Main clock source

AN4355

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DocID025240 Rev 2

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Main clock source

The motion engine integrated into the L648x generates the internal step clock starting from

the main clock source of the system. As a consequence, the perturbations on the main clock

affect the accuracy with which the device generates the speed of the motor (step rate).

The main clock also affects the following parameters:



Gate driving timings (controlled current time, boost time, deadtime and blanking time).



Frequency of the PWM modulators (L6480).



On time measurement and current control timings (L6482).

The devices can operate with both external and internal clock sources. By default the clock

source is the integrated oscillator operating at 16 MHz. This solution, if compared to a high

precision external source, allows the maximum integration with lower precision of the

generation of the speed profile (acceleration, deceleration and target speed). The effects on

the current control systems (voltage mode or advanced current control) are negligible.

The device can be configured to use an external clock source or to drive a crystal/resonator.

In both cases the clock frequency must be chosen between four values: 8, 16, 24 or 32

MHz.

Warning:

Setting the wrong value or applying a clock frequency

significantly different from the nominal value might cause

failures.

The external clock source allows obtaining higher precision of the speed profile.