AN4158 datasheet(16/34 Pages) STMICROELECTRONICS

Part #	AN4158

Description	Peak current control with automatic decay adjustment

PDF	34 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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16 / 34 page

Peak current control with PWM and constant off-time

AN4158

16/34

DocID023635 Rev 2

When the slow decay is not able to decrease the phase current, the fast decay method can

be used. The fast decay forces the current reduction applying the supply voltage in reverse

direction. This way the current is actively reduced using the same voltage used to force it

into the phase during the on-time.

In this case the current drop and then the ripple are greater than with slow decay, but the

peak current is kept under control (see Equation 7).

Equation 7

Figure 10. Back electromotive force limiting the slow decay effectiveness

BEMF

Motor phase equivalent circuit

BEMF >> IPh x RPh

BEMF < 0

AM15112v1

I

RPh IPh VBUS



 L

Ph tOFF





AN4158 Datasheet(PDF) 16 Page - STMicroelectronics