IRU3046CF datasheet(10/20 Pages) IRF

Part #	IRU3046CF

Description	DUAL SYNCHRONOUS PWM CONTROLLER WITH CURRENT SHARING CIRCUITRY AND LDO CONTROLLER

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Manufacturer	IRF [International Rectifier]

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10 / 20 page

10

Rev. 1.9

09/27/02

IRU3046

www.irf.com

The pole sets to one half of switching frequency which

results in the capacitor CPOLE:

For a general solution for unconditionally stability for any

type of output capacitors, in a wide range of ESR values

we should implement local feedback with a compensa-

tion network. The typically used compensation network

for voltage-mode controller is shown in Figure 7.

Figure 7 - Compensation network with local

feedback and its asymptotic gain plot.

In such configuration, the transfer function is given by:

The error amplifier gain is independent of the transcon-

ductance under the following condition:

By replacing ZIN and Zf according to figure 7, the trans-

former function can be expressed as:

Ve

1 -

gmZf

1 +

gmZIN

VOUT

=

As known, transconductance amplifier has high imped-

ance (current source) output, therefore, consider should

be taken when loading the E/A output. It may exceed its

source/sink output current capability, so that the ampli-

fier will not be able to swing its output voltage over the

necessary range.

The compensation network has three poles and two ze-

ros and they are expressed as follows:

Cross Over Frequency:

The stability requirement will be satisfied by placing the

poles and zeros of the compensation network according

to following design rules. The consideration has been

taken to satisfy condition (15) regarding transconduc-

tance error amplifier.

1)

Select the crossover frequency:

2)

Select R7, so that R7 >>

3)

Place first zero before LC’s resonant frequency pole.

2

gm

Fo < FESR and Fo

[ (1/10 ~ 1/6)3 fS

FZ1

≅ 75% FLC

C11 =

1

2

p 3 FZ1 3 R7

CPOLE =

≅

p 3 R4 3 fS - 1

C9

1

p 3 R4 3 fS

For FP <<

fS

2

FP1 = 0

1

2

p3C103(R6 + R8)

FZ2 =

≅

1

2

p3C103R6

FZ1 =

1

2

p3R73C11

FP3 =

≅

1

2

p3R73

FP2 =

1

2

p3R83C10

1

2

p3R73C12

C12

3C11

C12+C11

(

)

VOUT

VREF

R5

R6

R8

C10

C12

C11

R7

Ve

FZ1

FZ2

FP2

FP3

E/A1

Zf

ZIN

Frequency

Gain(dB)

H(s) dB

Comp1

Fb1

gmZf >> 1

and

gmZIN >>1

---(15)

H(s)=

sR6(C12+C11)

1+sR7

3(1+sR8C10)

1

(1+sR7C11)

3[1+sC10(R6+R8)]

3

[

(

)]

C12C11

C12+C11

Where:

VIN = Maximum Input Voltage

VOSC = Oscillator Ramp Voltage

Lo = Output Inductor

Co = Total Output Capacitors

FO1 = R7

3C103

3

---(16)

VIN

VOSC

1

2

p3Lo3Co

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