LT3481 LINER [Linear Technology], LT3481 Datasheet - Page 12

• Manufacturer Part Number: LT3481
• Description: 36V, 2A, 2.8MHz Step-Down Switching Regulator with 50?A Quiescent Current
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
LT3481
When choosing a capacitor, look carefully through the
data sheet to fi nd out what the actual capacitance is under
operating conditions (applied voltage and temperature).
A physically larger capacitor, or one with a higher voltage
rating, may be required. High performance tantalum or
electrolytic capacitors can be used for the output capacitor.
Low ESR is important, so choose one that is intended for
use in switching regulators. The ESR should be specifi ed
by the supplier, and should be 0.05Ω or less. Such a
capacitor will be larger than a ceramic capacitor and will
have a larger capacitance, because the capacitor must be
large to achieve low ESR. Table 2 lists several capacitor
vendors.
Catch Diode
The catch diode conducts current only during switch off
time. Average forward current in normal operation can
be calculated from:
where I
consider a diode with a larger current rating than necessary
for nominal operation is for the worst-case condition of
shorted output. The diode current will then increase to the
typical peak switch current. Peak reverse voltage is equal
to the regulator input voltage. Use a diode with a reverse
voltage rating greater than the input voltage. Table 3 lists
several Schottky diodes and their manufacturers.
12
Table 2. Capacitor Vendors
VENDOR
Panasonic
Kemet
Sanyo
Murata
AVX
Taiyo Yuden
I
D(AVG)
OUT
= I
is the output load current. The only reason to
OUT
PHONE
[phone]
[phone]
[phone]
[phone]
[phone]
(V
IN
– V
OUT
)/V
IN
URL
www.panasonic.com
www.kemet.com
www.sanyovideo.com
www.murata.com
www.avxcorp.com
www.taiyo-yuden.com
Table 3. Diode Vendors
Ceramic Capacitors
Ceramic capacitors are small, robust and have very low
ESR. However, ceramic capacitors can cause problems
when used with the LT3481 due to their piezoelectric nature.
When in Burst Mode operation, the LT3481’s switching
frequency depends on the load current, and at very light
loads the LT3481 can excite the ceramic capacitor at audio
frequencies, generating audible noise. Since the LT3481
operates at a lower current limit during Burst Mode op-
eration, the noise is typically very quiet to a casual ear.
If this is unacceptable, use a high performance tantalum
or electrolytic capacitor at the output.
PART NUMBER
On Semicnductor
MBRM120E
MBRM140
Diodes Inc.
B120
B130
B220
B230
DFLS240L
International Rectifi er
10BQ030
20BQ030
PART SERIES
Ceramic,
Polymer,
Tantalum
Ceramic,
Tantalum
Ceramic,
Polymer,
Tantalum
Ceramic
Ceramic,
Tantalum
Ceramic
(V)
V
20
40
20
30
20
30
40
30
30
R
I
(A)
AVE
1
1
1
1
2
2
2
1
2
COMMANDS
EEF Series
T494, T495
POSCAP
TPS Series
V
F
(mV)
530
550
500
500
420
AT 1A
V
F
(mV)
595
500
500
500
470
470
AT 2A
3481fb