BA6871 Rohm, BA6871 Datasheet - Page 7

• Manufacturer Part Number: BA6871
• Description: 3-phase motor driver
• Manufacturer: Rohm

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. 8).
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. 9). This process is called torque ripple
cancellation.
(2)
The output current can be controlled by adjusting the
voltage applied to the torque control pins (pins 10 and
11).
Motor driver ICs
Pseudo-linear output and torque ripple cancellation
Torque control and reversal brake
These pins are the inputs to a differential amplifier. A ref-
erence voltage between 2.3 X 3.0V (2.5V recommended)
is applied to pin 10.
A brake is applied to the motor as described in the follow-
ing. When the motor is running, pin 11 is given a negative
potential with respect to the reference potential. If the pin
11 potential becomes positive, the IC detects the rise of
pin 11 potential above the reference potential and acti-
vates the motor direction detecting circuit.
The motor direction detecting circuit sends a signal to the
motor direction setting circuit to reverse the motor direc-
tion. This causes a braking torque that depends on the
pin 11 potential, so that the motor quickly reduces its
speed. At the same time, the positive pin 11 potential is
shifted to the reference potential, so that the motor stops
smoothly.
(3)
Pin 31 is the ground pin for the output stage. To sense the
output current, a resistor (0.5
nected between pin 31 and the ground. The output cur-
rent is sensed by applying the voltage developed across
this resistor to pin 13 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 13. The output current
(I
where R
pin 31 and the ground, V
12, and (TL*CS
pins.
MAX.
I
MAX.
) under this condition is given by:
Output current sensing and torque limitation
=
31P
is the value of the resistor connected between
V
12P
*(TL*CS
ofs
R
) is the offset between the TL and CS
31P
12P
ofs
is the voltage applied to pin
)
recommended) is con-
BA6871BS
679