LT3467AIS67 Ver la hoja de datos (PDF) - Linear Technology

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componentes Descripción

Fabricante

LT3467AIS67

1.1A Step-Up DC/DC Converter with Integrated Soft-Start

Linear Technology 

LT3467/LT3467A

APPLICATIONS INFORMATION

Compensation—Theory

Like all other current mode switching regulators, the

LT3467/LT3467A needs to be compensated for stable

and efficient operation. Two feedback loops are used in

the LT3467/LT3467A: a fast current loop which does not

require compensation, and a slower voltage loop which

does. Standard Bode plot analysis can be used to under-

stand and adjust the voltage feedback loop.

As with any feedback loop, identifying the gain and phase

contribution of the various elements in the loop is critical.

Figure 6 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 re-

placed by the equivalent transconductance amplifier gmp.

gmp acts as a current source where the output current is

proportional to the VC voltage. Note that the maximum

output current of gmp is finite due to the current limit

in the IC.

–

gmp

+

VOUT

CPL

RESR RL

VC

RC RO

1.255V

REFERENCE

gma

COUT

R1

CC

R2

3467 F06

CC: COMPENSATION CAPACITOR

COUT: OUTPUT CAPACITOR

CPL: PHASE LEAD CAPACITOR

gma: TRANSCONDUCTANCE AMPLIFIER INSIDE IC

gmp: POWER STAGE TRANSCONDUCTANCE AMPLIFIER

RC: COMPENSATION RESISTOR

RL: OUTPUT RESISTANCE DEFINED AS VOUT DIVIDED BY ILOAD(MAX)

RO: OUTPUT RESISTANCE OF gma

R1, R2: FEEDBACK RESISTOR DIVIDER NETWORK

RESR: OUTPUT CAPACITOR ESR

Figure 6. Boost Converter Equivalent Model

From Figure 6, the DC gain, poles and zeroes can be

calculated as follows:

Output

Pole:

P1=

2

•

π

•

2

RL

•

COUT

Error Amp Pole: P2=

1

2 • π • RO • CC

Error

Amp

Zero:

Z1=

2

•

π

•

1

RC

•

CC

DC

GAIN:

A=

1.255

VOUT 2

•

VIN

• gma

• RO

• gmp

• RL

•

1

2

ESR

Zero:

Z2

=

2

•

π

•

1

RESR

•

COUT

RHP

Zero:

Z3=

2

•

VIN2 • RL

π • VOUT2

•

L

High Frequency Pole: P3> fS

3

Phase

Lead

Zero

:

Z4

=

2

•

π

•

1

R1•

CPL

Phase

Lead

Pole

:

P4

=

2

•

π

•

1

CPL •

R1• R2

R1+ R2

The current mode zero is a right-half plane zero which can

be an issue in feedback control design, but is manageable

with proper external component selection.

3467afe

10

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