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| Optical disc ICs PWM driver for CD and MD players BH6504K The BH6504K is a 4-channel PWM driver designed for CD and MD player motors and actuator drives. The power MOFSET 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. FApplications Portable CD players, MD players FFeatures 1) Low power consumption. 2) A minimum of attached components. 3) Excellent gain precision because of the voltage feedback circuit. 4) Internal mute function for channel 1. FAbsolute maximum ratings (Ta = 25_C) 5) Allows for free-running and clock synchronization operation. 6) Internal standard operational amplifier. 7) Internal charge pump circuit for gate drive. 8) Switchable to doubled clock synchronization. FRecommended operating conditions 226 Optical disc ICs FBlock diagram BH6504K 227 Optical disc ICs FPin descriptions BH6504K 228 Optical disc ICs FInput / output circuits BH6504K 229 Optical disc ICs BH6504K 230 Optical disc ICs BH6504K 231 Optical disc ICs BH6504K 232 Optical disc ICs BH6504K FElectrical characteristics (unless otherwise noted, Ta = 25_C, Battery = 2.4V, Pre.VCC = 3.0V, VC = 1.5V, fCLK = 176.4kHz, RL = 8-47H) 233 Optical disc ICs FMeasurement circuit BH6504K 234 Optical disc ICs FMeasurement circuit switch tables BH6504K PWM driver DC / DC converter Triangular wave generator Control pin threshold 235 Optical disc ICs Operational amplifier BH6504K 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 convertor 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) Free-running oscillation 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 S 1 Ct S Rt 1* VF 3 Pre.Vcc 5 236 Optical disc ICs (2) Clock synchronization The triangular wave can be synchronized by inputting to the CLK pin (pin17) a pulse wave equal to 0-Pre.VCC (Vpp). The following precautions should be kept in mind: S The amplitude of the triangular wave decreases as the clock frequency rises. BH6504K 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. (3) Using the ESP pin 1. To operate the PWM driver at 176.4kHz 2. To operate the PWM driver at 88.2kHz 237 Optical disc ICs FApplication example BH6504K 238 Optical disc ICs FOperation notes Attach a bypass capacitor (roughly 1F) to the power supply, at the base of the IC. BH6504K FElectrical characteristic curves 239 Optical disc ICs FExternal dimensions (Units: mm) BH6504K 240 |
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