L6472 datasheet(35/69 Pages) STMICROELECTRONICS

35 / 69 page

L6472

Phase current control

Doc ID 022729 Rev 1

35/69

7.2

Auto-adjusted decay mode

During the current control, the device automatically selects the better decay mode in order

to follow the current profile reducing the current ripple.

At reset, the OFF time is performed by turning on both the low-side MOSFETs of the power

stage and the current recirculates in the lower half of the bridge (slow decay).

If, during a PWM cycle, the target current threshold is reached in a time shorter than the

TON_MIN value, a fast decay of TOFF_FAST/8 (T_FAST register) is immediately performed

turning on the opposite MOS of both half bridges and the current recirculates back to the

supply bus.

After this time, the bridge returns to the ON state: if the time needed to reach the target

current value is still less than TON_MIN, a new fast decay is performed with a period twice

the previous one. Otherwise, the normal control sequence is followed as described in

Section 7.1. The maximum fast decay duration is set by the TOFF_FAST value.

Figure 17.

Adaptive decay - fast decay tuning

When two or more fast decays are performed with the present target current, the control

system adds a fast decay at the end of every OFF time, keeping the OFF state duration

constant (tOFF is split into tOFF,SLOW and tOFF,FAST). When the current threshold is increased

by a microstep change (rising step), the system returns to normal decay mode (slow decay

only) and the tFAST value is halved.

Stopping the motor or reaching the current sinewave zero crossing causes the current

control system to return to the reset state.

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