L6983 datasheet(28/63 Pages) STMICROELECTRONICS

No de pièce	L6983

Description	38 V, 3 A synchronous step-down converter with 17 μA quiescent current

PDF	63 Pages

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Fabricant	STMICROELECTRONICS [STMicroelectronics]

Site Internet	http://www.st.com

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fPLF= 1

2∙π∙RO∙CC

(19)

fPHF= 1

2∙π∙RO∙CO

(20)

Whereas the zero is defined as:

fZ= 1

2∙π∙RC∙CC

(21)

7.3

Voltage divider

The contribution of a simple voltage divider is:

GDIVs = R2R1+R2

(22)

A small signal capacitor in parallel to the upper resistor (only for the adjustable part number) of the voltage divider

implements a leading network (fZERO < fPOLE), sometimes necessary to improve the system phase margin:

Figure 25. Leading network example

PGOOD

BOOT

VBIAS

VOUT/FB

PGND

VIN

VINLDO

EN/CLKIN

FSW

VCC

A GND

E.P.

L6983

VOUT

GND

VIN

RFSW

CVCC

CBOOT

RPGOOD

COUT

CIN

CR1

CFILT

RFILT

Laplace transformer of the leading network:

GDIVs = R2R1+R2∙ 1+s∙R1∙CR1

1+s∙ R1∙R2

R1+R2∙CR1

(23)

where:

fZ= 1

2∙π∙R1∙CR1

(24)

fP= 1

2∙π∙ R1∙R2

R1+R2∙CR1

(25)

fZ<fP

(26)

So closing the loop, the loop gain is:

Gs =GDIVs ∙GCOs ∙AOs

(27)

L6983

Voltage divider

DS13116 - Rev 1

page 28/63

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