DocID025240 Rev 2

21/25

AN4355

Stall detection (L6480 only)

25

6

Stall detection (L6480 only)

The L6480 device also includes a sensorless stall detection system. This feature allows the

device to detect the stall condition of the motor measuring the increase of the phase current

caused by the sudden cancellation of the back electromotive force.

The voltage mode control applies a sinusoidal voltage to the motor phases obtaining

a sinusoidal current. The amplitude of the voltage sine wave is increased with speed in

order to compensate the back electromotive force effect and keep the amplitude of the

phase current constant. If the motor stalls (i.e.: stops its rotation) the back electromotive

force becomes null, but the voltage applied to the phase is still increased to face its effect. In

this condition the phase current results higher than the nominal one and the stall condition

can be easily detected. The load current is measured monitoring the drain-source voltage

drop of the low-side external power MOSFETs.

The stall detection threshold must be set above the nominal peak current.

Figure 15. Stall detection threshold

The relation between the voltage threshold which is programmed into the device register

and the actual load current is defined by the following formula:

Equation 2

temperature of the power stage must be considered when the threshold value is defined.