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L7250

2

SPINDLE MOTOR CONTROLLER

Figure 3.

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

VM

HGU

MOTU

LGU

FET

GATE

DRIVE

VM

HGV

MOTV

LGV

FET

GATE

DRIVE

VM

HGW

MOTW

LGW

FET

GATE

DRIVE

xx

SMOOTHDRIVE

PROFILE

MEMORY/

LOGIC

MEMORY

ADDRESS

COUNTER

(N=48)

DIGITAL

MULTIPLIER

COUNTER

&

COMPARATORS

xx

CTAP

WINDOW

MASK

PWM MASK

ZERO

CROSSING

PERIOD

COUNTER

16+4 BIT

FSCAN

COUNTER

ZC

Tc

FSCAN

BEMF

COMP.

CURRENT

LIMIT

COMP.

ADVANCE

BIT

OLSIX/OLSIN

OR CLSIX/CLSIN

KVAL

REGISTER

KVAL

COARSE

PHASE

ADVANCE

BITS

FINE

PHASE

ADVANCE

BITS

SYSCLK

16.5MHZ

SPINDLE

MOTOR

LOADCP

BIT

SMOOTHDRIVE

RAW

DUTY CYCLE

SMOOTHDRIVE

MODULATED

DUTY CYCLE

TIME DOMAIN

DUTY CYCLE

SIGNALS

SPSENH

VM

ADC

START-OF-COUNT

SUPPLY

VOLTAGE

COMPENSATION

MASK

REGISTERS

WINDOW

TRISTATE

CMD

6 State

or

Sine

Mode

CUR DAC