L7250
2
SPINDLE MOTOR CONTROLLER
Figure 3.
SUPPLY
VOLTAGE
COMPENSATION
VM
SMOOTHDRIVE
MODULATED
DUTY CYCLE
ADC
KVAL
SMOOTHDRIVE
RAW
DUTY CYCLE
REGISTER
START-OF-COUNT
TIME DOMAIN
DUTY CYCLE
SIGNALS
KVAL
VM
VM
VM
HGU
SMOOTHDRIVE
6 State
or
FET
GATE
DRIVE
MOTU
PROFILE
MEMORY/
LOGIC
DIGITAL
MULTIPLIER
COUNTER
&
COMPARATORS
Sine
LGU
Mode
MEMORY
ADDRESS
COUNTER
(N=48)
COARSE
PHASE
ADVANCE
BITS
HGV
MOTV
LGV
FET
GATE
DRIVE
WINDOW
TRISTATE
CMD
LOADCP
BIT
FSCAN
SPINDLE
MOTOR
OLSIX/OLSIN
HGW
MOTW
LGW
OR CLSIX/CLSIN
FET
GATE
DRIVE
ADVANCE
BIT
BEMF
COMP.
ZERO
WINDOW
MASK
FINE
PHASE
ADVANCE
BITS
CROSSING
PERIOD
FSCAN
COUNTER
Tc
ZC
CTAP
COUNTER
16+4 BIT
xx
xx
PWM MASK
CURRENT
LIMIT
COMP.
SPSENH
SYSCLK
16.5MHZ
MASK
REGISTERS
CUR DAC
2.1 Spindle Smoothdrive Functionality
L7250 utilizes ST's proprietary Smoothdrive commutation algorithm. Smoothdrive is a voltage mode pseudo-
sinusoidal spindle drive scheme where the duty cycles of the three windings are modulated to form sinusoidal
voltages across each winding. The system determines the shape and amplitude of the driving voltages in a
completely digital manner.
2.2 SYSCLK
The Smoothdrive system clock comes through the SYSCLK pin.
The system expects either 33MHz or 16.5MHz on this pin, and needs 16.5MHz internally. A SYSCLK divide by
two can be enabled by a SPI register bit PRESMO to accomodate a 33MHz external clock.
2.3 Smoothdrive Wave shape
The basic Smooth drive wave shape is stored in digital memory. A voltage profile designed to reduce switching
losses and increase the voltage headroom has been implemented. Essentially, two phases are PWM'ed, while
the low side driver of the third phase is on at 100% duty cycle. The PWM duty cycles are modulated in such a
way as to result in sinusoidal currents on all 3 motor phases. Driving in this manner, as opposed to driving true
sinusoids on all three phases, results in improved headroom and efficiency, approaching that of conventional 6
state commutation.
The system is phase locked to the motor by sensing one BEMF zero crossing on one winding, once per electrical
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STMICROELECTRONICS [ ST ]
