
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
μ
F to 220
μ
F 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:
I
I
V
V
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:
I
A
DIODE(AVG)
–
.
=
×
=
0 8
.
12
5
12
0 47
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
Voltage
(V)
Package
Dimensions (mm)
W
Vendor/
Series
Value
( F)
ESR
*
( )
Type
L
H
AVX
TPS
TPS
TPS
TPS
Y5V
Y5V
Y5V
Y5V
100
47
100
100
10
10
18
22
0.150
0.150
0.100
0.125
~0.040
~0.040
~0.040
~0.040
6.3
16
10
16
10
16
10
10
Tantalum
Tantalum
Tantalum
Tantalum
MLC
MLC
MLC
MLC
3.2
4.3
4.3
4.3
1.6
2.5
2.5
2.5
6.0
7.3
7.3
7.3
3.2
3.2
3.2
3.2
2.6
2.9
2.9
2.9
1.5
1.7
1.7
1.7
Sprague
593D
593D
593D
593D
47
68
100
100
0.150
0.150
0.100
0.100
16
16
10
16
Tantalum
Tantalum
Tantalum
Tantalum
4.3
4.3
4.3
4.3
7.3
7.3
7.3
7.3
2.8
2.8
2.8
4.0
Tokin
CU
CU
CU
CU
CU
10
10
18
10
22
~0.040
~0.040
~0.040
~0.040
~0.030
10
25
25
50
25
MLC
MLC
MLC
MLC
MLC
1.6
2.7
5.0
5.0
5.0
3.2
5.7
5.7
5.7
5.7
1.6
2.5
2.5
3.0
3.0
*
Maximum ESR ratings at 100 kHz; MLC = multilayer ceramic.
Table IV. Capacitor Manufacturers
Company
Phone
Fax
Web Address
AVX
Kemet
Murata (USA)
Nemco
Sprague
Tokin (USA)
Tokin (Japan)
Taiyo Yuden (USA)
Taiyo Yuden (Japan)
(803) 448-9411
(864) 963-6300
(800) 831-9172
(800) 227-4058
(207) 324-4140
(408) 432-8020
81-22-211-1281
(800) 348-2496
81-33-833-5441
(803) 448-1943
(864) 963-6521
(770) 436-3030
(650) 571-0825
(207) 324-7223
(408) 434-0375
81-22-211-0975
(847) 925-0899
81-33-835-4754
www.avxcorp.com
www.kemet.com
www.murata.com
www.nemcocaps.com
www.vishay.com
www.tokin.com
www.tokin.com
www.t-yuden.com
www.t-yuden.com