Datasheet BA6444FP Datasheet (ROHM)

Motor driver ICs

3-phase motor driver

BA6444FP

The BA6444FP is a 3-phase, full-wave, pseudo-linear motor driver suited for VCR capstan motors. The IC has a torque
ripple cancellation circuit to reduce wow and flutter, and a forced brake circuit that allows abrupt change of operational
mode. The output transistor saturation prevention circuit provides superb torque control over a wide range of current.
FG and hysteresis amplifiers are also built in.

Applications
VCR capstan motors, DAT capstan motors

Features

1) 3-phase, full-wave, pseudo-linear drive system.

2) Torque ripple cancellation circuit.

3) Forced brake circuit.

Absolute maximum ratings (Ta = 25C)

4) Output transistor (high- and low-sides) saturation
prevention circuit.

5) FG and hysteresis amplifiers.

6) Thermal shutdown circuit.

Recommended operating conditions

634

Motor driver ICs BA6444FP

Block diagram

635

Motor driver ICs BA6444FP

Pin descriptions

636

Motor driver ICs BA6444FP

Input/output circuits
(1) I/O circuit interface
Resistances, in Ω, are typical values. Note that the resistance values can vary 30%.

1) ED/S pin (2 pin) 2) BRK pin (3 pin)

3) Motor output (A1: 5 pin, A2: 6 pin,

4) E

C and ECR pins (10 pin, 11 pin)

A3: 9 pin)

5) TL pin (12 pin) 6) Hall signal input pins



: 27 pin, H1: 26 pin, H2: 25 pin,

(H1



: 24 pin, H3: 23 pin, H3: 22 pin)

H2

637

Motor driver ICs BA6444FP

7) Schmitt trigger amplifier I/O pins (17 pin, 16 pin)

8) Amplifier I/O pins (20 pin, 19 pin, 18 pin)

638

Motor driver ICs BA6444FP

Electrical characteristics (unless otherwise noted, Ta = 25C, VCC = 5V, VM = 12V)

639

Motor driver ICs BA6444FP

Circuit 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 ob­tained by superimposing a triangular wave on the trape­zoidal 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 output current is sensed by applying the voltage de­veloped 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

MAX.) under this condition is given by:

(I

TL(TLRNF offset)

V

IMAX. =

where R

RNF is the value of the resistor connected be-

tween the R

RRNF

NF and ground pins and VTL is the voltage ap-

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  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 characteris­tic range provides good control over a wide range of cur­rent and good torque characteristics even during over­loading.

The pins are the inputs to a differential amplifier . A refer­ence 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
The R

NF pin (pin 7) is the ground pin for the output stage.

To sense the output current, a resistor (0.5Ω recom­mended) is connected between pin 7 and the ground.

640

Motor driver ICs BA6444FP

(6) Ripple cancellation circuit
The cancellation ratio of the torque ripple cancellation cir­cuit (Fig. 10) can be adjusted by an external resistor con­nected to pin 1. Select a suitable value by taking wow and
flutter into consideration.
The ripple cancellation ratio can be obtained in the fol­lowing manner. With E

)

input of (H1
and the R

, H2), H3)) = (L, L, H) is denoted as V1,

NF value for the Hall input of (H1

C = 2.7V , the RNF value for the Hall

)

, H2), H3))
= (L, M, H) is denoted as V2. The ripple cancellation ratio
is then given by:

V

R

CC =

2*V1

(V

1)V2)/2

100 (%)

(7) Brake pin
The brake pin threshold depends on the chip tempera­ture as shown in Fig. 16. Make sure that your application
will work properly when using the IC at low or high tem­peratures.

641

Motor driver ICs BA6444FP

Application example

642

Motor driver ICs BA6444FP

Operation notes
(1) Thermal shut down circuit
The BA6444FP has a thermal shutdown circuit to protect
the IC. The shutdown temperatures is 175C (typical)
with a hysteresis width of 45C (typical).
When the circuit is activated due to an increased in chip
temperature, the output pins (pins 5, 6 and 9) are set to
the open state. The circuit is functional against excessive
power dissipation, output short-circuiting, and other
irregularities in the output current, but does not work
against overheating caused by high internal currents due
to externally caused IC damage or pin-to-pin short-cir­cuiting.
(2) The brake circuit has temperature-dependent
thresholds as shown in Fig. 16. Make sure that your ap­plication will work properly when using the IC at low or
high temperatures.
(3) Be sure to connect the radiation fin to the ground.

(4) Hall input
The Hall input circuit is described in (6) of “I/O equivalent
circuits.” Hall devices can be connected in either series
or parallel. Be sure to keep the Hall input within the range
of 1.5V to (V

CC  1.5V).

(5) FG amplifier
Note that unpredictable outputs may occur when the FG
amplifier input is outside the recommended range.
(6) ECGND pin (pin 4)
Pin 4, a torque amplifier ground pin, should be connected
to the ground. By connecting this pin to a point close to
the motor ground, you can prevent the effect of GND
common impedance on the current-sensing resistor
(0.5Ω recommended) connected between R

NF (pin 7)

and the motor ground pin.

Electrical characteristic curves

643

Motor driver ICs BA6444FP

External dimensions (Units: mm)

644