L6470 datasheet(36/70 Pages) STMICROELECTRONICS

36 / 70 page

Phase current control

L6470

36/70

Doc ID16737 Rev 4

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).

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 (VS). 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 VREG/2 voltage at the ADCIN pin when VS is at its nominal

value (see Figure 17).

The ADC input is sampled at fS frequency, which is equal to PWM frequency.

Figure 16.

BEMF compensation curve

L6470 데이터시트(PDF) 36 Page - STMicroelectronics