DocID023635 Rev 2

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AN4158

Setup and optimization

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Figure 26. Falling step - 8 microstep example

In parameter dimensioning the microstepping resolution of the system should be

considered; the higher the resolution, the shorter the fast step time. In fact, the drop

between subsequent microsteps decreases with the resolution.

Long FAST_STEP timings may cause deep undershoots in the first part of the negative

slope of the sinewave, but give better performance in the final part where the drop between

the microsteps is higher (see Figure 27).

Short FAST_STEP timings fit better to the drops of the first falling steps, but require a longer

fast decay sequence in the final part of the negative slope of the sinewave, causing more

commutations (see Figure 28).

The optimal trade-off between the starting and the final part of the negative slope requires

a fine tuning.

In any case, the minimum fast decay (one-fourth of FAST_STEP) must be longer than

TON_MIN to avoid subsequent minimum on-time violations.

At the beginning of the negative slope of

the sinewave a shorter fast decay is required

.

At the end of the negative slope of

the sinewave a longer fast decay is required.

In the last falling step the system forces

a zero current disabling the power bridge.

The falling step algorithm is not used

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AM15130v1