L6986H datasheet(37/68 Pages) STMICROELECTRONICS

部品番号	L6986H

部品情報	38 V, 2 A synchronous step-down switching regulator with 30 μA quiescent current

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メーカー	STMICROELECTRONICS [STMicroelectronics]

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whereas the zero is defined as:

fZ= 1

2⋅π⋅Rc⋅Cc

(27)

5.3

Voltage divider

The contribution of the internal voltage divider for fixed output voltage devices is:

GDIV(s)= R2R1+R2= VFBVOUT=0.853.3=0.2575 L6986H3V

GDIV(s)= R2R1+R2= VFBVOUT=0.855=0.17 L698H5V

(28)

while for the adjustable output part number L6986H is:

GDIV(s)= R2R1+R2 L6986H

(29)

A small signal capacitor in parallel to the upper resistor (see Figure 37. Leading network example) of the voltage

divider implements a leading network (fzero < fpole), sometimes necessary to improve the system phase margin:

Figure 37. Leading network example

L6986H

Power GND

signal GND

Cr1

uC RST

RST

VCC

SS/INH

SYNCH

FSW

MLF

COMP

DELAY

SGND

PGND PGND

VIN

VBIAS

GND

VIN

VOUT

The Laplace transformer of the leading network is:

GDIV(s)= R2R1+R2⋅ (1+s+R1⋅CR1)

(1+s⋅ R1⋅R2

R1+R2⋅CR1)

(30)

where

fZ= 1

2⋅π⋅R1⋅CR1

fp= 1

2⋅π⋅ R1⋅R2

R1+R2⋅CR1

fZ<fp

(31)

L6986H

Voltage divider

DS12905 - Rev 2

page 37/68

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