LX1722 データシートの表示（PDF） - Microsemi Corporation
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LX1722 Datasheet PDF : 14 Pages
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INTEGRATED PRODUCTS
AudioMAX™
LX1721 / 1722
Class-D Stereo Power Amplifier Controller
PRODUCTION
APPLICATION INFORMATION
Frequency Synchronization
Two or more LX1721 / LX1722 oscillators can be configured for
synchronous operation. One unit, the master, is programmed for
the desired frequency with the RPWM and CPWM as usual.
Additional units will be slave units, and their oscillators will be
disabled by leaving the RPWM pin disconnected. The CLOCK pin
and the CPWM pin of the slave units should be tied to the CLOCK
pin and the CPWM pin of the master unit respectively. In this
configuration, the CLOCK pins of the slave units begin receiving
instead of transmitting clock pulses. Also, the CPWM pins quit
driving the PWM capacitor in the slave units. Note that for
optimum performance, all slave units should be located within a
few inches of the master unit.
Oscillator Configuration (RPWM and CPWM selection)
The oscillator is programmed by the external timing components
RPWM and CPWM. For a nominal frequency of 333kHz, RPWM and
CPWM should be set to 49.9kOhms and 100pF respectively. Note that
in order to keep the slope of the PWM ramp voltage proportional to
the supply voltage, both the ramp peak and valley voltages, and the
charge and discharge currents are proportional to the supply voltage.
This keeps the frequency relatively constant while keeping the slope
of the PWM ramp proportional to the voltage on the VDD pin. For
operating frequencies other than 333kHz, the frequency can be
approximated by the following equation:
Frequency
=
1
(0.577)(RPWM )(CPWM )
+
320ns
Copyright © 2001
Rev. 1.2a,2004-06-10
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
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