ML4425CH Micro Linear, ML4425CH Datasheet - Page 8

• Manufacturer Part Number: ML4425CH
• Description: Sensorless BLDC Motor Controller
• Manufacturer: Micro Linear

ML4425
FUNCTIONAL DESCRIPTION
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, K
and a capacitor on C
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
resulting triangle wave on C
on VCO. K
8
OUTPUTS
OUTPUTS
STATE
DRIVE
DRIVE
HIGH
LOW
SIDE
SIDE
A
C
D
R
B
E
F
v
should be set so that the VCO output
v
) is set by an 80.6k
HA
HC
HB
Cycle 1 - Full Commutation, Cycle 2 - Commutation with 50% PWM Duty Cycle
LA
LC
LB
VCO
OFF
OFF
OFF
OFF
OFF
ON
ON
LA
as shown in Figure 5. R
VCO
A
Figure 4. Output Commutation Sequence Timing Diagram
corresponds to the clock
B
OFF
OFF
OFF
OFF
ON
ON
ON
LB
resistor on R
Table 1. Commutation State Functions
C
(Continued)
VCO
VCO
D
OFF
OFF
OFF
OFF
OFF
VCO
ON
ON
LC
sets
OUTPUTS
E
frequency corresponds to the maximum commutation
frequency or maximum motor speed when the VCO input
is equal to or slightly less than V
using the following equation:
The closest standard value that is equal to or less than the
calculated C
OFF
OFF
OFF
OFF
ON
ON
ON
HA
F
C
VCO
A
=
6 5
VCO
.
0 05
V
.
OFF
OFF
OFF
OFF
OFF
ON
ON
HB
™
should be used.
B
RPM
3101 10
Hz
.
™ ™
™
N SPEED
C
-
6
OFF
OFF
OFF
OFF
ON
ON
ON
HC
Hz Farad
REF
D
œ
V
MAX
. C
VCO
E
SAMPLING
is calculated
INPUT
FB A
FB C
FB A
FB C
FB B
FB B
N/A
F
(2)