switch leakage current Switch AC breakdown voltage Switch offset voltage CTRL1 SW ON control current CTRL1 SW OFF control current CTRL2 threshold voltage CTRL2 input resistance Symbol ICC1 ICC2 RON ILOFF BVAC VOS ICTRL1 (ON) ICTRL1 (OFF) VTH1 RCTRL2 Min. -- 2.4 -- -- 120 -- 50 -- 1.70 21.0 Typ. 0 3.9 8.0 0 160 4.3 -- -- 2.15 31.0 Max. 10 5.6 15.0 10 -- 15.0 -- 1 2.60 42.0 Unit A mA A VP-P mV A A V k Conditions Pin4 "L" or "OPEN" Pin5 "OPEN" Pin 4 "L" or "OPEN" Pin 5 control current: 200A Pin 4 "L" or "OPEN" Pin 5 control current: 200A Pin 4 "H", or "OPEN", or "L" Pin 5 "OPEN", pin 2 applied voltage 65V f = 70kHz Pin 4 "L" or "OPEN" Pin 5 control current: 200A -- -- -- -- 2 Video ICs BA7755A / BA7755AF *Switch control methods 5 (1) Control with pins 4 and SW1 BA7755A 1 2 3 4 5 SW2 OFF ON OFF ON Between pins 2 and 3 High impedance Low impedance High impedance High impedance OFF Head SW1 5V SW2 ON VCC R R Fig. 1 VCC - 1.4 [V] 200 [A] -10 [k] 28k When VCC = 9V (approx) R (2) Control with pin 4 only SW1 OFF 1 2 3 4 5 BA7755A Between pins 2 and 3 Low impedance High impedance ON R Head SW1 5V VCC Fig. 2 (3) When used with the BA7751ALS BA7755A 1 2 3 4 5 REC / EEE EE (L) REC (H) Between pins 2 and 3 Low impedance High impedance Head VCC 17 BA7751ALS 20 REC / EE Fig. 3 3 Video ICs BA7755A / BA7755AF *Application example VCC LINE IN R10 22k CTRL VCC LINE OUT C15 4.7 / 25V R12 10k PB EE 4.7 / 25V 68k 4.7 / 25V REC EE R16 68k EP SP MUTE ON MUTE OFF R6 + 100 / 16V C7 5.6 k C10 C9 4.7 / 25V R7 56k C12 33 / 16V C6 47 / 16V + 1000p + R8 10k + R13 + + + C16 2 4 6 8 10 BIAS 12 14 16 18 C18 20 22 24 BUFF. BIAS BA7751ALS SW1 ALC DET. ALC VR. R SW2 LINE 40dB SW5 - 26dB SW4 SW3 REC SW8 P PB SW7 C3 1000p 1 4.7 / 25V C5 33 / 16V C1 C17 10 / 16V R14 47k C13 22 / 16V C14 47 / 16V R9 1M VR1 C8 10k 10 / 16V C19 2.7k 4.7 / 25V R1 47 C2 1000p + C4 0.01 220 + + 3.9mH 470 L1 R19 C21 0.047 + + R4 PB IN REC OUT VR2 AC BIAS BA7755A 1 2 3 4 5 R / P HEAD Note: R13, C16, R16 and C18 prevent switching noise. These are not required if external muting or some other method is used to eliminate switching noise. Fig.4 *External dimensions (Units: mm) BA7755A BA7755AF 5.0 0.2 11.8 0.2 4.9 0.2 2.4 0.2 8 6.2 0.3 4.4 0.2 5 9.6 0.5 1.2 0.033 0.15 0.1 3.5 0.5 2.54 0.6 0.6 0.8 1.3 0.3 0.1 1.5 0.1 1 5 1 4 0.11 1.27 0.4 0.1 0.3Min. 0.15 SIP5 SOP8 4 C20 3 5 7 R2 R3 R5 18k 330k 12k 9 11 + 13 15 17 19 21 23 R15 51k |
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