EVAL6470H Datasheet, PDF (36/70 Pages) STMicroelectronics – dSPIN fully integrated microstepping motor driver with motion engine and SPI

Phase current control
L6470
7.4
BEMF compensation
Using the speed information, a compensation curve is added to the amplitude of the voltage
waveform applied to the motor winding in order to compensate the BEMF variations during
acceleration and deceleration (see Figure 16).
The compensation curve is approximated by a stacked line with a starting slope (ST_SLP)
when speed is lower than a programmable threshold speed (INT_SPEED) and a fine slope
(FN_SLP_ACC and FN_SLP_DEC) when speed is greater than the threshold speed (see
Section 9.1.11, Section 9.1.12, Section 9.1.13 and Section 9.1.14).
Figure 16. BEMF compensation curve
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To obtain different current values during acceleration and deceleration phases, two different
final slope values, and consequently two different compensation curves, can be
programmed.
The acceleration compensation curve is applied when the motor runs. No BEMF
compensation is applied when the motor is stopped.
7.5
Motor supply voltage compensation
The sinewave amplitude generated by the PWM modulators is directly proportional to the
motor supply voltage (V_S). When the motor supply voltage is different from its nominal value,
the motor phases are driven with an incorrect voltage. The L6470 can compensate motor
supply voltage variations in order to avoid this effect.
The motor supply voltage should be connected to the integrated ADC input through a
resistor divider in order to obtain V_REG/2 voltage at the ADCIN pin when V_S is at its nominal
value (see Figure 17).
The ADC input is sampled at f_S frequency, which is equal to PWM frequency.
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