L6238S datasheet(12/31 Pages) STMICROELECTRONICS

12 / 31 page

If zero crossings are detected, the sequencer will

automatically lock on to the proper phase.

This resynchronization will take effect with the

motor speed running as low as typically 30% of

it’s nominal value.

2.5 External Sequencing

Although the user-defined Start-Up Algorithm is

flexible and will consistently spin up a motor with

no external interaction, the possibility exists

where certain applications might require complete

microprocessor control of start-up.

The L6238S offers this capability via the SE-

QUENCE INCREMENT input. Referring to figure

2-5, during initial power-up with Output Enable

low, the controller is in the ”Hold and Wait for De-

cision” state. If the SEQUENCE INCREMENT pin

is brought high during this state, the Auto StartUp

Algorithm is disabled and the sequencer can be

controlled externally.

When Output Enable and Run/Brake are

brought high, the sequencer is incremented on

each positive transition o the SEQUENCER IN-

CREMENT pin. During the time that this pin is

high, all Bemf information is masked out. When it

is low, the Bemf information can be detected nor-

mally after the internal mask time. The minimum

mask time is 192/Sys_Clk (i.e. with Sys_Clk =

10MHz, min. mask = 19.2

µs) Therefore to insure

that the sequencer is under complete control of

the state machine, the time that the SEQUENCE

INCREMENT pin is held low should be much less

then the min. mask time, but greater then 1

µs.

When the motor has reached a predetermined

speed, the SEQUENCE INCREMENT pin can be

left low and the L6238S Motor Control logic will

take over and automatically spin up the motor to

the desired speed

3.0 START-UP ALGORITHMS

3.1 Spin-Up Operation

The spin operation can be separated into 3 parts:

1) Open Loop Start-Up - The object is to create

motion in the desired direction so that the Bemf

voltages at the 3 motor terminals can provide reli-

able information enabling a transition to closed

loop operation.

STATE=1

DRIVERS OFF

MIN CLOCK DELAY

PERIOD STOP

DELAY STOP

MASK STOP

INT START-UP DISABLED

MIN CLOCK DELAY

LOAD MIN DELAY

LOAD MIN MASK

MASK COUNT

SEQINC=1 &

OUTENA=0

RUN/BRK=X

D95IN313

*VALID IF SEQINC=0, AND DELAY TIMES OUT

**CLOCK DELAY=F(TDLY_[2:0])

WHEN BEMF PERIOD <3.3ms @ 10MHz (SPEED >12.7Hz FOR 8 POLES)

SEQINC=0

STATE=STATE+1

MASK COUNT

LOAD DELAY=PERIOD

LOAD MASK=PERIOD

RESET PERIOD

PERIOD COUNT

DELAY COUNT**

BEMF

POR=0

FROM ANY STATE

DRIVERS ON

PERIOD COUNT

DELAY COUNT

SEQINC=0

BEMF

SEQINC=1

STATE=STATE+1

SEQINC=1

FROM ANY STATE

WITH SEQ_INC=0

RETURN TO

PREVIOUS STATE

(CHANGING SEQINC=1)

RUN/BRK=1 &

OUTENA=1

SEQINC=1

Figure 2-5

L6238S

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