ML4423 Просмотр технического описания (PDF) - Micro Linear Corporation
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ML4423 Datasheet PDF : 10 Pages
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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 160kW 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.
ML4423
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.
VSPEED
fSINE
=
RSPEED
4C0 × 0.170V
(1)
For RSPEED = 160kW
fSINE
=
VSPEED
108,800 ×
C0
(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:
fPWM
=
1
200,000 × CPWM
(3)
For CPWM = 220pF, fPWM = 22.7kHz. It is recommended
150
120
90
60
RSPEED = 160
C0 = 0.47µF
30
0
2
4
6
8
VSPEED (V)
Figure 1. Frequency vs VSPEED
1.25
1.00
0.75
0.50
0.25
4.4V
0
2
4
6
8
VSPEED (V)
Figure 2. Normalized Output Voltage vs VSPEED
5
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