Datasheet BA6855AFM Datasheet (ROHM)

Motor driver ICs

CD-ROM spindle motor driver

BA6855AFM

The BA6855AFM is a CD-ROM motor driver with a built-in motor power supply switching regulator.
The switching regulator allows low-power designs, and reduced thermal dissipation from the IC. It is possible to select
reverse brake and short brake modes.

Applications
CD-ROM, CD-R, CD-RW, DVD-ROM, and DVD-RAM

Features

1) Motor switching regulator on chip.

2) Selectable brake mode via BR pin.

3) FG signal output also possible at power save via
FGS.

Absolute maximum ratings (Ta = 25C)

Recommended operating conditions (Ta = 25C)

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Motor driver ICs BA6855AFM

Block diagram

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Motor driver ICs BA6855AFM

Pin descriptions

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Motor driver ICs BA6855AFM

Electrical characteristics (unless otherwise noted, Ta = 25C, VCC = 5V, VR = 12V, and VM = 12V)

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Motor driver ICs BA6855AFM

Operation notes
(1) FGS
When a high-level voltage is input to FGS, the FG output
is output even when power save is on (PS = low level).
Also, the Hall bias terminal stays in the operating state.

(2) Switching regulator
The BA6855AFM has a switching regulator pin.
The IC has an oscillator circuit, and the output is
compared to the low-level voltage detector output and
output on V

REG.

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Motor driver ICs BA6855AFM

Operating in this way reduces the Collector to Emitter
voltage applied on the drive stage transistor, and serves
to reduce the power consumption.
Of the power consumed by the IC itself, most is con­sumed at the collector and emitter of the output stage
transistor. This power consumption (Pc) increases as the
collector to emitter voltage, and output current increases.
This collector to emitter voltage is the power supply volt­age less the voltage applied to the motor, and as the volt­age applied to the motor decreases with the current, this
amount is unnecessarily applied to the between the col­lector and emitter. Therefore, to effectively use power,
(and to prevent power dissipation from exceeding the
IC’s limits) it is necessary to vary the power supply volt­age in accordance with the output current. In other
words, when the output current is low, the power supply
voltage should be lowered, and when it is high, the power
supply voltage should be increased to prevent more volt­age than necessary from being applied between the col­lector and emitter of the output transistor.

(3) V

M variation

The result of the comparison of the output lower-side re­sidual voltage and the triangular wave is output, and V
is controlled by controlling an externally-connected PNP
transistor to maintain the lower-side residual voltage at
a roughly fixed level.

M

(4) The CS pin
The CS pin (pin 19) controls the lower-side residual volt­age (above) in the increasing direction.
Pull it down with a resistor when the IC heat generation
is low, and the external transistor heat generation is high.
Normally this is open.

(5) The relationship between BR and E

C /ECR

When a high level is applied to the BR pin, the normal

C > ECR relationship reverses (EC > ECR) and the IC en-

E
ters short brake mode.

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Motor driver ICs BA6855AFM

Application example

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Motor driver ICs BA6855AFM

Electrical characteristic curves

External dimensions (Units: mm)

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