BA6798S

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. FApplications CD players and CD-ROM drives FFeatures 1) 4-channel BTL driver. 2) SDIP M 24-pin package for high package power. 3) Internal thermal shutdown circuit. 4) Driver gain is adjustable with a single attached resistor. 5) Internal 5V regulator. (requires attached PNP transistor) FAbsolute maximum ratings (Ta = 25_C) 374 Optical disc ICs FBlock diagram BA6798S FPin descriptions 375 Optical disc ICs FPin equivalent circuit diagrams BA6798S FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 8V, f = 1kHz, RL = 8Ω) 376 Optical disc ICs FMeasurement circuit BA6798S 377 Optical disc ICs FCircuit operation (1) Driver Inputs to the IC are the focus tracking error signal from the servo preamplifier and the control signal from the motor. 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. (2) Regulator This is a typical series regulator that generates a reference voltage internally. A PNP low saturation transistor must be connected. 378 Optical disc ICs FApplication example BA6798S FOperation notes (1) The BA6798S has an internal thermal shutdown circuit. Output current is muted when the chip temperature exceeds 175_C (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 (VCC*VF / 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 FElectrical characteristic curves BA6798S 380 Optical disc ICs FExternal dimensions (Units: mm) BA6798S 381