562

Motor driver ICs

BA6492BFS

(3)

Index signal circuit

The index signal circuit receives and amplifies differential

inputs of Hall device signals. The Hall inputs have a hys-

teresis. The monostable multivibrator devices create a

delay time from the zero-cross point, and outputs a pulse

after the delay time. The delay time and the pulse width

can be set arbitrarily with the time constant of the external

CR. The following equations are given for the delay times

T1, T2, and T3 for the speed control pin voltage levels of

LOW, HIGH, and MEDIUM, respectively:

T1 1.35

C5

VR [sec]

(Typ.)

T2 1.13

C5

VR [sec]

(Typ.)

T3 0.68

C5

VR [sec]

(Typ.)

T4 2.14

C4 [sec]

(Typ.)

T1 / T2 = 1.2

(Typ.)

T1 / T3 = 2.0

(Typ.)

The delay angle remains constant regardless of changes

in the motor speed.

(4)

Other circuits

The start / stop circuit puts the IC to the operational 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 elements bias switch, which is linked to the

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

so that the Hall elements current is shut down.

The thermal shutdown circuit shuts down the IC currents

when the chip junction temperature is increased to about

175

_C (typical). The thermal shutdown circuit is deacti-

vated when the temperature drops to about 20

_C (typi-

cal).