DocID023491 Rev 3

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AN4144

Voltage mode driving

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The control system generates the phase voltage using a PWM modulation. The outputs

the resulting square-wave is adjusted through its duty cycle (on time over square-wave

period ratio) according to Equation 8:

Equation 8

The duty cycle ranges from 0% (the output is always forced to ground) to 100% (the output

The BEMF compensation curve is implemented adjusting the PWM duty cycle, so all the

voltage values must be normalized to the supply voltage of the power stage (Figure 3).

Figure 3. BEMF compensation curve

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=

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=

V

Speed

[step/s]

Intersect

speed

Kval

Starting

slope

Final

slope

AM12859v1