Datasheet BH6505K Datasheet (ROHM)

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.

Absolute 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.

Recommended operating conditions

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Optical disc ICs BH6505K

Block diagram

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Optical disc ICs BH6505K

Pin descriptions

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Optical disc ICs BH6505K

Input / output circuits

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Optical disc ICs BH6505K

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Optical disc ICs BH6505K

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Optical disc ICs BH6505K

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Optical disc ICs BH6505K

Electrical characteristics (unless otherwise noted, Ta = 25C, BATTERY = 2.4V, Pre.VCC = 3.0V, VC = 1.5V,

f

CLK = 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 FET s in the out­put stage. Output polarity and PWM duty vary in propor­tion to the input differential voltage between V

C, 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 FET s of the output-stage H bridge. Pre.V
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:

(2) Clock synchronization

The triangular wave can be synchronized by inputting to
the CLK pin (17 pin) a pulse wave equal to 0–Pre.V
(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

CC

required during clock synchronization.

CC

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ft=

3
4

S

Ct S Rt 1



1

F

V

3
5

Pre.V

CC

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 BH6505K

Electrical characteristic curves

External dimensions (Units: mm)

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