BA6477FS [ROHM]
FDD spindle motor driver; FDD主轴电机驱动器
| 型号： | BA6477FS |
| 厂家： | 
ROHM |
| 描述： | FDD spindle motor driver |
| 文件： | 总12页 (文件大小：170K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Motor driver ICs
FDD spindle motor driver
BA6477FS
The BA6477FS is a one-chip IC designed for driving FDD spindle motors. This high-performance IC employs a 3-phase,
full-wave soft switching drive system, and contains a digital servo, an index amplifier, and a power save circuit. The com-
pactly packaged IC reduces the number of external components required.
FApplications
Floppy disk drivers
FFeatures
1) 3-phase, full-wave soft switching drive system.
2) Digital servo circuit.
4) Hall power supply switch.
5) Motor speed changeable.
6) Index amplifier.
3) Power save circuit.
FAbsolute maximum ratings (Ta = 25_C)
FRecommended operating conditions (Ta = 25_C)
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Motor driver ICs
BA6477FS
FBlock diagram
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Motor driver ICs
BA6477FS
FPin descriptions
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Motor driver ICs
FInput/output circuits
(1) Index input (1, 2 pin)
BA6477FS
(2) FG amplifier (3X5 pin)
(3) Speed control (6 pin)
(4) External clock input (7 pin)
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Motor driver ICs
BA6477FS
(5) Motor output (11X15 pin)
(6) Hall bias (16 pin)
(7) Hall input (17X22 pin)
(8) Integrating amplifier (28, 29 pin)
(9) Speed discriminator output (30 pin)
(10) Start/stop (31 pin)
(11) Index output (32 pin)
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Motor driver ICs
BA6477FS
FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 5V)
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Motor driver ICs
BA6477FS
FCircuit operation
(1) Motor drive circuit
minute voltage generated by the motor FG pattern and
produces a rectangular-shaped speed signal. The FG
amplifier gain (GFG = 42dB, typical) is determined by the
internal resistance ratio.
The motor driver is based on a 3-phase, full-wave soft
switching, current drive system in which the position of
rotor is sensed by Hall elements. The total drive current
of motor is sensed by a small resistor (RNF) and regulated
through a voltage comparison. The IC consists of Hall
amplifiers, an amplitude control circuit, a driver, an error
amplifier, and a current feedback amplifier (Fig. 1).
The waveforms of different steps along the signal path
from the Hall elements to the motor driver output are
shown in Fig. 2. The Hall amplifiers receive the Hall ele-
ments voltage signals as differential signals. Next, by de-
ducting the voltage signal of Hall elements 2 from the
voltage signal of Hall elements 1, current signal H1,
which has a phase 30 degrees ahead of Hall elements 1,
is created. Current signals H2 and H3 are created like-
wise. The amplitude control circuit then amplifies the H1,
H2, and H3 signal according to the current feedback am-
plifier signal. Then, drive current signals are produced at
A1, A2, and A3 by applying a constant magnification fac-
tor. Because a soft switching system is employed, the
drive current has low noise and a low total current ripple.
The total drive current is controlled by the error amplifier
input voltage. The error amplifier has a voltage gain of
about –11dB (a factor of 0.28). The current feedback am-
plifier regulates the total drive current, so that the error
amplifier output voltage (V1) is equal to the VRNF voltage,
which has been voltage-converted from the total drive
current through the RNF pin. If V1 exceeds the current lim-
iter voltage (Vcl), the constant voltage Vcl takes prece-
dence, and a current limit is applied at the level of
Vcl/RNF.
For noise filtering, a high-pass filter is given by C3 and a
resistor of 1.6kΩ (typical), and a low-pass filter is given
by C4 and a resistor of 200kΩ (typical). The cutoff fre-
quencies of high-pass and low-pass filters (fH and fL, re-
spectively) are given by:
1
1
fH =
fL =
2π 1.6kΩ C3
The C3 and C4 capacitances should be set so as to satis-
fy the following relationship:
2π 200kΩ C4
fHtfFGtfL
where fFG is the FG frequency. Note that the FG amplifier
inputs have a hysteresis.
The speed discriminator divides the reference clock and
compareswiththereferencefrequency, andthenoutputs
an error pulse according to the frequency difference. The
motorrotationalspeedNisgiveninthefollowingformula.
fosc
1
z
N = 60 S
S
(1)
n
fosc is the reference clock frequency,
n is (speed discriminator count) 2,
z is the FG tooth number.
The discriminator count depends on the speed control
pin voltage.
The current feedback amplifier tends to oscillate be-
cause it receives all the feedback with a gain of 0dB. To
prevent this oscillation, connect an external capacitor to
the CNF pin for phase compensation and for reducing the
high frequency gain.
The integrator flattens out the error pulse of the speed
discriminator and creates a control signal for the motor
drive circuit (Fig. 4).
(3) Index amplifier
(2) Speed control circuit
The index amplifier is a hysteresis amplifier with a typical
hysteresis width of +18mV and –22mV. The input pin is
not biased internally.
The speed control circuit is a non-adjustable digital servo
system that uses a frequency locked loop (FLL). The cir-
cuit consists of an 1/2 frequency divider, an FG amplifier,
and a speed discriminator (Fig. 3).
An internal reference is generated from an external clock
signal input. The 1/2 frequency divider reduces the fre-
quency of the OSC signal. The FG amplifier amplifies the
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Motor driver ICs
BA6477FS
(4) Other circuits
S Start/stop circuit
S Thermal shutdown circuit
The start/stop circuit puts the IC to the operating state
whenthecontrolpinisLOW, andtothestandbystate(cir-
cuit current is nearly zero) when the control pin is HIGH.
The Hall elements bias switch, which is linked to the
start/stop circuit, is turned off during the standby state,
so that the Hall device current is shut down.
This circuit shuts down the IC currents when the chip
junction temperature is increased to about 175_C (typi-
cal). The thermal shutdown circuit is deactivated when
the temperature drops to about 155_C (typical).
FCircuit operation
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Motor driver ICs
BA6477FS
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Motor driver ICs
BA6477FS
FOperation notes
(1) Thermal shutdown circuit
(4) Driver ground pin (pin 14)
This circuit shuts down all the IC currents when the chip
junction temperature is increased to about 175_C (typi-
cal). The thermal shutdown circuit is deactivated when
the temperature drops to about 155_C (typical).
(2) Hall elements connection
Pin 14, which is the motor current ground pin, is not con-
nected to the signal ground pin (pin 26). Design a proper
conductor pattern in consideration of the motor current
that flows through pin 14.
(5) External clock
Hall elements can be connected in either series or paral-
lel. When connecting in series, care must be taken not to
allow the Hall output to exceed the Hall common-mode
input range.
Make sure that the pin7 voltage is always less than VCC
and more than the ground voltage.
(3) Hall input level
Switching noise may occur if the Hall input voltage (pins
17X22) is too high. Differential inputs of about 100mVP-P
are recommended.
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Motor driver ICs
BA6477FS
FApplication example
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Motor driver ICs
BA6477FS
FElectrical characteristic curves
FExternal dimensions (Units: mm)
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