lt3695 Linear Technology Corporation, lt3695 Datasheet - Page 16

• Manufacturer Part Number: lt3695
• Description: 1a Fault Tolerant Micropower Step-down Regulator
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
LT3695
Table 3. Capacitor Vendors
VENDOR
Panasonic
Kemet
Sanyo
Murata
AVX
Taiyo Yuden
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 3 lists several capacitor
vendors.
Diode Selection
The catch diode (D1 from Block Diagram) conducts cur-
rent only during switch off time. Average forward current
in normal operation can be calculated from:
where DC is the duty cycle. The only reason to consider a
diode with larger current rating than necessary for nominal
operation is for the case of shorted or overloaded output
conditions. For the worst case of shorted output the diode
average current will then increase to a value that depends
on the following internal parameters: switch current limit,
catch diode (DA pin) current threshold and minimum
on-time. The worst case (taking maximum values for the
above mentioned parameters) is given by the following
expression:
Peak reverse voltage is equal to the regulator input voltage
if it is below the overvoltage protection threshold. This
feature keeps the switch off for V
mum). For inputs up to the maximum operating voltage
of 36V, use a diode with a reverse voltage rating greater
16
I
I
D(AVG)
D AVG MAX
(
)
= I
OUT
=
2
• (1 – DC)
A
+
2
1
•
PHONE
[phone]
[phone]
[phone]
[phone]
[phone]
V
L
IN
•
150
IN
ns
> V
OVLO
(39.9V maxi-
URL
www.panasonic.com
www.kemet.com
www.sanyovideo.com
www.murata.com
www.avxcorp.com
www.taiyo-yuden.com
Table 4. Schottky Diodes
PART NUMBER
On-Semiconducor
MBR0520L
MBR0540
MBRM120E
MBRM140
Diodes Inc.
B0530W
B0540W
B120
B130
B140
B220
B230
B140HB
DFLS240L
DFLS140
B240
Central Semiconductor
CMSH1-40M
CMSH1-40ML
CMSH2-40M
CMSH2-40L
CMSH2-40
than the input voltage. If transients at the input of up to
60V are expected, use a diode with a reverse voltage rat-
ing of 40V. Table 4 lists several Schottky diodes and their
manufacturers. If operating at high ambient temperatures,
consider using a Schottky with low reverse leakage.
PART SERIES
Ceramic, Polymer, Tantalum
Ceramic, Tantalum
Ceramic, Polymer, Tantalum
Ceramic
Ceramic, Tantalum
Ceramic
V
R
20
40
20
40
30
40
20
30
40
20
30
40
40
40
40
40
40
40
40
40
(V)
I
AVE
0.5
0.5
0.5
0.5
1.1
1
1
1
1
1
2
2
1
2
2
1
1
2
2
2
(A)
V
F
at 1A (mV)
COMMANDS
EEF Series
T494, T495
POSCAP
TPS Series
620
530
550
620
500
500
500
530
510
500
400
V
F
at 2A (mV)
595
500
500
500
500
550
400
500
3695f