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ML4428IP Datasheet(PDF) 10 Page - Micro Linear Corporation

Part # ML4428IP
Description  Sensorless Smart-Start??BLDC PWM Motor Controller
PDF  16 Pages
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Manufacturer  MICRO-LINEAR [Micro Linear Corporation]
Direct Link  http://www.microlinear.com
Logo MICRO-LINEAR - Micro Linear Corporation

ML4428IP Datasheet(HTML) 10 Page - Micro Linear Corporation

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10
ML4428
CSNS
A capacitor to ground at this pin sets the ON time of the 6
current sense pulses used for position detection at start-up
and at low speeds. The ON time is set by:
TON = CSNS (35.7k)
Referring to Figure 5, each of the 6 current sense pulses is
governed by a rise time with a time constant of L/R where L
is the inductance of the motor network with 2 windings
shorted and R is the total resistance in series with the motor
between the supply rails. R includes the ON-resistance of
the power-FETs and RSNS. The RDSON of the high side FET
should match that of the low side FET. L is a function of
rotor position. Each pulse will have a peak value
VSENSEPEAK of
VR
V
R
SENSEPEAK
SNS
MOTOR
T
e
ON
LR
=−
−
1
/
where
RR
R
R
LL
L L
SDON
SENSE
LL
=×
+ ×
()+
=×
−
−
075
2
075
.
.
What is important for sensing rotor position is the
amplitude difference between each of the three pairs of
current sense pulses. This can be seen by triggering on
ISNS on an oscilloscope with the RCVCO pin shorted to
ground. One should see the current waveform of Figure 5.
Allowing the peak current sense pulse to reach an
amplitude of 0.5V (by adjusting CSNS, and hence TON) or,
allowing the difference between the maximum and
minimum of the 6 pulses to be >50mV, should suffice for
adequate rotor position sensing. A good starting value for
TON is 200µs, requiring CSNS = 5.6nF.
RINIT
The initial time interval between sample pulses during
start-up is set by RINIT. This time interval (tINIT) occurs
while the RCVCO pin is less than 0.25 volts.
R
t
C
INIT
INIT
VCO
=
343
.
AB
C
D
E
F
A
3.75V
CVCO
2.0V
VCO OUT
Figure 6. Commutation Timing and Sequencing.
DIRECTION
OUTPUTS
INPUT SAMPLES
STATE
REVERSE
N3
N2
N1
P3
P2
P1
FORWARD
N1
N2
N3
P1
P2
P3
FORWARD
REVERSE
A
OFF
OFF
ON
ON
OFF
OFF
PH2
PH2
B
OFF
OFF
ON
OFF
ON
OFF
PH1
PH3
C
ON
OFF
OFF
OFF
ON
OFF
PH3
PH1
D
ON
OFF
OFF
OFF
OFF
ON
PH2
PH2
E
OFF
ON
OFF
OFF
OFF
ON
PH1
PH3
F
OFF
ON
OFF
ON
OFF
OFF
PH3
PH1
Table 1. Commutation States.



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