Datasheet

LT3971A/LT3971A-5
15
3971af
APPLICATIONS INFORMATION
When choosing a capacitor, look carefully through the
data sheet to find 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. Table 3 lists several capacitor vendors.
Table 3. Recommended Ceramic Capacitor Vendors
MANUFACTURER WEBSITE
AVX www.avxcorp.com
Murata www.murata.com
Taiyo Yuden www.t-yuden.com
Vishay Siliconix www.vishay.com
TDK www.tdk.com
Catch 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:
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 diode with a reverse
voltage rating greater than the input voltage.
Table 4. Schottky Diodes. The Reverse Current Values Listed Are
Estimates Based Off of Typical Curves for Reverse Current
vs Reverse Voltage at 25°C.
PART NUMBER
V
R
(V)
I
AVE
(A)
V
F
at 1A
(mV)
V
F
at 2A
(mV)
I
R
at V
R
=
20V 25°C
(µA)
On Semiconductor
MBR0520L 20 0.5 30
MBR0540 40 0.5 620 0.4
MBRM120E 20 1 530 595 0.5
MBRM140 40 1 550 20
Diodes Inc.
B0530W 30 0.5 15
B0540W 40 0.5 620 1
B120 20 1 500 1.1
B130 30 1 500 1.1
B140 40 1 500 1.1
B150 50 1 700 0.4
B220 20 2 500 20
B230 30 2 500 0.6
B140HB 40 1 1
DFLS240L 40 2 500 4
DFLS140 40 1.1 510 1
DFLS160 60 1 500 2.5
DFLS2100 100 2 770 860 0.01
B240 40 2 500 0.45
Central Semiconductor
CMSH1 - 40M 40 1 500
CMSH1 - 60M 60 1 700
CMSH1 - 40ML 40 1 400
CMSH2 - 40M 40 2 550
CMSH2 - 60M 60 2 700
CMSH2 - 40L 40 2 400
CMSH2 - 40 40 2 500
CMSH2 - 60M 60 2 700