ML4423CS datasheet(6/10 Pages) MICRO-LINEAR

6 / 10 page

ML4423

Current Limit

Motor current is sensed on ISENSE (pin 16). RLIMIT should

be selected so that

LIMIT

MAX

= 05

(4)

For a 2A current limit, RLIMIT = 0.25W. The 1kW resistor

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

IMAX is reached the output power will be turned off for

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 SINEA and

SINEB to the sampled inputs SENSEA–SENSEC and

SENSEB–SENSEC, respectively. The PWM loop then

drives the outputs to force these “differential” waveforms

to equal the internal reference waveforms at SINEA and

SINEB. The differential signals SENSEA–SENSEC and

SENSEB–SENSEC will be approximately 1.7 volts zero-

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 SENSEA (pin 1) and SENSEB

(pin 3) should be 1k

W. SENSEC (pin 2) should have a

500

W to ground because it has 1/2 the input impedance

of the other 2 inputs. The 0.15

mF capacitors to ground on

SENSEA and SENSEB and the 0.3mF capacitor to ground

on SENSEC will create a 1kHz low pass filter at these

inputs. VPEAK on the motor is set by the divider ratios.

For the values shown in figure 3:

(VSPEED = 4.4V)

PEAK

















49 5

500

170

(5)

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 VCC+(12V)).

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 RDT (pin 9). The dead

time selected should be large enough to prevent cross

conduction between the upper and lower power devices

of each inverter phase leg.

DEAD

=×

()

−

12 10 11

(6)

With fPWM = 25kHz, the PWM period is 40ms. With RDB

= 166k, tDEAD = 2ms (~5%).

CGM1 and CGM2

These two external capacitors to ground each set a pole in

the forward path of the feedback loop in conjunction with

a gm of 1/650W. The pole should be placed at a frequency

higher than the PWM frequency.

PWM

(7)

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.

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