L6480 datasheet(36/73 Pages) STMICROELECTRONICS

36 / 73 page

Phase current control

L6480

36/73

Doc ID 023278 Rev 3

'N' is the integer division factor and 'm' is the multiplication factor. 'N' and 'm' values can be

programmed by F_PWM_INT and F_PWM_DEC parameters in the CONFIG register (see

Table 38 and Table 39, Section 9.1.23).

Available PWM frequencies are listed in Section 9.1.23 from Table 40 to Table 43.

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 VDS voltage of the low-

side Power MOSFETs. When any of the VDS 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 VDS voltages fall below

the programmed threshold and a GetStatus command is sent to the device (Section 9.1.24

and Section 9.2.20).

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).

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 gates 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.

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