DocID023635 Rev 2

13/34

AN4158

Phase current control in stepper motor driving

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The back electromotive force (BEMF) is the voltage generated by the rotating magnetic field

of the rotor as an effect of Faraday’s law of induction. Its effect can be modeled as

a sinewave voltage generator with frequency equal to a quarter of the motor full step rate

and amplitude proportional to the rotation speed (see Equation 3).

Equation 3

The BEMF effect on the current control system is to counter the voltage applied by the

power stage limiting the phase current (especially at high speed). In general, as explained in

the following paragraphs, the BEMF voltage may make it more difficult to regulate the

desired current.

The algorithm implemented by the controller determinates the performance of the

application, in particular when microstepping driving is used.

Figure 7. Motor phase electrical model

R

Ph

V

BEMF

L

Ph

Motor phase equivalent circuit

AM15109v1



=

B

4

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=