ML4426
OUTPUTS
INPUT
STATE
LA
LB
LC
HA
HB
HC
SAMPLING
R
A
B
C
D
E
OFF
OFF
OFF
ON
ON
OFF
OFF
ON
OFF
OFF
OFF
OFF
ON
OFF
ON
ON
OFF
OFF
OFF
OFF
ON
ON
OFF
OFF
ON
ON
OFF
OFF
OFF
ON
N/A
FB B
FB A
FB C
FB B
FB A
FB C
OFF
OFF
OFF
OFF
ON
ON
OFF
OFF
OFF
ON
OFF
F
ON
Table 1. Commutation State Functions (Forward Direction)
A
B
C
D
E
F
A
B
C
D
E
F
HA
HB
HC
HIGH
SIDE
DRIVE
OUTPUTS
LA
LB
LOW
SIDE
DRIVE
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)
frequency corresponds to the maximum commutation
frequency or maximum motor speed when the VCO input
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
is equal to or slightly less than V . C
is calculated
REF
VCO
using the following equation:
6 HzFarad
(VCO constant, K ) is set by an 80.6kW resistor on R
v
VCO
6.5V 3.101 10
and a capacitor on C
as shown in Figure 5. R
sets
VCO
VCO
V
CVCO
=
up a current proportional the VCO input voltage at SPEED
FB. This current is used to charge and discharge C
between the threshold voltages of 2.3V and 4.3V. The
(2)
Hz
0.05
N SPEEDMAX
VCO
RPM
resulting triangle wave on C
corresponds to the clock
The closest standard value that is equal to or less than the
VCO
on VCO. K should be set so that the VCO output
calculated C should be used.
v
VCO
8
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
