ML4426 データシートの表示（PDF） - Micro Linear Corporation
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ML4426 Datasheet PDF : 16 Pages
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ML4426
STATE
R
A
B
C
D
E
F
OUTPUTS
LA
LB
LC
HA
HB
HC
OFF
ON
OFF
ON
OFF
ON
OFF
OFF
ON
ON
OFF
OFF
OFF
OFF
ON
OFF
ON
OFF
ON
OFF
OFF
OFF
ON
OFF
ON
OFF
OFF
OFF
OFF
ON
OFF
ON
OFF
OFF
OFF
ON
OFF
ON
OFF
ON
OFF
OFF
Table 1. Commutation State Functions (Forward Direction)
A
B
CD
E
F
A
B
C
D
HA
HIGH
SIDE
DRIVE
HB
OUTPUTS
HC
INPUT
SAMPLING
N/A
FB B
FB A
FB C
FB B
FB A
FB C
E
F
LA
LOW
SIDE
DRIVE
LB
OUTPUTS
LC
Figure 4. Output Commutation Sequence Timing Diagram (Forward Direction)
Cycle 1 - Full Commutation, Cycle 2 - Commutation with 50% PWM Duty Cycle
FUNCTIONAL DESCRIPTION (Continued)
Voltage Controlled Oscillator (VCO)
The VCO provides a TTL compatible clock output on the
VCO/TACH pin proportional to the VCO input voltage at
the SPEED FB pin. The proportion of frequency to voltage
(VCO constant, Kv) is set by an 80.6kW resistor on RVCO
and a capacitor on CVCO as shown in Figure 5. RVCO sets
up a current proportional the VCO input voltage at SPEED
FB. This current is used to charge and discharge CVCO
between the threshold voltages of 2.3V and 4.3V. The
resulting triangle wave on CVCO corresponds to the clock
on VCO. Kv should be set so that the VCO output
frequency corresponds to the maximum commutation
frequency or maximum motor speed when the VCO input
is equal to or slightly less than VREF. CVCO is calculated
using the following equation:
6.5V 3.101 10-6 Hz Farad
CVCO =
V
0.05 Hz
RPM
N
SPEEDMAX
(2)
The closest standard value that is equal to or less than the
calculated CVCO should be used.
8
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