L6480 datasheet(35/73 Pages) STMICROELECTRONICS

35 / 73 page

L6480

Phase current control

Doc ID 023278 Rev 3

35/73

Phase current control

The L6480 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 9.1.10). 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 L6480 offers various methods to guarantee a stable current value, allowing the

compensation of:

●

low speed distortion (Section 7.3)

●

back electromotive force (Section 7.4)

●

motor supply voltage variation (Section 7.5)

●

windings resistance variation (Section 7.6).

7.1

PWM sinewave generators

The two voltage sinewaves applied to the stepper motor phases are generated by two PWM

modulators.

The PWM frequency (fPWM) is proportional to the oscillator frequency (fOSC) and can be

obtained through the following formula:

Equation 3

OUT

VAL

⋅

VAL

VAL_X

BEMF_COMP

() VSCOMP K_THERM

[] microst

PWM

OSC

512

⋅

---------------------

⋅

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