ml4423 Microsemi Corporation, ml4423 Datasheet - Page 5

• Manufacturer Part Number: ml4423
• Description: 3-phase Variable Speed Motor Controller
• Manufacturer: Microsemi Corporation

FUNCTIONAL DESCRIPTION
The ML4423 generates 2 reference sinewaves separated
by 90º or 60º in a closed loop feedback system. These
sinewaves can be varied in amplitude and frequency by
the speed input. Signals across the motor windings are fed
back and the ML4423 drives the external power output
stage with the PWM sinewave signal necessary to cause
the measured (feedback) output waveform to match the
internal reference sinewaves. The ML4423 provides fixed
period, variable duty cycle current limit protection, and
a programmable dead time circuit to prevent cross
conduction in the power output stage. An undervoltage
lockout circuit turns off the external power transistors if
V
CIRCUIT BLOCKS AND COMPONENT SELECTION
R
R
C
Speed Control
The voltage on V
frequency and amplitude. A 160k resistor to ground on
R
which is used to control the frequency of the output PWM
sinewaves. The amplitude of the sinewaves increases
linearly with V
voltage the amplitude remains constant and only the
frequency changes as shown in Figures 1 and 2.
DD
REF
REF
PWM
SPEED
should be set to 200k . This current along with
falls below 9V.
set the PWM frequency.
(pin 6) converts the voltage on V
150
120
90
60
30
0
Figure 1. Frequency vs V
SPEED
SPEED
until it reahces 4.4V. Above this
2
(pin 5) controls the sinewave
V
SPEED
4
(V)
R SPEED = 160
C 0 = 0.47 F
SPEED
SPEED
6
to a current
8
SINE
The capacitor to ground on C
sinewave according to the following relationship. C
should be a low temperature coefficient capacitor for
stable output frequency.
For R
With V
can be observed at test points SINE
(pin 11).
PWM Generator
A triangular PWM frequency will be generated on a
capacitor to ground on C
set by the following equation:
For C
A
Figure 2. Normalized Output Voltage vs V
SPEED
PWM
and SINE
SPEED
f
f
f
SINE
SINE
PWM
1.25
1.00
0.75
0.50
0.25
= 220pF, f
= 160k
0
= 3V and C
108 800
B
200 000
4
Generators
C
V
,
0
R
V
,
SPEED
PWM
SPEED
SPEED
2
0 170
.
0
1
PWM
= 22.7kHz. It is recommended
C
= 0.47 F, f
C
0
PWM
V
0
V
(pin 13). The frequency is
SPEED
sets the frequency of the
4
(V)
A
4.4V
(pin 10) and SINE
SINE
= 58.7Hz and
6
ML4423
SPEED
(1)
(3)
0
8
B
5