´

³

´

OUT

SW

X

V

ESR

20 mV

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

IND peak

X

SW

IN

DS on

max

V

V

V

V

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

TPS51216

www.ti.com

SLUSAB9A – NOVEMBER 2010 – REVISED APRIL 2013

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 30. 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 6.

(6)

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.

(7)

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 8.

(8)

3. CHOOSE THE OCL SETTING RESISTANCE, RTRIP

Combining Equation 4 and Equation 5, RTRIP can be obtained using Equation 9.

(9)

4. CHOOSE THE OUTPUT CAPACITORS

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 10 and

Equation 11.

(10)

(11)

Copyright © 2010–2013, Texas Instruments Incorporated

Submit Documentation Feedback

21

Product Folder Links :TPS51216