Datasheet

LT1913
13
1913f
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 speci-
fi 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:
I
D(AVG)
= I
OUT
(V
IN
– V
OUT
)/V
IN
where I
OUT
is the output load current. The only reason to
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. Table
3 lists several Schottky diodes and their manufacturers.
Table 3. Diode Vendors
PART NUMBER
V
R
(V)
I
AVE
(A)
V
F
AT 3A
(mV)
On Semiconductor
MBRA340 40 3 500
Diodes Inc.
B330
B320
30
20
3
3
500
450
Frequency Compensation
The LT1913 uses current mode control to regulate the
output. This simplifi es loop compensation. In particular, the
LT1913 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
VENDOR PHONE URL PART SERIES COMMANDS
Panasonic [phone] www.panasonic.com Ceramic,
Polymer,
Tantalum
EEF Series
Kemet [phone] www.kemet.com Ceramic,
Tantalum T494, T495
Sanyo [phone] www.sanyovideo.com Ceramic,
Polymer,
Tantalum
POSCAP
Murata [phone] www.murata.com Ceramic
AVX www.avxcorp.com Ceramic,
Tantalum TPS Series
Taiyo Yuden [phone] www.taiyo-yuden.com Ceramic
Table 2. Capacitor Vendors
APPLICATIONS INFORMATION