POWERSTEP01 datasheet(38/92 Pages) STMICROELECTRONICS

38 / 92 page

Phase current control: voltage mode

powerSTEP01

38/92

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Phase current control: voltage mode

When the voltage mode driving is selected (CM_VM bit in STEP_MODE register is set to 0),

the powerSTEP01 controls the phase current applying a sinusoidal voltage to motor

windings. Phase current amplitude is not directly controlled but depends on phase voltage

amplitude, load torque, motor electrical characteristics and rotation speed. Sinewave

amplitude is proportional to the motor supply voltage multiplied by a coefficient (KVAL). KVAL

ranges from 0 to 100% and the sinewave amplitude can be obtained through the following

formula:

Equation 1

Different KVAL values can be programmed for acceleration, deceleration and constant speed

phases and when the motor is stopped (HOLD phase) through KVAL_ACC, KVAL_DEC,

KVAL_RUN and KVAL_HOLD registers (Section 11.1.10 on page 56). KVAL value is

calculated according to the following formula:

Equation 2

where KVAL_X is the starting KVAL value programmed for the present motion phase

(KVAL_ACC, KVAL_DEC, KVAL_RUN or KVAL_HOLD), BEMF_COMP is the BEMF

compensation curve value, VSCOMP and K_THERM are the motor supply voltage and

winding resistance compensation factors and microstep is the current microstep value

(fraction of target peak current).

The powerSTEP01 offers various methods to guarantee a stable current value, allowing the

compensation of:



Low speed distortion (Section 8.3)



Back electromotive force (Section 8.4)



Motor supply voltage variation (Section 8.5)



Winding resistance variation (Section 8.6 on page 42)

VOUT

VS KVAL



KVAL

KVAL_X BEMF_COMP

 VSCOMP K_THERM



 microst



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