BA6855AFM 데이터 시트보기 (PDF) - ROHM Semiconductor

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BA6855AFM

CD-ROM spindle motor driver

ROHM Semiconductor 

Motor driver ICs

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 con-

sumed 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 volt-

age less the voltage applied to the motor, and as the volt-

age applied to the motor decreases with the current, this

amount is unnecessarily applied to the between the col-

lector 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 volt-

age 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 volt-

age than necessary from being applied between the col-

lector and emitter of the output transistor.

(3) VM variation

The result of the comparison of the output lower-side re-

sidual voltage and the triangular wave is output, and VM

is controlled by controlling an externally-connected PNP

transistor to maintain the lower-side residual voltage at

a roughly fixed level.

(4) The CS pin

The CS pin (pin 19) controls the lower-side residual volt-

age (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 EC / ECR

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

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

ters short brake mode.

846

BA6855AFM

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