DocID023635 Rev 2

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AN4158

STMicroelectronics enhanced current control

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Figure 18. Decay strategy change due to second on-time threshold violation



At the first occurrence of the minimum on-time violation, the fast decay duration is set



If a further minimum on-time violation occurs, a new fast decay is used with double the



(except if a current reference change occurred, see Section 4.1.1).

decay phase when the slow and fast decay combination is used. Figure 19 shows an

example of the system operation.

Figure 19. Fast decay time regulation

4.1.1

Rising and falling steps (reference current changes)

In microstepping operation the current reference changes according to the point of the

current sinewave which must be obtained.

When the reference value is changed, there are two cases:

1.

The reference current is increased. This event is called “rising step”.

2.

The reference current is reduced. This event is called “falling step”.

These events are managed by the L6472 and L6474 current control, as follows.

In the case of rising step the phase is immediately turned on regardless of the control cycle

t

ON_MIN

t

ON_MIN

t

t

t

on

t

on

t

fast

t

t

The second violation causes the control system

to change the decay strategy.

A slow decay followed by a fast decay are used

from now, until the change of the reference current.

First minimum on-time violation.

Fast decay is used.

t

ON_MIN

t

ON_MIN

t

on

OFF

t

on

t

fast

t

fast

System returns to normal

operation (slow decay)

t

Second minimum

on-time violation.

Fast decay is used.

Reference current

AM15120v1

t

ON_MIN

t

ON_MIN

t

ON_MIN

t

t

t

on

t

on

t

on

t

t

fast

t

fast

t

fast

t

slow + fast decay strategy

with t

t

t

Reference current

AM15121v1