AN4158 datasheet(13/34 Pages) STMICROELECTRONICS

Teilenummer	AN4158

Bauteilbeschribung	Peak current control with automatic decay adjustment

PDF	34 Pages

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Hersteller	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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13 / 34 page

DocID023635 Rev 2

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AN4158

Phase current control in stepper motor driving

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

BEMF

Motor phase equivalent circuit

AM15109v1

A VBEMF Ke fBEMF



fBEMF

fstep

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AN4158 Datenblatt(PDF) 13 Page - STMicroelectronics