AN4158 datasheet(17/34 Pages) STMICROELECTRONICS

tên linh kiện	AN4158

Giải thích chi tiết về linh kiện	Peak current control with automatic decay adjustment

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DocID023635 Rev 2

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AN4158

Peak current control with PWM and constant off-time

Both decay methods have pros and cons: the slow decay allows a lower current ripple to be

obtained, but at low current values or at high speed (significant BEMF value) the current

control may fail. The fast decay, on the other hand, keeps the current under control at the

cost of a higher ripple.

3.2

Minimum on-time limit

The control system, according to its structure, is usually not able to check the phase current

immediately after the beginning of the on-phase (usually a blanking time is adopted to avoid

spurious triggering of the current comparator), as shown in Figure 12. This limits the

minimum on-time the power bridge must remain in the on-phase. The minimum current

increase related to the tcomm can be estimated through Equation 8 (back electromotive force

has not been taken into account for simplicity).

Figure 11. Constant off-time control using fast decay

BUS

Sense

SHUNT

BUS

Sense

SHUNT

BUS

Sense

Ref

Peak

OFF

AM15113v1

AN4158 bảng dữ liệu(PDF) 17 Page - STMicroelectronics