640

Motor driver ICs

BA6444FP

FCircuit operation

(1)

Pseudo-linear output and torque ripple cancellation

The IC generates a trapezoidal (pseudo-linear) output

current, whose waveform phase is 30 degrees ahead of

that of the Hall input voltage (Fig. 9).

The trapezoidal waveform of output current would create

intermittence in the magnetic field generated by the

3-phase motor, and would result in an irregular rotation

of the motor. To prevent this, the output waveform is ob-

tained by superimposing a triangular wave on the trape-

zoidal wave (Fig. 10). This process is called torque ripple

cancellation.

(2)

Torque control

The output current can be controlled by adjusting the

voltage applied to the torque control pins.

The pins are the inputs to a differential amplifier. A refer-

ence voltage between 2.3-3.0V (2.5V recommended) is

applied to pin 11.

A brake is applied to the motor when the brake pin (pin 3)

is put to LOW. The brake mode is activated when the

brake pin voltage is 0.7V or less and deactivated when

the voltage is 2.0V or more.

(3)

Output current sensing and torque limitation

To sense the output current, a resistor (0.5

Ω recom-

mended) is connected between pin 7 and the ground.

The output current is sensed by applying the voltage de-

veloped across this resistor to the TL amplifier input as

a feedback.

The output current can be limited by adjusting the voltage

applied to pin 12. The current is limited when pin 12

reaches the same potential as pin 7. The output current

plied to the TL pin.

(4)

Motor direction control (ED / S pin)

The motor mode is:

Forward when the ED / S-pin voltage is less than 0.9V,

Stop when the voltage is between 1.3

X 3.0V,

Reverse when the voltage is above 3.5V.

In the stop mode, high- and low-side output transistors

are turned off, resulting in a high impedance state.

(5)

Output transistor saturation prevention circuit

This circuit monitors the output voltage and maintain the

operation of the output transistors below their saturation

levels. Operating the transistors in the linear characteris-

tic range provides good control over a wide range of cur-

rent and good torque characteristics even during over-

loading.