VOUT

VC

gm ps

VOUT

VC

gm ps

fp

fz

Adc

s

1+

2

z

VOUT

= Adc

VC

s

1+

2

p

æ

ö

ç

÷

´ ¦

è

ø

´

æ

ö

ç

÷

´ ¦

è

ø

p

p

ps

L

Adc = gm

R

´

O

L

1

p =

C

R

2

¦

´

´

p

O

ESR

1

z =

C

R

2

¦

´

´

p

TPS54821

SLVSB14

– OCTOBER 2011

www.ti.com

Figure 26. Simplified Small Signal Model for Peak Current Mode Control

Figure 27. Simplified Frequency Response for Peak Current Mode Control

(10)

(11)

(12)

(13)

Where

Small Signal Model for Frequency Compensation

The device uses a transconductance amplifier for the error amplifier and readily supports two of the commonly

used Type II compensation circuits and a Type III frequency compensation circuit, as shown in Figure 28. In

Type 2A, one additional high frequency pole, C6, is added to attenuate high frequency noise. In Type III, one

additional capacitor, C11, is added to provide a phase boost at the crossover frequency. See Designing Type III

Compensation for Current Mode Step-Down Converters (SLVA352) for a complete explanation of Type III

compensation.

18

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