FB

IN

m

COMP

OUT

OUT

C

O

SEN

V

V

1

1

| T |

G

R

1

V

V

2

f

C

A R

=

´

´

´

´

´

=

p ´

´

´

R

C

f

f

5

£

COMP

COMP2

P2

COMP

COMP2

COMP

C

C

C

C

R

+

w

=

´

´

FBB

m

FBB

FBT

P1

COMP

COMP2

R

G

R

R

C

C

´

+

w

=

+

Z1

COMP

COMP

1

C

R

w

=

´

P1

Z1

VA

P2

s

1

G

(s)

s

s 1

æ

ö

w

+

ç

÷

w

è

ø

=

æ

ö

+

ç

÷

w

è

ø

(

)

n

C

1

1

Q

M

1 D

1

0.5

M

=

é

ù

æ

ö

p ´

-

´

+

-

ê

ú

ç

÷

ê

ú

è

ø

ë

û

24

LM3017

SNOSC66D – MARCH 2012 – REVISED SEPTEMBER 2016

www.ti.com

Product Folder Links: LM3017

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Copyright © 2012–2016, Texas Instruments Incorporated

The sampling double pole quality factor is Equation 46.

(46)

The sampling double corner frequency is Equation 47.

ωn = π × fS

(47)

The natural inductor current slope is Equation 48.

M1 = RSEN × VIN / L

(48)

The external ramp slope is Equation 49.

MC = (VSL + ΔVSL) × fS

(49)

A step-up converter produces an undesirable right-half plane zero in the regulation feedback loop. This requires

compensating the regulator such that the crossover frequency occurs well below the frequency of the right-half

plane zero

8.2.2.13.1

Compensation Network Components Calculations

As shown in Figure 25, the LM3017 uses a compensation network base on a transconductance amplifier. The

closed-loop transfer function is defined with Equation 50 through Equation 54.

T(s) = GVA(s) × GVC(s)

where

•

GVA(s) is the transfer function implemented by the compensation network

(50)

(51)

(52)

(53)

(54)

To stabilize the regulator, ensure that the regulator crossover frequency is less than or equal to one-fifth of the

right-half plane zero with Equation 55.

(55)

To determine the crossover frequency it is important to note that, at that frequency, the compensation impedance

(ZCOMP) is dominated by a resistor, and the output impedance (ZOUT) is dominated by the impedance of an output

capacitor. Therefore, when solving for the crossover frequency, the equation (by definition of the crossover

frequency) of the loop gain is simplified to Equation 56.

where

•

|T| is the loop gain magnitude

•

VFB is feedback voltage, 1.275 V

•

VOUT is the output voltage

•

VIN is the input voltage