BA6444 ROHM Electronics, BA6444 Datasheet - Page 7

• Manufacturer Part Number: BA6444
• Description: 3-phase Motor Driver
• Manufacturer: ROHM Electronics

FCircuit operation
(1)
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)
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)
The R
To sense the output current, a resistor (0.5
mended) is connected between pin 7 and the ground.
640
Motor driver ICs
Pseudo-linear output and torque ripple cancellation
Torque control
Output current sensing and torque limitation
NF
pin (pin 7) is the ground pin for the output stage.
recom-
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
(I
where R
tween the R
plied to the TL pin.
(4)
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)
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.
MAX.
I
MAX.
) under this condition is given by:
Motor direction control (ED / S pin)
Output transistor saturation prevention circuit
=
RNF
V
TL
NF
is the value of the resistor connected be-
*(TL*R
and ground pins and V
R
RNF
NF
offset)
TL
is the voltage ap-
BA6444FP