L6238 datasheet(10/35 Pages) STMICROELECTRONICS

10 / 35 page

Assuming the motor is stationary, with Output

Enable high and Run/Brake low, the controller is

in the ”Hold for Align & GO” state. When

Run/Brake is brought high, the motor is in align

mode with Phase 1 active (Output A high and

Output B low).

Align is a zero. After the align

time-out (user-programmable), the

Align bit goes

high and the sequencer double increments the

outputs to Phase 3 (Output B high and Output C

low). After the next time-out, the controller enters

the Go mode, with the sequencer automatically

incrementing the output phase upon detection of

the motor’s Bemf.

Never command an Align & Go unless a refer-

ence signal is present at PLL FREF, since this

is the signal that determines the length of time

that phase 1 remains active.

If Run/Brake is brought low, (or if the 5V supply

is removed) the controller will revert to ”Hold for

Align & GO” and the serial port will be reinitial-

ized. In order to prevent an erroneous restart con-

dition, it is necessary that Run/Brake be held low

until the motor has completely stopped. Once the

motor has stopped, Run/Brake may be brought

high for a complete Align & Go Start-Up routine.

2.3 Resynchronization

If power is momentarily lost, the sequencer can

automatically resynchronize to the monitored

Bemf. This resychronization can either occur

whenever Output Enable is first brought low then

high or if the Logic Supply is momentarily lost.

Referring to figure 6, the ”Hold for Resync” state

is entered upon POR (Power On Reset) or when-

ever Output Enable is brought low. The control-

ler leaves this state and enters ”Start Resync”

when Output Enable is high.

If zero crossings are detected, the sequencer will

automatically lock on to the proper phase and

bring the motor speed up to Phase Lock.

This resynchronization will take effect with the

motor speed running as low as typically 30% of

it’s nominal value.

Never command an Align & Go while the mo-

tor is spinning. Always initiate a resync first

or initiate brake mode and allow the motor to

spin down.

Power

Reset

Hold

for

”Resync”

Start

”Resync”

Resync=1

Release

min mask

Run

Figure 6: Resync.

L6238

10/35

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