ML4411CS datasheet(7/14 Pages) MICRO-LINEAR

7 / 14 page

ML4411/ML4411A

OUTPUTS

INPUT

STATE

SAMPLING

R OR 0

OFF

N/A

OFF

PH2

OFF

PH1

OFF

PH3

OFF

PH2

OFF

PH1

OFF

PH3

Table 1. Commutation States.

RESET

4.3 V

CVCO

2.3 V

VCO OUT

STATE

Figure 5. Commutation Timing and Sequencing.

ADJUSTING OPEN LOOP STEP RATE

IRAMP should be set so that the VCO’s frequency ramp

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

(VPIN 20) ramp rate is given by:

VCO

RAMP

≈

since

VCO

=×

VCO MAX

VCO

() =

× −

410 6

then combining the 3 equations IRAMP can be calculated

from the desired maximum open loop stepping rate the

motor can follow.

RAMP

VCO

×+

× −

()

410

Step 1a: The IC is held in reset (state R) with ICMD low

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

up with ICMD or ILIMIT.

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