L6238 datasheet(11/35 Pages) STMICROELECTRONICS

11 / 35 page

2.4 Stuck Rotor/Monotonicity

Refer to figure 7. In order to alert the microproc-

essor of fault conditions, two bits are available in

the Serial Port’s Status Register.

1. Stuck Rotor

If the controller enters the Go mode after the Dou-

ble Align, Bemf must be detected within 419ms

when using a system clock frequency of 10MHz.

If this condition is not met, the outputs will be tris-

tated and set this bit to a zero. The controller en-

ters the ”Stuck Rotor Hold” state.

2. Mono

When the motor spins up normally, the resultant

S P IN SENSE pulses rise in frequency in a

monotonic pattern. Any fault condition that would

cause a rapid decrease in the SPIN SENSE fre-

quency would be detected by internal counters

setting the

MONO bit low and forcing a Brake

condition

2.5 External Sequencing

Although the user-defined Start-Up Algorithm is

flexible and will consistently spin up a motor with

minimum external interaction, the possibility ex-

ists where certain applications might require com-

plete microprocessor control of start-up.

The L6238 offers this capability via the SE-

QUENCE INCREMENT input. Referring to figure

9, with Output Enable and Run/Brake low, the

controller is in the ”Hold and Wait for Decision”

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 every

time that the SEQUENCER INCREMENT pin is

first brought low and then high. During the time

that this pin is high, all Bemf information is

Ru n

St uck

R o to r

(h ol d)

Ou t E na = 1

Ru nB r k = 1

Figure 7: Stuck Rotor/Monotonicity.

Brake

W/Mask

Hold & wait

for decision

Tri-state

W/Mask

Tri-state

W/Mask

RunBrk = 1

OutEna = 0

RunBrk = 1

OutEna = 1

RunBrk = 0

Run

W/Mask

Hold for

”Align & Go”

Power

Reset

RunBrk = 0

OutEna = 0

SeqInc = X

Hold

for

”Resync”

rk =

= 0

Run

Wo/Mask

SeqInc = 0

SeqInc = 1

SeqInc = 0

SeqInc = 1

Acti on across

line increments

sequencer

Auto Start-up

Enabled

Disabled

RunBrk = 1

OutEna = 0

RunBrk = 1

OutEna = 1

OutEna = 0

RunBrk = 0

Figure 8: Ext. Sequence.

L6238

11/35

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