Input Capacitor Selection

( )

( )

f

IN

OUT

OUT

IN min

IN

SW

RIPPLE C

I

V

C

44 F

V

V

´

=

=

m

´

´

(30)

(

)

(

)

IN

IN

RIPPLE ESR _ C

C

OUT

RIPPLE

V

ESR

4.3 m

I

I

2

=

=

W

æ

ö

+

ç

÷

ç

÷

è

ø

(31)

Choosing MOSFETS

High-Side MOSFET Power Loss

(

)

( )

f

2

D1

S1

D2

S2

HFET _ Loss

COND1

SW1

RMS1

IN

SW

DS on 1

I

t

I

t

P

P

P

I

R

V

649 mW

6

2

´

´

æ

ö

=

+

=

´

+

´

+

´

=

ç

÷

è

ø

(32)

Synchronous Rectifier MOSFET Power Loss

( )

f

f

2

SR _ Loss

COND2

COND3

RR

RMS2

O

F

D

SW

RR

IN

SW

DS on 2

1

P

P

P

P

I

R

I

V

t

Q

V

382mW

2

=

+

+

=

´

+

´

´

´

+ ´

´

´

=

é

ù

ë

û

Feedback Loop Compensation

0

OUT

1

f

6.0 kHz

2

L

C

=

=

p ´

´

(34)

Z

OUT

1

f

18.8 kHz

2

ESR

C

=

=

p ´

´

(35)

TPS51113, TPS51163

calculated according to Equation 7 and Equation 8, respectively.

Therefore, two 22-

µF ceramic capacitors with 2-mΩ ESR can meet this requirement.

Equation 13, the total power loss of the high-side MOSFET is estimated.

diode has a 0.84-V diode forward voltage and 15-nC reverse recovery charge. The output driver deadtime is 30

ns. By using Equation 14 through Equation 18, the total power loss of the synchronous MOSFET is estimated,

(33)

Since TPS51113 and TPS51163 utilize voltage-mode control for buck converters, Type III network is

recommended for loop compensation. The converter utilizes a 1.5-

µH inductor and 470-µF capacitor with 18-mΩ

Also, the ESR zero of the buck converter can be achieved by using Equation 20.

18

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