ML4411A Просмотр технического описания (PDF) - Micro Linear Corporation
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ML4411A Datasheet PDF : 14 Pages
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ML4411/ML4411A
STATE
N1
R OR 0
OFF
A
OFF
B
OFF
C
ON
D
ON
E
OFF
F
OFF
RESET
4.3 V
CVCO
2.3 V
OUTPUTS
N2
N3
P1
P2
ON
OFF
ON
OFF
OFF
ON
ON
OFF
OFF
ON
OFF
ON
OFF
OFF
OFF
ON
OFF
OFF
OFF
OFF
ON
OFF
OFF
OFF
ON
OFF
ON
OFF
Table 1. Commutation States.
INPUT
P3
SAMPLING
ON
N/A
OFF
PH2
OFF
PH1
OFF
PH3
ON
PH2
ON
PH1
OFF
PH3
VCO OUT
STATE R
0
A
B
C
D
E
F
A
Figure 5. Commutation Timing and Sequencing.
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.
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:
dVVCO ≈ IRAMP
dt
C1 + C2
since
FVCO = KVCO × VVCO
KVCO(MAX)
=
4 × 10−6
CVCO
then combining the 3 equations IRAMP can be calculated
from the desired maximum open loop stepping rate the
motor can follow.
IRAMP<
dFVCO
dt
CVCO × (C1 + C2)
4 × 10−6
7
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