Optical disc ICs PWM driver for CD and MD players BH6505K The BH6505K is a 4-channel PWM driver designed for CD and MD player motor and actuator drives. The power MOSFET output stage allows for applications with low power consumption. This IC also has a charge pump circuit and standard operational amplifier (needed for power MOSFET gate drives), and so supports a wide spectrum of applications. Applications Portable CD players, MD players Features 1) Low power consumption. 2) A minimum of attached components. 3) Good gain precision because of the voltage feedback circuit. 4) Internal mute function for channels 1 and 2. 5) Allows for free-running and clock synchronization operation. 6) Internal standard operational amplifier. 7) Internal charge pump circuit for gate drive. Absolute maximum ratings (Ta = 25C) Recommended operating conditions 241 Optical disc ICs Block diagram 242 BH6505K Optical disc ICs BH6505K Pin descriptions 243 Optical disc ICs Input / output circuits 244 BH6505K Optical disc ICs BH6505K 245 Optical disc ICs 246 BH6505K Optical disc ICs BH6505K 247 Optical disc ICs BH6505K Electrical characteristics (unless otherwise noted, Ta = 25C, BATTERY = 2.4V, Pre.VCC = 3.0V, VC = 1.5V, fCLK = 176.4kHz, RL = 8Ω–47µH) 248 Optical disc ICs BH6505K Measurement circuit 249 Optical disc ICs BH6505K FCircuit operation (1) PWM driver This is an H bridge driver with four N-type FETs in the output stage. Output polarity and PWM duty vary in proportion to the input differential voltage between VC, and to the absolute value. The load is direct-PWM-driven by the square wave with this varying duty. This is a voltage feedback driver and so delivers a constant gain regardless of battery voltage variation. (2) DC / DC converter The DC / DC converter that generates the voltage needed to drive the FETs of the output-stage H bridge. Pre.VCC is raised to 6.5V by attaching an inductance, Schottky barrier diode, and capacitor. (3) Triangular wave generator (1) Freerunning The free-running oscillation frequency of the triangular waves can be set with an attached resistor (Rt, between pin 16 and the ground) and capacitor (Ct, between pin 15 and the ground). The triangular wave has an amplitude of 3 / 5 Pre.VCC at the top and VF (approximately 0.7V) at the bottom. The ratio between rise time and fall time is 3 : 1. Free-running frequency (ft) is determined with the following equation: ft= 3 4 1 S Ct S Rt 250 (2) Clock synchronization The triangular wave can be synchronized by inputting to the CLK pin (17 pin) a pulse wave equal to 0–Pre.VCC (Vp-p). The following precautions should be kept in mind: S The amplitude of the triangular wave decreases as the clock frequency rises. S The PWM driver is a voltage feedback driver, which should preclude any problems unless the setting is such that the triangular wave has an extremely small amplitude. S As mentioned above, a capacitor and resistor are also required during clock synchronization. 1 VF 3 Pre.VCC 5 FOperation notes Attach a bypass capacitor (roughly 1µF) to the power supply, at the base of the IC. Optical disc ICs BH6505K Application example 251 Optical disc ICs Electrical characteristic curves External dimensions (Units: mm) 252 BH6505K