User guide

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65
Crystal
The AL4020 requires a 16MHz, fundamental mode crystal. A tuning
capacitance of approximately 12pF is suggested between each crystal
connection and Ground. The inherent pcb and lead capacitance must
be included in this.
EMC
There are two major considerations in reducing the electromagnetic
radiation generated by the AL4020.
The device tends to generate noise at the third harmonic of the
crystal (48MHz). Adding the crystal capacitors detailed above
reduces this to acceptable limits.
Broad band noise can be reduced by good decoupling. A range of
22uF aluminium capacitors and 0u1 ceramic capacitors should be used
on the circuit board. A 560pF ceramic capacitor should also be
connected across the AL4005 power pins as close as possible to the
device.
The use of 150uH inductors in series with all three DMX512 signals
is also an effective way to reduce conducted emissions.
Application
The following circuit shows the AL4020 application drawing.