ML4423
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
SINE and SINE Generators
A B
The capacitor to ground on C sets the frequency of the
sinewave according to the following relationship. C
should be a low temperature coefficient capacitor for
stable output frequency.
0
0
V
SPEED
R
SPEED
f
=
SINE
(1)
4C × 0.170V
0
V
falls below 9V.
DD
CIRCUIT BLOCKS AND COMPONENT SELECTION
For R
= 160kW
SPEED
R
REF
VSPEED
108,800 × C0
fSINE
=
(2)
R
C
should be set to 200kW. This current along with
REF
PWM
set the PWM frequency.
With V
= 3V and C = 0.47mF, f = 58.7Hz and
SINE
SPEED
0
Speed Control
can be observed at test points SINE (pin 10) and SINE
A
B
(pin 11).
The voltage on V
(pin 5) controls the sinewave
SPEED
frequency and amplitude. A 160kW resistor to ground on
PWM Generator
R
(pin 6) converts the voltage on V
to a current
SPEED
SPEED
which is used to control the frequency of the output PWM
sinewaves. The amplitude of the sinewaves increases
A triangular PWM frequency will be generated on a
capacitor to ground on C
(pin 13). The frequency is
PWM
linearly with V
until it reahces 4.4V. Above this
SPEED
set by the following equation:
voltage the amplitude remains constant and only the
frequency changes as shown in Figures 1 and 2.
1
f
=
PWM
(3)
200,000 × C
PWM
For C
= 220pF, f
= 22.7kHz. It is recommended
PWM
PWM
150
120
90
1.25
4.4V
1.00
0.75
0.50
0.25
60
R
C
SPEED = 160
= 0.47µF
0
30
0
0
2
4
6
8
2
4
6
8
V
(V)
V
(V)
SPEED
SPEED
Figure 1. Frequency vs V
Figure 2. Normalized Output Voltage vs V
SPEED
SPEED
5
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
