L6472 datasheet(33/69 Pages) STMICROELECTRONICS

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L6472

Phase current control

Doc ID 022729 Rev 1

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Phase current control

The L6472 performs a new current control technique, named predictive current control,

allowing the device to obtain the target average phase current. This method is described in

detail in Section 7.1. Furthermore, the L6472 automatically selects the better decay mode in

order to follow the current profile.

Current control algorithm parameters can be programmed by the T_FAST, TON_MIN,

TOFF_MIN and CONFIG registers (see Section 9.1.11, 9.1.12, 9.1.13 and 9.1.18 for

details).

Different current amplitude can be set for acceleration, deceleration and constant speed

phases and when the motor is stopped through the TVAL_ACC, TVAL_DEC, TVAL_RUN

and TVAL_HOLD registers (see Section 7.4). The output current amplitude can also be

regulated by the ADCIN voltage value (see Section 6.15).

Each bridge is driven by an independent control system that shares the control parameters

only with other bridges.

7.1

Predictive current control

Unlike a classical peak current control system, that causes the phase current decay when

the target value is reached, this new method keeps the power bridge on for an extra time

after reaching the current threshold.

At each cycle the system measures the time required to reach the target current (tSENSE).

After that the power stage is kept in a “predictive” ON state (tPRED) for a time equal to the

mean value of tSENSE in the last two control cycles (actual one and previous one), as shown

in Figure 15.

Figure 15.

Predictive current control

At the end of the predictive ON state the power stage is set in the OFF state for a fixed time,

as in a constant tOFF current control. During the OFF state both slow and fast decay can be

performed; the better decay combination is automatically selected by the L6472, as

described in Section 7.2.

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