ML4426
OUTPUTS
STATE
R
A
B
C
D
E
F
LA
OFF
OFF
OFF
ON
ON
OFF
OFF
LB
ON
OFF
OFF
OFF
OFF
ON
ON
LC
OFF
ON
ON
OFF
OFF
OFF
OFF
HA
ON
ON
OFF
OFF
OFF
OFF
ON
HB
OFF
OFF
ON
ON
OFF
OFF
OFF
HC
ON
OFF
OFF
OFF
ON
ON
OFF
INPUT
SAMPLING
N/A
FB B
FB A
FB C
FB B
FB A
FB C
Table 1. Commutation State Functions (Forward Direction)
A
HA
HIGH
SIDE
DRIVE
OUTPUTS
B
C
D
E
F
A
B
C
D
E
F
HB
HC
LA
LOW
SIDE
DRIVE
OUTPUTS
LB
LC
Figure 4. Output Commutation Sequence Timing Diagram (Forward Direction)
Cycle 1 - Full Commutation, Cycle 2 - Commutation with 50% PWM Duty Cycle
FUNCTIONAL DESCRIPTION
Voltage Controlled Oscillator (VCO)
(Continued)
frequency corresponds to the maximum commutation
frequency or maximum motor speed when the VCO input
is equal to or slightly less than V
REF
. C
VCO
is calculated
using the following equation:
6.5V
3101
10
-
6
.
0.05
Hz
Farad
V
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, K
v
) is set by an 80.6kW resistor on R
VCO
and a capacitor on C
VCO
as shown in Figure 5. R
VCO
sets
up a current proportional the VCO input voltage at SPEED
FB. This current is used to charge and discharge C
VCO
between the threshold voltages of 2.3V and 4.3V. The
resulting triangle wave on C
VCO
corresponds to the clock
on VCO. K
v
should be set so that the VCO output
C
VCO
=
Hz
N
SPEED
MAX
RPM
(2)
The closest standard value that is equal to or less than the
calculated C
VCO
should be used.
8
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
