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L7250

Sense, to determine rotor position, Open Loop Commutation, which accelerates the motor to build up BEMF,

Synchronization , to measure motor speed and position, initializing the Smoothdrive system, and Closed Loop

Smoothdrive Commutation, the normal synchronous commutation mode to accelerate and run at speed.

2.7.1 Inductive Position Sense

Inductive position sensing is achieved through a firmware routine that measures the current rise time in each of

the six possible states (six steps profile), and uses this information to determine the rotor position.

The six steps profile still comes from the Profile Memory that contains 48 samples, but in this case there are

only six different configuration, each of them repeated eight times; the linear scansion of the memory one sam-

ple at a time gives a new six step configuration every eight increments.

Before any operation can be done, the firmware routine must set the KVAL value present in SPI to the maximum

value (*1) , to saturate the PWM signals given to the motor, and put the Memory Address Counter in a known

position (*3); this is done keeping the motor in OLCOAST (*2) state and asserting a LoadCP command (*4) to

load the content of the torque optimizer related SPI register into the Memory Address Counter.

At this point, the present six steps configuration can be energized through the INDSENSE state (*5) , waiting

for the current to reach the threshold programmable via SPI (*6); the current limiting comparator will be triggered

by this condition, and it's output will be visible at ZC pad. The current rise time will be measured and stored from

the ASIC (*7) .

The device automatically limits the PWM signals for the three phases to limit the current, but the currents in the

windings must be recirculated from firmware putting the motor in OLCOAST (*8) state.

A burst of eight ADVANCE signals (*9) must be asserted from SPI to reach the next configuration in the profile

memory, then the procedure can be repeated. Each winding can be excited more than one time, to average the

measurements, and at the end of the sensing sequence the ASIC decides the rotor position.

Figure 4. Inductive Sense Routine

Set KVAL

Write Reg.08H

Kv[7:0] = 11111111

Measure Current

Rise Time

By reading the

ZC (pin 22)

Set OLCOAST

Write Reg.03H

Spstate[3:0] = 0001

Set Torque Optimizer

Write Reg.07H

TO[4:0] = 00000

Set Load Coarse Phase

Write Reg.07H

LoadCP = 1

Set ADVANCE

Write Reg.07H

Advance = 1

Set INDUCTIVE SENSE

Write Reg.03H

Spstate[3:0] = 0101

Store the measured

Current Rise Time

& Nph associated

Set OLCOAST

Write Reg.03H

Spstate[3:0] = 0001

START

Inductive Sense Routine

Nadv=0 , Nph=0

Nadv=8

Inc Nadv

Inc Nph

Nph

Compare the Six

Measured Rise Time

to define the

ROTOR POSITION

EXIT

Inductive Sense

Routine

Wait for

Current Decay

Nadv=0

ZC=0

ZC=1

NO

YES

YES

NO

(*1)

(*2)

(*3)

(*4)

(*5)

(*6)

(*7)

(*8)

(*9)