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 •Video cassette recorders and tape decks •1)Features High withstanding voltage ( ± 65V DC (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 BA7755AF 1 2 VCC SW 3 4 5 GND CTRL2 CTRL1 CTRL1 8 7 6 N.C. N.C. N.C. 1 2 3 5 4 VCC HEAD GND CTRL2 SWITCH 1 Video ICs BA7755A / BA7755AF •Absolute maximum ratings (Ta = 25°C) Parameter Symbol Limits Unit VCC 15 V Pd 400∗1 Power supply voltage Power dissipation – 10 ~ + 65 °C Tstg – 55 ~ + 125 °C BVCC2 ± 65 V Storage temperature Breakdown voltage of switch (pin 2) mW Topr Operating temperature ∗ Reduced by 4mW for each increase in Ta of 1°C over 25°C. •Recommended operating conditions (Ta = 25°C) Parameter Symbol Min. Typ. Max. Unit VCC 4 9 13 V Operating voltage •Electrical characteristics (unless otherwise noted, Ta = 25°C and V Parameter Min. Typ. Max. = 9V) Conditions Unit Supply current ICC1 — 0 10 µA Pin4 “L” or “OPEN” Pin5 “OPEN” Supply current ICC2 2.4 3.9 5.6 mA Pin 4 “L” or “OPEN” Pin 5 control current: 200µA Switch-on resistance RON — 8.0 15.0 Ω Pin 4 “L” or “OPEN” Pin 5 control current: 200µA Switch leakage current ILOFF — 0 10 µA Pin 4 “H”, or “OPEN”, or “L” Pin 5 “OPEN”, pin 2 applied voltage ± 65V Switch AC breakdown voltage BVAC 120 160 — VP-P f = 70kHz VOS — 4.3 15.0 mV Pin 4 “L” or “OPEN” Pin 5 control current: 200µA CTRL1 SW ON control current ICTRL1 (ON) 50 — — µA CTRL1 SW OFF control current ICTRL1 (OFF) — — 1 µA — VTH1 1.70 2.15 2.60 V — RCTRL2 21.0 31.0 42.0 kΩ — Switch offset voltage CTRL2 threshold voltage CTRL2 input resistance 2 Symbol CC — Video ICs BA7755A / BA7755AF control methods •(1)Switch Control with pins 4 and 5 SW1 BA7755A 1 2 3 4 Head OFF 5 SW2 SW1 5V ON SW2 Between pins 2 and 3 OFF High impedance ON Low impedance OFF High impedance ON High impedance R VCC Rⱌ VCC – 1.4 [V] 200 [µA] –10 [kΩ] When VCC = 9V (approx) R ⱌ 28kΩ Fig. 1 (2) Control with pin 4 only BA7755A 1 2 3 4 Head 5 SW1 Between pins 2 and 3 OFF Low impedance ON High impedance REC / EEE Between pins 2 and 3 EE (L) Low impedance REC (H) High impedance R SW1 5V VCC Fig. 2 (3) When used with the BA7751ALS BA7755A 1 2 3 4 5 Head VCC 17 BA7751ALS 20 REC / EE Fig. 3 3 Video ICs BA7755A / BA7755AF •Application example CTRL VCC EE SP MUTE OFF + + 8 10 12 14 16 + 18 R16 68k EE 4.7µ / 25V 68k MUTE ON R13 EP 4.7µ / 25V REC + C18 6 R8 10k + PB C16 4 C10 1000p + R12 10k 100µ / 16V C7 C6 47µ / 16V 2 5.6 k R10 22k C9 4.7µ / 25V R7 56k C12 33µ / 16V R6 + C15 4.7µ / 25V LINE OUT VCC LINE IN 20 22 24 BIAS BIAS ALC DET. ALC VR. BA7751ALS – 26dB BUFF. SW5 R SW1 SW4 SW2 P PB LINE 40dB REC SW3 SW8 SW7 + 3 4 5 C20 + L1 R19 3.9mH 470 AC BIAS 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. BA7755A 2 23 VR2 PB IN REC OUT 1 21 R15 51k 0.033µ 19 C21 0.047µ 17 R9 1M + 15 C19 2.7k 4.7µ / 25V + + 13 C17 10µ / 16V R14 47k 220 R4 C2 1000p + 11 C14 47µ / 16V C4 0.01µ 9 C13 22µ / 16V R1 47 3 5 7 R2 R3 R5 18k 330k 12k VR1 C8 10k 10µ / 16V 4.7µ / 25V C5 33µ / 16V C1 C3 1000p 1 R / P HEAD Fig.4 •External dimensions (Units: mm) BA7755A BA7755AF 5.0 ± 0.2 5 1.3 0.3 ± 0.1 1 4 1.27 0.15 ± 0.1 0.6 0.8 1.5 ± 0.1 0.6 0.11 2.54 8 4.4 ± 0.2 6.2 ± 0.3 1.2 4.9 ± 0.2 2.4 ± 0.2 5 1 3.5 ± 0.5 9.6 ± 0.5 11.8 ± 0.2 0.4 ± 0.1 0.3Min. 0.15 SIP5 4 SOP8