Datasheet
Phase current control L6480
36/75 DocID023278 Rev 4
7 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. Sine wave amplitude is
proportional to the motor supply voltage multiplied by a coefficient (K
VAL
). K
VAL
ranges from
0 to 100% and the sine wave amplitude can be obtained through the following formula:
Equation 1
Different K
VAL
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 on page 47). KVAL value is
calculated according to the following formula:
Equation 2
where K
VAL_X
is the starting K
VAL
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 on page 40).
7.1 PWM sine wave generators
The two voltage sine waves applied to the stepper motor phases are generated by two
PWM modulators.
The PWM frequency (f
PWM
) is proportional to the oscillator frequency (f
OSC
) 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 F_PWM_INT and F_PWM_DEC parameters in the CONFIG register (see
Table 38 on page 57 and Table 39 on page 57, Section 9.1.23 on page 54).
Available PWM frequencies are listed in Section 9.1.23 on page 54 from Table 40 on
page 58 to Table 43 on page 59.
V
OUT
V
S
K
VAL
=
K
VAL
K
VAL_X
BEMF_COMP+VSCOMP K_THERMmicrost ep=
f
PWM
f
OSC
512 N
------------------ m=