Rohm BH6505K Pwm driver for cd and md player Datasheet

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
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Optical disc ICs
Block diagram
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BH6505K
Optical disc ICs
BH6505K
Pin descriptions
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Input / output circuits
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BH6505K
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BH6505K
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BH6505K
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BH6505K
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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)
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Optical disc ICs
BH6505K
Measurement circuit
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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
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(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
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Optical disc ICs
Electrical characteristic curves
External dimensions (Units: mm)
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BH6505K
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