ADPL21610ECPZ datasheet(9/15 Pages) AD

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Compensation—Theory

Like all other current-mode switching regulators, the

ADPL21610 needs to be compensated for stable and

efficient operation. Two feedback loops are used in

the ADPL21610: a fast current loop, which does not

require compensation, and a slower voltage loop,

which does. Standard Bode plot analysis can be used

to understand 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 12 shows the key equivalent ele-

ments of a boost converter. Because of the fast current

control loop, the power stage of the IC, inductor and

diode have been replaced by the equivalent transcon-

ductance amplifier gmp. gmp acts as a current source

where the output current is proportional to the VC volt-

age. Note that the maximum output current of the gmp

is finite due to the current limit in the IC.

From Figure 12, the DC gain, poles and zeroes can be

calculated as follows:

Output Pole: P1 =

2 x � x RL x COUT

Error Amp Pole: P2 =

2 x � x R0 x CC

Error Amp Zero: Z1 =

2 x � x RC x CC

x VIN x gma x R0 x gmp x RL x

ESR Zero: Z2 =

2 x � x RESR x COUT

2 x � x R1 x CPL

RHP Zero: Z3 =

VIN2 x RL

2 x � x VOUT2 x L

Phase Lead Zero: Z4 =

2 x � x CPL x

Phase Lead Pole: P4 =

DC GAIN: A = 1.255

VOUT2

R1 x R2

R1 + R2

P3 >

High Frequency Pole:

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.

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Analog Devices │ 9

ADPL21610

1.1A Step-Up DC/DC

Converter with Integrated Soft-Start

Figure 12. Boost Converter Equivalent Model

–

gma

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

COUT

CPL

RESR

VOUT

gmp

1.255V

REFERENCE

ADPL21610ECPZ Datasheet(PDF) 9 Page - Analog Devices

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