´

³

´

OUT

SW

X

V

ESR

20mV

f

L

£

p ´

´

SW

OUT

f

1

2

ESR C

3

(

)

(

)

(

)

æ

ö

æ

ö

-

ç

÷

´

-

´

´

ç

÷

ç

÷

ç

÷

´

´

è

ø

è

ø

=

IN

OUT

OUT

OCL

DS(on)

X

SW

IN

TRIP

TRIP

V

V

V

8

I

R

2 L

f

V

R

I

(

)

(

)

(

)

(

)

(

)

-

´

´

=

+

´

´

´

IN

OUT

OUT

max

TRIP

TRIP

IND peak

SW

IN

DS on

max

V

V

V

R

I

1

I

8 R

L f

V

(

)

(

)

(

)

(

)

(

)

(

)

(

)

(

)

-

´

-

´

=

´

=

´

´

´

IN

OUT

OUT

IN

OUT

OUT

max

max

X

SW

IN

O

SW

IN

IND ripple

max

max

max

V

V

V

V

V

V

1

3

L

I

f

V

I

f

V

(

)

=

æ

ö

ç

÷

ç

÷

ç

÷ -

´

æ

ö

ç

÷

ç

÷

-

ç

÷

ç

÷

ç

÷

è

ø

è

ø

IND ripple

OUT

R1

R2

1.8

1

I

ESR

V

2

TPS51916

SLUSAE1D – DECEMBER 2010 – REVISED JUNE 2012

www.ti.com

External Components Selection

The external components selection is simple in D-CAP™ mode.

1. DETERMINE THE VALUE OF R1 AND R2

The output voltage is determined by the value of the voltage-divider resistor, R1 and R2 as shown in Figure 35.

R1 is connected between VREF and REFIN pins, and R2 is connected between the REFIN pin and GND. Setting

R1 as 10-k

Ω is a good starting point. Determine R2 using Equation 7.

(7)

2. CHOOSE THE INDUCTOR

The inductance value should be determined to yield a ripple current of approximately ¼ to ½ of maximum output

current. Larger ripple current increases output ripple voltage and improves the signal-to-noise ratio and helps

stable operation.

(8)

The inductor needs a low direct current resistance (DCR) to achieve good efficiency, as well as enough room

above peak inductor current before saturation. The peak inductor current can be estimated in Equation 9.

(9)

(10)

4. CHOOSE THE OUTPUT CAPACITORS

D-CAP™ Mode

Organic semiconductor capacitor(s) or specialty polymer capacitor(s) are recommended. Determine ESR to meet

small signal stability and recommended ripple voltage. A quick reference is shown in Equation 11 and

Equation 12.

(11)

(12)

D-CAP2™ Mode

Determine output capacitance to meet small signal stability as shown in Equation 13.

22

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