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PWM MODULATOR RELATIONSHIPS

MODULATOR GAIN

vs

SWITCHING FREQUENCY

100

1 k

10 k

100 k

ESR Zero, + 1

LC Filter, - 2

Resultant, - 1

GAIN

180°

−90°

−270°

PHASE

+ 1

− 1

− 1

0 dB

UDG−02189

+

R1

R3

C3

C2

(optional)

C1

R2

7

8

VREF

COMP

VFB

1

2p

R2

C1

(Hz)

1

2p

R1

C3

(Hz)

(25)

1

2p

R2

C2

(Hz)

1

2p

R3

C3

(Hz)

1

2p

R1

C2

G

(Hertz)

(26)

TPS40060

TPS40061

SLUS543D–DECEMBER 2002–REVISED SEPTEMBER 2004

APPLICATION INFORMATION (continued)

Figure 8.

Figure 9.

Figure 10. Type III Compensation of Configuration

Figure 11. Type III Compensation Gain and Phase

The poles and zeros for a type III network are described in Equation 25.

The value of R1 is somewhat arbitraty, but influences other component values. A value between 50kΩ and

100kΩ usually yields reasonable values.

The unity gain frequency is described in Equation 26.

16