Optical disc ICs 4-channel BTL driver for CD players BA6798S The BA6798S is a 4-channel H-bridge BTL driver for CD players and actuators. The 5V regulator and internal standard operational amplifier make this IC suited to a broad range of applications. Applications CD players and CD-ROM drives Features 1) 4-channel BTL driver. 2) SDIP M 24-pin package for high package power. Absolute maximum ratings (Ta = 25C) 374 3) Internal thermal shutdown circuit. 4) Driver gain is adjustable with a single attached resistor. 5) Internal 5V regulator. (requires attached PNP transistor) Optical disc ICs BA6798S Block diagram Pin descriptions 375 Optical disc ICs Pin equivalent circuit diagrams Electrical characteristics (unless otherwise noted, Ta = 25C, VCC = 8V, f = 1kHz, RL = 8Ω) 376 BA6798S Optical disc ICs BA6798S Measurement circuit 377 Optical disc ICs Circuit operation (1) Driver Inputs to the IC are the focus tracking error signal from the servo preamplifier and the control signal from the motor. (2) Regulator This is a typical series regulator that generates a reference voltage internally. A PNP low saturation transistor must be connected. 378 BA6798S The input signals, which normally center on 2.5V, are V / I converted by the preamplifier, generating a current corresponding to the input voltage. This current is passed through a resistor and into the internal reference voltage component, the preamplifier output being a signal centering on the internal reference voltage. Both positive and negative phases are created during V / I conversion, generating BTL output via the driver buffer. Optical disc ICs BA6798S Application example Operation notes (1) The BA6798S has an internal thermal shutdown circuit. Output current is muted when the chip temperature exceeds 175C (typically). (2) If the mute pin (pin 6) voltage is opened or lowered below 0.5V, the output current will be muted. Pin 6 should be pulled up above 2.0V during normal use. (3) The bias pin (pin 17) is muted when lowered below 1.4V (typically). Make sure it stays above 1.6V during normal use. (4) Muting occurs during thermal shutdown, mute-on operations or a drop in the bias pin voltage or supply voltage. In each case, only the drivers are muted. During muting, the output pins remain at the internal bias voltage, roughly (VCCVF / 2). (5) The driver circuit shuts down when the supply voltage drops below 4.5V (typically), and starts up again when the voltage rises above 4.7V (typically). (6) Be sure to connect the IC to a 0.1µF bypass capacitor to the power supply, at the base of the IC. (7) The capacitor between regulator output (pin 7) and GND also serves to prevent oscillation of the IC, so select one with good temperature characteristics. 379 Optical disc ICs Electrical characteristic curves 380 BA6798S Optical disc ICs BA6798S External dimensions (Units: mm) 381