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| Optical disc 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. FApplications CD-ROM, CD-R, CD-RW, DVD-ROM, and DVD-RAM FFeatures 1) Motor switching regulator on chip. 2) Selectable brake mode via BR pin. 3) FG signal output also possible at power save via FGS. FAbsolute maximum ratings (Ta = 25_C) FRecommended operating conditions (Ta = 25_C) 766 Optical disc ICs FBlock diagram BA6855AFM 767 Optical disc ICs FPin descriptions BA6855AFM 768 Optical disc ICs BA6855AFM FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 5V, VR = 12V, and VM = 12V) 769 Optical disc ICs BA6855AFM FOperation 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 VREG. 770 Optical disc 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 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) VM variation The result of the comparison of the output lower-side residual 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. BA6855AFM (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 EC / ECR When a high level is applied to the BR pin, the normal EC > ECR relationship reverses (EC > ECR) and the IC enters short brake mode. 771 Optical disc ICs FApplication example BA6855AFM 772 Optical disc ICs FElectrical characteristic curves BA6855AFM FExternal dimensions (Units: mm) 773 |
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