NCP3020A 查看數據表（PDF） - ON Semiconductor

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NCP3020A

Synchronous PWM Controller

ON Semiconductor 

NCP3020A, NCP3020B, NCV3020A, NCV3020B

Compensation Type II

This compensation is suitable for electrolytic capacitors.

Components of the Type II (Figure 35) network can be

specified by the following equations:

Figure 35. Type II Compensation

RC1

+

2

@

p @ f0 @ L @ VRAMP @ VOUT

ESR @ VIN @ Vref @ gm

(eq. 40)

CC1

+

0.75

@

2

@

1

p@

fP0

@

RC1

(eq. 41)

CC2

+

p

@

1

RC1

@

fS

(eq. 42)

R1 + VOUT * Vref @ R2

Vref

(eq. 43)

VRAMP is the peak−to−peak voltage of the oscillator ramp

and gm is the transconductance error amplifier gain.

Capacitor CC2 is optional.

Compensation Type III

Tantalum and ceramics capacitors have lower ESR than

electrolytic, so the zero of the output LC filter goes to a

higher frequency above the zero crossover frequency. This

requires a Type III compensation network as shown in

Figure 36.

There are two methods to select the zeros and poles of this

compensation network. Method I is ideal for tantalum

output capacitors, which have a higher ESR than ceramic:

fZ1 + 0.75 @ fP0

(eq. 44)

fZ2 + fP0

(eq. 45)

fP2 + fZ0

(eq. 46)

fP3

+

fS

2

(eq. 47)

Method II is better suited for ceramic capacitors that

typically have the lowest ESR available:

Ǹ fZ2 + f0 @

1 * sinq max

1 ) sin q max

(eq. 48)

Ǹ fP2 + f0 @

1 ) sin q max

1 * sin q max

(eq. 49)

fZ1 + 0.5 @ fZ2

(eq. 50)

fP3 + 0.5 @ fS

(eq. 51)

qmax is the desired maximum phase margin at the zero

crossover frequency, ƒ0. It should be 45° − 75°. Convert

degrees to radians by the formula:

ǒ Ǔ q max + q maxdegress @

2@p

360

: Units + radians

(eq. 52)

The remaining calculations are the same for both methods.

RC1

uu

2

gm

(eq. 53)

CC1

+

2

@

p

@

1

fZ1

@

RC1

(eq. 54)

CC2

+

2

@

p

@

1

fP3

@

RC1

CFB1

+

2

@

p

@

f0

@ L @ VRAMP

VIN @ RC1

@

COUT

(eq. 55)

(eq. 56)

RFB1

+

2p

@

1

CFB1

@

fP2

(eq. 57)

R1

+

2

@

p

@

1

CFB1

@

fZ2

*

RFB1

(eq. 58)

V

R2 +

ref

@ R1

VOUT * Vref

(eq. 59)

If the equation in Equation 60 is not true, then a higher value

of RC1 must be selected.

R1

@

R1

RFB1 )

@ R2

R2 @

@ RFB1

RFB1 )

R1

@

R2

u

1

gm

(eq. 60)

Figure 36. Type III Compensation

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