lt3685emse-trpbf Linear Technology Corporation, lt3685emse-trpbf Datasheet - Page 12

• Manufacturer Part Number: lt3685emse-trpbf
• Description: 38v, 2a, 2.4mhz Step-down Switching Regulator
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
LT3685
where f
output capacitance in μF. Use X5R or X7R types. This
choice will provide low output ripple and good transient
response. Transient performance can be improved with a
higher value 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 compen-
sation 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 volt-
age 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
12
Table 2. Capacitor Vendors
VENDOR
Panasonic
Kemet
Sanyo
Murata
AVX
Taiyo Yuden
SW
is in MHz, and C
PHONE
[phone]
[phone]
[phone]
[phone]
[phone]
OUT
is the recommended
URL
www.panasonic.com
www.kemet.com
www.sanyovideo.com
www.murata.com
www.avxcorp.com
www.taiyo-yuden.com
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 Schottky diode with a
reverse voltage rating greater than the input voltage. The
overvoltage protection feature in the LT3685 will keep the
switch off when V
rated Schottky even when V
lists several Schottky diodes and their manufacturers.
Table 3. Diode Vendors
PART NUMBER
On Semicnductor
MBRM120E
MBRM140
Diodes Inc.
B260
PDS360
B220
B230
DFLS240L
International Rectifi er
10BQ030
20BQ030
I
D(AVG)
OUT
PART SERIES
Ceramic,
Polymer,
Tantalum
Ceramic,
Tantalum
Ceramic,
Polymer,
Tantalum
Ceramic
Ceramic,
Tantalum
Ceramic
= I
is the output load current. The only reason to
OUT
(V
IN
IN
> 45V which allows the use of 45V
(V)
– V
V
20
40
60
60
20
30
40
30
30
R
OUT
IN
)/V
I
(A)
ranges up to 60V. Table 3
AVE
1
1
2
3
2
2
2
1
2
IN
COMMANDS
EEF Series
T494, T495
POSCAP
TPS Series
V
F
(mV)
530
550
420
AT 1A
V
F
(mV)
595
700
510
500
500
500
470
470
AT 2A
3685f