ML4423CS datasheet(5/10 Pages) MICRO-LINEAR

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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

VDD falls below 9V.

CIRCUIT BLOCKS AND COMPONENT SELECTION

RREF

RREF should be set to 200kW. This current along with

CPWM set the PWM frequency.

Speed Control

The voltage on VSPEED (pin 5) controls the sinewave

frequency and amplitude. A 160k

W resistor to ground on

RSPEED (pin 6) converts the voltage on VSPEED to a current

which is used to control the frequency of the output PWM

sinewaves. The amplitude of the sinewaves increases

linearly with VSPEED until it reahces 4.4V. Above this

voltage the amplitude remains constant and only the

frequency changes as shown in Figures 1 and 2.

SINEA and SINEB Generators

The capacitor to ground on C0 sets the frequency of the

sinewave according to the following relationship. C0

should be a low temperature coefficient capacitor for

stable output frequency.

SINE

SPEED

















0 170

(1)

For RSPEED = 160kW

SINE

SPEED

108 800

(2)

With VSPEED = 3V and C0 = 0.47mF, fSINE = 58.7Hz and

can be observed at test points SINEA (pin 10) and SINEB

(pin 11).

PWM Generator

A triangular PWM frequency will be generated on a

capacitor to ground on CPWM (pin 13). The frequency is

set by the following equation:

PWM

200 000

(3)

For CPWM = 220pF, fPWM = 22.7kHz. It is recommended

150

120

VSPEED (V)

RSPEED = 160

C0 = 0.47µF

1.25

1.00

0.75

0.50

0.25

4.4V

VSPEED (V)

Figure 1. Frequency vs VSPEED

Figure 2. Normalized Output Voltage vs VSPEED

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