lt3480emse-trpbf Linear Technology Corporation, lt3480emse-trpbf Datasheet - Page 12

• Manufacturer Part Number: lt3480emse-trpbf
• Description: 38v, 2a, 2.4mhz Step-down Switching Regulator With 70?a Quiescent Current
• Manufacturer: Linear Technology Corporation

LT3480
APPLICATIONS INFORMATION
capacitor if the compensation network is also adjusted
to maintain the loop bandwidth. A lower value of output
capacitor can be used to save space and cost but transient
performance will suffer. See the Frequency Compensation
section to choose an appropriate compensation network.
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 0.05 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
Table 2. Capacitor Vendors
12
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
to the regulator input voltage. Use a Schottky diode with a
reverse voltage rating greater than the input voltage. The
overvoltage protection feature in the LT3480 will keep the
switch off when V
rated Schottky even when V
lists several Schottky diodes and their manufacturers.
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 LT3480 due to their piezoelectric nature.
When in Burst Mode operation, the LT3480’s switching
frequency depends on the load current, and at very light
loads the LT3480 can excite the ceramic capacitor at audio
frequencies, generating audible noise. Since the LT3480
operates at a lower current limit during Burst Mode
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
IN
> 38V which allows the use of 40V
(V)
V
20
40
20
30
20
30
40
30
30
R
IN
I
(A)
ranges up to 60V. Table 3
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
3480fb