580
Motor driver ICs
2-phase motor driver for VCR cylinder
motors
BA6825FS / BA6826FS
The BA6825FS and BA6826FS are direct-drive motor drivers suitable for 2-phase, full-wave linear motors. They consist
of a Hall amplifier control circuit and driver circuits.
F
Applications
VCR cylinder motors
F
Features
1) Linear drive system provides low switching noise.
2) Constant supply voltage pin for hall devices.
3) High ratio of output current against control current.
(4000 Typ.)
4) Available in compact surface-mount packages.
F
Block diagram
581
Motor driver ICs
BA6825FS / BA6826FS
F
Absolute maximum ratings (Ta = 25
_
C)
F
Recommended operating conditions
F
Electrical characteristics (unless otherwise noted, Ta = 25
_
C, V
CC
= 12V)
F
Pin descriptions
582
Motor driver ICs
BA6825FS / BA6826FS
F
Input / output circuits
(1)
Hall and E
CI
inputs
(2)
Coil output
F
Circuit operation
(1)
The signal from the Hall device is amplified by the
Hall amplifier and then supplied to the driver circuit. The
driver gain, which is constant, is regulated by changing
the Hall amplifier gain with the input current on the output
current control pin (E
CI
pin). The motor rotational speed
is sensed by the FG, and the output of which is F / I-con-
verted and supplied to the E
CI
pin as a feedback signal,
so that a constant rotational speed is maintained as fol-
lows :
(
1) The motor speed decreases.
(
2) The speed control IC outputs a feedback signal to the
ECI pin.
(
3) The Hall amplifier gain increases.
(
4) The output current increases.
(
5) The motor speed increases.
(2)
When the voltage on Hall IN
1
(
)
) is higher than the
voltage on Hall IN
1
(
*
), an output current flows from
OUT1 (
*
) to OUT1 (
)
) according to the voltage differen-
tial. When the voltage on Hall IN
1
(
*
) is higher, on the
other hand, an output current flows from OUT1 (
)
) to
OUT1 (
*
).
Similarly, when the voltage on Hall IN
2
(
)
) is higher than
the voltage on Hall IN
2
(
*
), an output current flows from
OUT2 (
*
) to OUT2 (
)
) according to the voltage differen-
tial. When the voltage on Hall IN
2
(
*
) is higher, on the
other hand, an output current flows from OUT2 (
)
) to
OUT2 (
*
).
583
Motor driver ICs
BA6825FS / BA6826FS
(3)
Output waveforms are shown in Fig. 5. Because of
the amplifier offset, the output is left OPEN when the out-
put signal switches from positive to negative. The output
waveform is determined by the external circuit because
the IC impedance increases during this transition period.
Since inductive loads are usually provided, a capacitor
should be connected to suppress the backlash voltage.
F
Operation notes
(1)
E
CI
input
The ECI input circuit has 2V
F
and a 500
resistor con-
nected in series. Current is limited only by the 500
re-
sistor.
(2)
Hall input
Signals of 50mV (peak to peak) or greater should be ap-
plied to the Hall device input. The DC input range is be-
tween 2V and (Vreg
*
1.5V). There will be no problem if
the input is centered around Vreg / 2.
Because the Hall input impedance is 1M
or grater, any
type of Hall device can be connected. No current flows
when the transistor is off because the Hall input pins (
)
and
*
) are differential.
Because the ICs are linear drivers, any DC offset in the
Hall device will be amplified and appear in the output.
Use Hall devices having a minimum offset. Hall devices
can be connected in either series or parallel.
(3)
Thermal shutdown circuit
The circuit puts the driver outputs (9, 11, 12, and 14 pin)
to the open state at the temperature of 175
_
C (typical).
There is a temperature difference of about 20
_
C between
the temperatures at which the circuit is activated and
deactivated.
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