ml4423 Microsemi Corporation, ml4423 Datasheet - Page 6

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

ML4423
6
Current Limit
Motor current is sensed on I
be selected so that
For a 2A current limit, R
and 330pF capacitor filter (shown in figure 3) filter the
high frequency flyback pulses (due to the freewheeling
diode recovery currents) occurring at the output. When
I
the remainder of the current PWM cycle, which is
asynchronous with the sinewave frequency. Thus current
limit is fixed-period with variable duty cycle.
PWM SINE Controller
This circuit block compares the sinewaves at SINE
SINE
SENSE
drives the outputs to force these “differential” waveforms
to equal the internal reference waveforms at SINE
SINE
SENSE
peak maximum. The signals at these pins should be
filtered to remove the PWM frequency. The high voltages
at the motor terminals are divided down to 1.7V to
provide voltage feedback to the controller. In figure 3,
the resistors to ground from SENSE
(pin 3) should be 1k . SENSE
500 to ground because it has 1/2 the input impedance
of the other 2 inputs. The 0.15 F capacitors to ground on
SENSE
on SENSE
inputs. V
For the values shown in figure 3:
MAX
B
B
is reached the output power will be turned off for
. The differential signals SENSE
to the sampled inputs SENSE
B
B
A
–SENSE
–SENSE
and SENSE
(V
R
PEAK
V
C
LIMIT
PEAK
SPEED
will create a 1kHz low pass filter at these
on the motor is set by the divider ratios.
C
C
, respectively. The PWM loop then
= 4.4V)
will be approximately 1.7 volts zero-
I
0 5 .
MAX
1 7
170
1 7
B
.
.
V
and the 0.3 F capacitor to ground
V
V
V
LIMIT
99
49 5
k
.
1
SENSE
k
500
k
= 0.25 . The 1k
C
1
k
(pin 2) should have a
500
(pin 16). R
A
A
(pin 1) and SENSE
–SENSE
A
–SENSE
C
LIMIT
C
and
and
resistor
should
A
(4)
(5)
A
and
and
B
OUTPUT DRIVE
The 6 output drivers of the ML4423 drive the H and L
outputs from 0 to 12 volts (with pin 25 tied to V
The outputs will drive about 10mA and are designed to
drive output buffers and high side drivers requiring 12V
swings. The ML4423 provides lower current 0 to 5V drive
for high/low side drivers requiring 5V input signal swings
with pin 25 left unconnected.
PROGRAMMABLE DEADTIME
A dead time circuit is provided to prevent shoot through
currents in the power output stage. The dead time is
controlled by a resistor to ground on R
time selected should be large enough to prevent cross
conduction between the upper and lower power devices
of each inverter phase leg.
With f
= 166k, t
C
These two external capacitors to ground each set a pole in
the forward path of the feedback loop in conjunction with
a g
higher than the PWM frequency.
APPLICATION
The ML4423 provides all the signals necessary to drive
the output power stage connected to the motor. The
components around the ML4423 for a typical application
are shown in figure 3. The motor DC supply voltage
should be greater than the largest signal waveform
required or output clipping may result. Figure 4 shows an
alternate circuit using the IR2118.
GM1
m
of 1/650 . The pole should be placed at a frequency
PWM
and C
t
2
DEAD
DEAD
g
= 25kHz, the PWM period is 40 s. With R
C
m
GM2
g m
= 2 s (~5%).
1 2 10
.
f
PWM
11
R
DB
DT
(pin 9). The dead
CC
+(12V)).
(6)
(7)
DB