ADP3050

–11–

REV. 0

2. Decide what type of capacitor to use (tantalum, ceramic,

etc.), then look at the table for some possible devices. Many

more values, sizes, and voltage ratings are available, so contact

each manufacturer for a complete product list. If a certain type

of capacitor must be used and space permits, simply use

several devices in parallel to reduce the total ESR.

3. Check the capacitor voltage rating and ripple current rating

to ensure it will work for your application (these ratings are

derated for higher temperatures, so always check the

manufacturer’s data sheet).

4. Make sure the final choice for the output capacitor has been

optimized for cost, size, availability, and performance while

still meeting the required capacitance. The recommended

capacitance is in the 47

µF to 220 µF range.

CATCH DIODE SELECTION

The recommended catch diode is a type 1N5818 Schottky or an

equivalent. The low forward voltage drop (450 mV typical at 1 A)

and fast switching speed of a Schottky rectifier provide the best

performance and efficiency. The 1N5818 is rated at 30 V reverse

voltage and 1 A average forward current. For lower input voltages,

use a lower voltage Schottky to reduce the diode forward voltage

drop and increase overall system efficiency (i.e., a 12 V to 5 V

system does not need a 30 V diode). For automotive applications,

a 60 V Schottky may be necessary. The average forward current for

the catch diode can be calculated by:

II

VV

V

DIODE

OUT

IN

OUT

IN

(AVG)

–

=×

(5)

For the earlier continuous mode example (12 V to 5 V at 800 mA),

the average diode current would be:

IA

DIODE(AVG)

–

.

=×

=

08

12

5

12

047

.

For this system, a 1N5817 would be a good choice (rated at 20 V

and 1 A). Do not use catch diodes rated less than 1 A. Even though

the average current can be less than 1 A under normal operating

conditions, since the diode current will be much higher under fault

conditions. The worst case fault condition for the diode occurs when

the regulator becomes slightly overloaded (sometimes called a soft

Table III. Capacitor Selection Guide

Max

Package

Vendor/

Value

ESR

*

Voltage

Dimensions (mm)

Series

( F)

( )

(V)

Type

W

L

H

AVX

TPS

100

0.150

6.3

Tantalum

3.2

6.0

2.6

TPS

47

0.150

16

Tantalum

4.3

7.3

2.9

TPS

100

0.100

10

Tantalum

4.3

7.3

2.9

TPS

100

0.125

16

Tantalum

4.3

7.3

2.9

Y5V

10

~0.040

10

MLC

1.6

3.2

1.5

Y5V

10

~0.040

16

MLC

2.5

3.2

1.7

Y5V

18

~0.040

10

MLC

2.5

3.2

1.7

Y5V

22

~0.040

10

MLC

2.5

3.2

1.7

Sprague

593D

47

0.150

16

Tantalum

4.3

7.3

2.8

593D

68

0.150

16

Tantalum

4.3

7.3

2.8

593D

100

0.100

10

Tantalum

4.3

7.3

2.8

593D

100

0.100

16

Tantalum

4.3

7.3

4.0

Tokin

CU

10

~0.040

10

MLC

1.6

3.2

1.6

CU

10

~0.040

25

MLC

2.7

5.7

2.5

CU

18

~0.040

25

MLC

5.0

5.7

2.5

CU

10

~0.040

50

MLC

5.0

5.7

3.0

CU

22

~0.030

25

MLC

5.0

5.7

3.0

*Maximum ESR ratings at 100 kHz; MLC = multilayer ceramic.

Table IV. Capacitor Manufacturers

Company

Phone

Fax

Web Address

AVX

(803) 448-9411

(803) 448-1943

www.avxcorp.com

Kemet

(864) 963-6300

(864) 963-6521

www.kemet.com

Murata (USA)

(800) 831-9172

(770) 436-3030

www.murata.com

Nemco

(800) 227-4058

(650) 571-0825

www.nemcocaps.com

Sprague

(207) 324-4140

(207) 324-7223

www.vishay.com

Tokin (USA)

(408) 432-8020

(408) 434-0375

www.tokin.com

Tokin (Japan)

81-22-211-1281

81-22-211-0975

www.tokin.com

Taiyo Yuden (USA)

(800) 348-2496

(847) 925-0899

www.t-yuden.com

Taiyo Yuden (Japan)

81-33-833-5441

81-33-835-4754

www.t-yuden.com