LT3579IUFD-1-PBF(RevA) 데이터 시트보기 (PDF) - Linear Technology

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LT3579IUFD-1-PBF
(Rev.:RevA)

6A Boost/Inverting DC/DC Converter with Fault Protection

Linear Technology 

LT3579/LT3579-1

APPENDIX

As with any feedback loop, identifying the gain and phase

contribution of the various elements in the loop is critical.

Figure 18 shows the key equivalent elements of a boost

converter. Because of the fast current control loop, the

power stage of the IC, inductor and diode have been replaced

by a combination of the equivalent transconductance

amplifier gmp and the current controlled current source

(which converts IVIN to

ηVIN

VOUT

IVIN

).

Gmp

acts

as

a

current

source where the peak input current, IVIN, is proportional

to the VC voltage.

–

gmp

+

IVIN

η • VIN

VOUT

•

IVIN

1.215V

REFERENCE

VOUT

RESR RL

COUT

CPL R1

gma

CF RC RO

CC

R2

FB

R2

35791 F18

CC: COMPENSATION CAPACITOR

COUT: OUTPUT CAPACITOR

CPL: PHASE LEAD CAPACITOR

CF: HIGH FREQUENCY FILTER CAPACITOR

gma: TRANSCONDUCTOR AMPLIFIER INSIDE IC

gmp: POWER STAGE TRANSCONDUCTANCE AMPLIFIER

RC: COMPENSATION RESISTOR

RL: OUTPUT RESISTANCE DEFINED AS VOUT/ILOADMAX

RO: OUTPUT RESISTANCE OF gma

R1, R2; FEEDBACK RESISTOR DIVIDER NETWORK

RESR: OUTPUT CAPACITOR ESR

η: CONVERTER EFFICIENCY (~90% AT HIGHER CURRENTS)

Figure 18. Boost Converter Equivalent Model

From Figure 18, the DC gain, poles and zeros can be

calculated as follows:

DC Gain:

ADC

=

gma

•RO •gmp • η•

VIN

VOUT

•

RL

2

•

0.5R2

R1 + 0.5R2

Output

Pole:

P1 =

2

2• π •RL

• COUT

Error

Amp

Pole:

P2

=

1

2• π•(RO +RC )•CC

Error

Amp

Zero:

Z1 =

1

2• π •RC

•CC

ESR

Zero:

Z2

=

1

2• π •RESR

• COUT

RHP

Zero:

Z3

=

VIN 2•RL

2• π • VOUT 2•L

High Frequency Pole: P3> fS

3

Phase Lead Zero: Z4 =

1

2• π •R1•CPL

Phase

Lead Pole: P4

=

1

2•

π

•

R1 • 0.5R2

R1 + 0.5R2

•CPL

Error Amp Filter Pole:

P5

=

2•

π

•

1

RC •RO

RC +RO

CF

,

CF

<

CC

10

Note that the maximum output currents of gmp and gma

are finite. The output of the gmp stage is limited by the

minimum switch current limit (see Electrical Specifications)

and gma is nominally limited to about ±12μA.

30

For more information www.linear.com/LT3579

35791fa

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