7

ML4411/ML4411A

OUTPUTS

INPUT

STATE

N1

N2

N3

P1

P2

P3

SAMPLING

R OR 0

OFF

ON

OFF

ON

OFF

ON

N/A

A

OFF

OFF

ON

ON

OFF

OFF

PH2

B

OFF

OFF

ON

OFF

ON

OFF

PH1

C

ON

OFF

OFF

OFF

ON

OFF

PH3

D

ON

OFF

OFF

OFF

OFF

ON

PH2

E

OFF

ON

OFF

OFF

OFF

ON

PH1

F

OFF

ON

OFF

ON

OFF

OFF

PH3

Table 1. Commutation States.

R

RESET

0A

B

C

D

E

F

A

4.3 V

2.3 V

VCO OUT

STATE

Figure 5. Commutation Timing and Sequencing.

ADJUSTING OPEN LOOP STEP RATE

during “open loop stepping” phase of motor starting is less

than the motor’s acceleration rate. In other words, the

motor must be able to keep up with the VCO’s ramp rate

in open loop stepping mode. The VCO’s input voltage

dV

dt

I

CC

VCO

RAMP

≈

+

12

since

FK

V

VCO

VCO

VCO

=×

K

C

VCO MAX

VCO

from the desired maximum open loop stepping rate the

motor can follow.

I

dF

dt

CC

C

RAMP

VCO

VCO

<

×+

()

12

6

410

and DIS PWR low. The Micro Processor monitors the VCO/

TACH OUT pin to determine if a signal is present. If a

signal is present, the frequency is determined (by

measuring the period). If a signal is not present, proceed

to the routine described above for starting a motor which

is a rest.

Step 2a: Release RESET and DIS PWR. Apply a current to

pin 21 and monitor the VCO/TACH OUT pin for VCO

frequency.

Step 3a: When the VCO frequency approaches 6 X the

motor frequency (or where the motor frequency has

decelerated to by coasting during the time the VCO

frequency was ramping up) the back EMF loop can be

closed by pulling pin 18 high and motor current brought