MCR03EZPFX1002 datasheet(24/36 Pages) IRF

24 / 36 page

IR3837MPbF

Rev 1.31

The transfer function (V

e/Vout) is given by:

The (s) indicates that the transfer function varies

as a function of frequency. This configuration

introduces a gain and zero, expressed by:

First select the desired zero-crossover frequency

o):

Use the following equation to calculate R3:

Where:

in = Maximum Input Voltage

osc = Amplitude of the oscillator Ramp Voltage

o = Crossover Frequency

ESR = Zero Frequency of the Output Capacitor

LC = Resonant Frequency of the Output Filter

8 = Feedback Resistor

To cancel one of the LC filter poles, place the

zero before the LC filter resonant frequency pole:

Use equations (20), (21) and (22) to calculate

C4.

One more capacitor is sometimes added in

parallel with C4 and R3. This introduces one

more pole which is mainly used to suppress the

switching noise.

(18)

.....

)

(

out













(20)

........

..........

(19)

.........

..........

.........

z 





(21)

1/10

1/5

and

.......

ESR





(22)

.......

..........

ESR

osc



The additional pole is given by:

The pole sets to one half of the switching

frequency which results in the capacitor C

POLE:

For a general solution for unconditional stability

for any type of output capacitors, and a wide

range of ESR values, we should implement local

feedback with a type III compensation network.

The typically used compensation network for

voltage-mode controller is shown in figure 20.

(23)

.......

..........



...(24)

..........

POLE





(25)

..........

POLE







Fig.20. Type III Compensation network and

its asymptotic gain plot

VOUT

VREF

E/A

ZIN

Frequency

Gain (dB)

|H(s)| dB

Comp

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