LT3682 LINER [Linear Technology], LT3682 Datasheet - Page 15

• Manufacturer Part Number: LT3682
• Description: 1A Micropower Step-Down
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Table 2. Capacitor Vendors
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.
Diode Selection
The catch diode (D1 from block diagram) conducts current
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:
I
D AVG
(
)
=
I
OUT
•(
− 1
DC
PHONE
[phone]
[phone]
[phone]
[phone]
[phone]
)
URL
www.panasonic.com
www.kemet.com
www.sanyovideo.com
www.murata.com
www.avxcorp.com
www.taiyo-yuden.com
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
than the input voltage. If transients at the input of up to
60V are expected, use a diode with a reverse voltage rat-
ing only higher than the maximum OVLO of 41V. Table 3
lists several Schottky diodes and their manufacturers. If
operating at high ambient temperatures, consider using
a Schottky with low reverse leakage.
Audible Noise
Ceramic capacitors are small, robust and have very
low ESR. However, ceramic capacitors can sometimes
cause problems when used with the LT3682 due to their
piezoelectric nature. When in Burst Mode operation, the
LT3682’s switching frequency depends on the load current,
and at very light loads the LT3682 can excite the ceramic
capacitor at audio frequencies, generating audible noise.
Since the LT3682 operates at a lower current limit during
Burst Mode operation, the noise is typically very quiet. If
this is unacceptable, use a high performance tantalum or
electrolytic capacitor at the output.
I
D AVG MAX
(
)
PART SERIES
Ceramic,
Polymer,
Tantalum
Ceramic,
Tantalum
Ceramic,
Polymer,
Tantalum
Ceramic
Ceramic,
Tantalum
Ceramic
=
2
A
+
2
1
•
V
L
IN
•
150
COMMENTS
EEF Series
T494, T495
POSCAP
TPS Series
ns
IN
> OVLO (41V maxi-
LT3682
15
3682f