MPZ2012S221A datasheet(29/56 Pages) STMICROELECTRONICS

Il numero della parte	MPZ2012S221A

Spiegazioni elettronici	38 V, 10 W synchronous iso-buck converter for isolated applications

PDF	56 Pages

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Produttore elettronici	STMICROELECTRONICS [STMicroelectronics]

Homepage	http://www.st.com

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AOs =

AVO∙ 1+s∙RC∙CC

s2∙RO∙CO∙RC∙CC+s∙ RO∙CC+RO∙CO+RC∙CC +1

(11)

where:

AVO=Gm∙RO

(12)

The poles of this transfer function are (if CC >> CO):

fPLF= 1

2∙π∙RO∙CC

(13)

fPHF= 1

2∙π∙RO∙CO

(14)

Whereas the zero is defined as:

fZ= 1

2∙π∙RC∙CC

(15)

8.3

Voltage divider

The contribution of a simple voltage divider is:

GDIVs = R2R1+R2

(16)

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 36. Contribution of the resistor divider

VIN

VINLDO

EN/CLKIN

FSW

VCC

AGND

PGOOD

BOOT

VBIAS

PGND

VIN

GND

VOUT_prim

VOUT_iso

GND_iso

L6983I

CIN

CLDO

RLDO

RFSW1

CVCC

RFB1

RFB2

CSEC

COUT

CFF

Laplace transformer of the leading network:

G_DIV s = R2R1+R2∙ 1+s∙R_1∙C_R1 / 1+s∙R1∙R2

R1+R2 ∙C_R1

(17)

where:

fz= 1

2∙π∙R1∙CR1

(18)

L6983I

Voltage divider

DS14040 - Rev 1

page 29/56

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