ROHM BA6970FS

Motor driver ICs
2-phase motor driver for VCR cylinder
motors
BA6970FS
The BA6970FS is a direct-drive motor driver suitable for 2-phase, full-wave linear motors. The IC consists of a Hall amplifier control circuit, driver circuits, FG / PG signal amplifiers, and hysteresis amplifiers.
Applications
VCR cylinder motors
Features
1) Linear drive system provides low switching noise.
2) Output current can be controlled by either current or
voltage input.
3) Two amplifiers and two hysteresis amplifiers.
Block diagram
594
4) Constant supply voltage pin for hall devices.
5) High ratio of output current and control current.
(4000 typically)
6) Available in a compact surface-mount package.
Motor driver ICs
BA6970FS
FAbsolute maximum ratings (Ta = 25_C)
FRecommended operating conditions (Ta = 25_C)
595
Motor driver ICs
FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 12V)
596
BA6970FS
Motor driver ICs
BA6970FS
Pin descriptions
597
Motor driver ICs
Input / output circuits
(1) ECV (22 pin)
BA6970FS
(4)
I / O of amplifiers 1 and 2
Fig.1
(2)
Coil output (8, 6, 5, 3 pin)
Fig.4
(5)
I / O of hysteresis amplifiers
Fig.2
(3)
Hall inputs (9, 10, 11, 12 pin), ECI input
Fig.5
∗Note that the resistance values can vary ±30%
Fig.3
598
Motor driver ICs
BA6970FS
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 ECI input current or the ECV
input voltage (ECI and ECV are output current control pins).
The motor rotational speed is sensed by the FG, and the
output from which is F / I-converted and supplied to the
ECI pin or F / V-converted and supplied to the ECV pin as
a feedback signal, so that a constant rotational speed is
maintained as follows (Fig. 6) :
(1) The motor speed decreases.
(2) The speed control IC outputs a feedback signal
(3) The Hall amplifier gain increases.
(4) The output current increases.
(5) The motor speed increases.
(2) When the voltage on Hall INφ1 () is higher than the
voltage on Hall INφ1 (), an output current flows from
OUT1 () to OUT1 () according to the voltage differential. When the voltage on Hall INφ1 () is higher, on the
other hand, an output current flows from OUT1 () to
OUT1 ().
Similarly, when the voltage on Hall INφ2 () is higher than
the voltage on Hall INφ2 (), an output current flows from
OUT2 () to OUT2 () according to the voltage differential. When the voltage on Hall INφ2 () is higher, on the
other hand, an output current flows from OUT2 () to
OUT2 ().
Fig.6
Fig.7
Fig.8
599
Motor driver ICs
BA6970FS
(3) Output waveforms are shown in Fig. 9. Because of
the amplifier offset, the output is left OPEN when the output 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 backlash voltages.
Operation notes
(1) ECV input (pin 22)
The ECV input is plotted against the output current in Fig.
10.
Fig.9
Fig.10
(2) Hall input
Hall input signals of 50mV (peak to peak) or greater
should be applied between pins 9 and 10 and between
pins 11 and 12. The DC input range is 2V to
(Vreg1.5V). There will be no problem if the input is centered around Vreg / 2.
Because the Hall input impedance is 1MΩ or grater, any
type of Hall device can be connected. No current flows
when the transistor is off because pins 9 and 10 as well
as pins 11 and 12 are differential inputs.
Because the IC is a linear driver, 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.
Fig.11
600
Motor driver ICs
BA6970FS
(3) ECI input
The ECI input circuit has 2VF and a 500Ω resistor connected in series. Current is limited only by the 500Ω resistor.
(4) Amplifiers 1 and 2
An input range of 0.6V to (VCC1.2V) is recommended.
Unpredictable outputs may occur when the input is outside this range.
(5) Hysteresis amplifier
An input range of 0.6V to (VCC1.2V) is recommended.
Unpredictable outputs may occur when the input is outside this range.
(6) Thermal shutdown circuit
The thermal shutdown circuit puts the driver outputs (8,
6, 5, 3 pin) to the open state at the temperature of 175_C
(typical). The circuit is deactivated when the temperature
drops to about 155_C.
(7) Signal ground pin
Pins 1 and 24 are signal ground pins. Be noted that unpredictable outputs may occur if your application causes
a large current between pins 1 and 24 via the bonding
wire IC chip.
FApplication example
Fig.12
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Motor driver ICs
Electrical characteristic curves
External dimensions (Units: mm)
602
BA6970FS