lt3684emse-trpbf Linear Technology Corporation, lt3684emse-trpbf Datasheet - Page 13

• Manufacturer Part Number: lt3684emse-trpbf
• Description: 36v, 2a, 2.8mhz Step-down Switching Regulator
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
VENDOR
Panasonic
Kemet
Sanyo
Murata
AVX
Taiyo Yuden
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.
Table 2. Capacitor Vendors
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
PART NUMBER
On Semicnductor
MBRM120E
MBRM140
Diodes Inc.
B120
B130
B220
B230
DFLS240L
International Rectifi er
10BQ030
20BQ030
Frequency Compensation
The LT3684 uses current mode control to regulate the
output. This simplifi es loop compensation. In particular, the
LT3684 does not require the ESR of the output capacitor
for stability, so you are free to use ceramic capacitors to
achieve low output ripple and small circuit size. Frequency
compensation is provided by the components tied to the
V
and a resistor (R
tion, there may be lower value capacitor in parallel. This
capacitor (C
is used to fi lter noise at the switching frequency, and is
required only if a phase-lead capacitor is used or if the
output capacitor has high ESR.
C
pin, as shown in Figure 2. Generally a capacitor (C
PART SERIES
Ceramic,
Polymer,
Tantalum
Ceramic,
Tantalum
Ceramic,
Polymer,
Tantalum
Ceramic
Ceramic,
Tantalum
Ceramic
F
) is not part of the loop compensation but
C
) in series to ground are used. In addi-
(V)
V
20
40
20
30
20
30
40
30
30
R
I
(A)
AVE
EEF Series
T494, T495
POSCAP
TPS Series
1
1
1
1
2
2
2
1
2
COMMANDS
V
F
(mV)
530
550
500
500
420
AT 1A
LT3684
V
13
F
(mV)
595
500
500
500
470
470
AT 2A
3684f
C
)