ML4411 Ver la hoja de datos (PDF) - Micro Linear Corporation
Número de pieza
componentes Descripción
Fabricante
ML4411 Datasheet PDF : 14 Pages
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Minute.
ML4411/ML4411A The minimum VCO gain derived from the specification
table (using the minimum Fvco at VVCO = 6V) is:
KVCO(MIN)
=
2.42 × 10−6
CVCO
Assuming that the VVCO(MAX) = 9.5V, then
CVCO
=
9.5 ×
2.42 × 10−6
FMAX
or
CVCO
=
460
POLES × RPM
µF
3000
2500
2000
1500
1000
0.01µF
0.02µF
500
0
0
2
4
6
8
10
12
VVCO (VOLTS)
Figure 3. VCO Output Frequency vs. VVCO (Pin 20)
Figure 4 shows the transfer function of the Phase Lock
Loop with the phase detector formed from the sampled
phase through the Gm amplifier with the loop filtered
formed by R, C1, and C2.
The impedance of the loop filter is
ZRC (s)
=
1
C1s
(s + ωLEAD)
(s + ωLAG)
SAMPLED
PHASE
Gm = 1.25 x 10–4
+
RC ZRC
–
R
FOUT
VCO
C1
C2
KVCO(HZ/V)
Figure 4. Back EMF Phase Lock Loop Components
Where the lead and lag frequencies are set by:
ωLEAD
=
1
R C2
ωLAG
=
C1 + C2
R C1C2
6
START-UP SEQUENCING
When the motor is initially at rest, it is generating no
back-EMF. Because a back-EMF signal is required for
closed loop commutation, the motor must be started
“open-loop” until a velocity sufficient to generate some
back-EMF is attained (around 100 RPM). The following
steps are a typical procedure for starting a motor which is
at rest.
Step 1: The IC is held in reset (state R) with full power
applied to the windings (see figure 6). This aligns the rotor
to a position which is 30° (electrical) before the center of
the first commutation state.
Step 2: Reset is released, and a fixed current is input to
pin 21 and appears as a current on pin 20, and will ramp
the VCO input voltage, accelerating the motor at a fixed
rate.
Step 3: When the motor speed reaches about 100 RPM,
the back EMF loop can be closed by pulling pin 18 high.
RESET/
ALIGN
P1, P3, N2 ON
OPEN-LOOP
(STEPPING)
CLOSED LOOP
0
RESET
ENABLE E/A
Figure 6. Typical Start-up Sequence.
Using this technique, some reverse rotation is possible.
The maximum amount of reverse rotation is 360/N, where
N is the number of poles. For an 8 pole motor, 45° reverse
rotation is possible.
For quick recovery following a momentary power failure,
the following steps can be taken:
STEP
1
2
3
PIN PIN PIN
16
18
21
0
0 FIXED
1
0 FIXED
1
1
0
Table 2. Start-up Sequence.
ILIMIT
ICMD
IMAX
IMAX
IMAX
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