L6470HTR View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
L6470HTR
STMicroelectronics
'L6470HTR' PDF : 70 Pages View PDF
Phase current control
7
Phase current control
L6470
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
VOUT = VS KVAL
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 on page 44). KVAL value is
calculated according to the following formula:
Equation 2
KVAL = KVAL_X + BEMF_COMP VSCOMP K_THERM microstep
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 device offers various methods to guarantee a stable current value, allowing the
compensation of:
low speed optimization (Section 7.3)
back electromotive force value (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
fPWM = 5----f1-O--2--S----C--N--- m
'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 on page 52 and Table 29 on page 52, Section 9.1.21 on page 49).
Available PWM frequencies are listed in Section 9.1.21 from Table 30 on page 53 to
Table 33 on page 54.
34/73
DocID16737 Rev 7
Share Link: 