Datasheet

DocID023278 Rev 4 37/75
L6480 Phase current control
75
7.2 Sensorless stall detection
The L6480 is able to detect a motor stall caused by an excessive load torque. When the
motor is driven using the voltage mode approach, a stall condition corresponds to an
unexpected increase of the phase current. Imposing a current threshold slightly above the
operative current, it is possible to detect the stall condition without speed or position
sensors.
The L6480 measures the load current of each phase sensing the V
DS
voltage of the low-
side Power MOSFETs. When any of the V
DS
voltages rise over the programmed threshold,
the STEP_LOSS_X flag in the STATUS register of the respective bridge (STEP_LOSS_A or
STEP_LOSS_B) is forced low. The failure flag is kept low until the V
DS
voltages fall below
the programmed threshold and a GetStatus command is sent to the device (Section 9.1.24
on page 59 and Section 9.2.20 on page 71).
The stall detection threshold can be programmed in one of 32 available values ranging from
31.25 mV to 1 V with steps of 31.25 mV (see Section 9.1.18 on page 50).
Stall detection comparators are disabled, in order to avoid wrong voltage measurements, in
the following cases:
 The respective half-bridge is in high impedance state (both MOSFETs forced off)
 The respective half-bridge is commutating
 The respective half-bridge is commutated and the programmed blanking time has not
yet elapsed
 The respective low-side gate is turned off.
7.3 Low speed optimization
When the motor is driven at a very low speed using a small driving voltage, the resulting
phase current can be distorted. As a consequence, the motor position is different from the
ideal one (see Figure 16).
The device implements a low speed optimization in order to remove this effect.