BA6486 データシートの表示（PDF） - ROHM Semiconductor

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BA6486

FDD spindle motor driver

ROHM Semiconductor 

Motor driver ICs

BA6486FS

For noise filtering, a high-pass filter is given by C3 and a

resistor of 1.6kΩ (typical), and a low-pass filter is given

by C4 and a resistor of 200kΩ (typical). The cutoff fre-

quencies of high-pass and low-pass filters (fH and fL, re-

spectively) are given by:

fH=

1

fL=

1

2π 1.6kΩ C3

2π 200kΩ C4

The C3 and C4 capacitances should be set so as to satis-

fy the following relationship:

fHtfFGtfL

where fFG is the FG frequency. Note that the FG amplifier

inputs have a hysteresis.

The speed discriminator divides the reference clock and

compares with the reference frequency, and then outputs

an error pulse according to the frequency difference. The

motor rotational speed N is given in the following formula.

N=60 S

fosc

S

1

(1)

n

z

fosc is the reference clock frequency,

n is (speed discriminator count) 2,

z is the FG tooth number.

The discriminator count depends on the speed control

pin voltage.

The integrator flattens out the error pulse of the speed

discriminator and creates a control signal for the motor

drive circuit (Fig. 15).

(3) Index amplifier

The index amplifier is a hysteresis amplifier with a typical

hysteresis width of +18mV and –22mV. The input pin is

not biased internally.

(4) Other circuits

S Start / stop circuit

The start / stop circuit puts the IC to the operating state

when the control pin is LOW, and to the standby state (cir-

cuit current is nearly zero) when the control pin is HIGH.

The Hall device bias switch, which is linked to the

start / stop circuit, is turned off during the standby state,

so that the Hall device current is shut down.

S Thermal shutdown circuit

This circuit shuts down the IC currents when the chip

junction temperature is increased to about 175_C (typi-

cal). The thermal shutdown circuit is deactivated when

the temperature drops to about 155_C (typical).

548

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