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Frequency:
As could be seen in figure 3 the higher the frequency the lower is the
ripple current. Therefore the effective coil voltage could be chosen to
be lower with keeping all the other parameters constant. We recommend a PWM frequency of minimum 20kHz.

The application of PWM voltage across the relay coil causes magnetostriction of the iron within the relay magnetic system (core/frame/armature). The result is a slight audible noise if the relay was freely
suspended. However when the relay soldered or welded onto a rigid
lead frame that noise might be amplified. This depends on the lead
frame (suspension, dimension, etc.) and the sound propagation and
damping within the car. Choosing 20kHz PWM avoids disturbing
noises for human beings but might cause problems to animals.

Hallo.
Du brauchst nichts erklären.
Beim LPC ist die PWM Frequenz oscilator/2/256. fix.
Man kann nur den Duty einstellen.