L6470PD datasheet(34/70 Pages) STMICROELECTRONICS

34 / 70 page

Phase current control

L6470

34/70

Doc ID16737 Rev 5

Phase current control

The L6470 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 the KVAL_ACC, KVAL_DEC,

KVAL_RUN and KVAL_HOLD registers (see 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 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 L6470 offers various methods to guarantee a stable current value, allowing the

compensation of:

●

low speed optimization (Section 7.3 7.3)

●

back electromotive force value (Section 7.4 7.4)

●

motor supply voltage variation (Section 7.5 7.5)

●

windings resistance variation (Section 7.67.6).

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

'N' is the integer division factor and 'm' is the multiplication factor. 'N' and 'm' values can be

programmed by the F_PWM_INT and F_PWM_DEC parameters in the CONFIG register

(see Table 28 and Table 29, Section 9.1.21).

Available PWM frequencies are listed in Section 9.1.21 from Table 30 to Table 33.

OUT

VAL

⋅

VAL

VAL_X

BEMF_COMP

() VSCOMP K_THERM

[] microstep

PWM

OSC

512

⋅

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⋅

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