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L7250

Figure 6. Synchronization to Smooth Drive Commutation

2.7.4 Closed Loop Commutation

During closed loop commutation, the motor is driven following the smooth driver wave shape (or the traditional

six step profile). To keep sync, each electrical cycle a winding of the spindle motor (phase U) is tri-stated, for a

programmable (via SPI) window (W), to sense for the ZC occurrence; to mask the current flyback time a mask-

ing time is applied starting from the opened window for a certain number M of samples (settable via SPI). Due

to the fact that the motor winding is driven in voltage mode a control of the phase shift between the applied volt-

age and the Bemf is required in order to optimize the system efficiency (the loss in efficiency is related to the

cosine of the angle between Bemf and current). Via the SPI it is possible to set an appropriate Torque Optimizer

(TO) value based on the application characteristics (Rm, Lm, Speed).

When a ZC is detected the circuit starts scanning the stored smooth drive wave shape (or the traditional six step

profile) from the number of sample pointed by the TO register; the tri-stated window is opened a certain number

of samples before.

In the following table the relation between the TO register contents and the window and masking time position

and duration:

start

stop

window

TO-W

At ZC detection

mask

TO-W

TO-W+M

Set Load Coarse Phase

Write Reg.07H

LoadCP = 1

(*1)

Wait Loop

(300 usec)

START

Sync. To SmoothDrive Commutation

i=0

Wait Rising Edge

of ZC (pin 22)

EXIT

Sync. To Smooth

Drive Commutation

Set Load Coarse Phase

Write Reg.07H

LoadCP = 1

(*2)

NO

i = 2

YES

NO

YES

Set CLCOAST

Write Reg.03H

Spstate[3:0]=0000

Motor Running in

Sine or Six

Set Closed Loop SINE

Write Reg.03H

Spstate[3:0] =0111

Set Closed Loop SIX

Write Reg.03H

Spstate[3:0] =0110

SINE

SIX

(*5)

(*6)

(*7a)

(*7b)

Time Out

Control

NO

START UP

FAILURE

Exit

YES

Set OLCOAST

Write Reg.03H

Spstate[3:0]=0001

Wait Loop

(30 usec)

ZC_SamplingRoutine

BEGIN

ZC_SamplingRoutine

END

Reset Time Out

Reset Time Out

(*3)

(*4)

Inc i

CALL

ZC_SamplingTime

Routine

CALL

ZC_SamplingTime

Routine