LT1933HS6 View Datasheet(PDF) - Linear Technology
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Description
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LT1933HS6 Datasheet PDF : 20 Pages
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LT1933
APPLICATIONS INFORMATION
saturation current should be about 30% higher. For robust
operation in fault conditions the saturation current should
be ~1A. To keep efficiency high, the series resistance (DCR)
should be less than 0.2Ω. Table 1 lists several vendors
and types that are suitable.
Of course, such a simple design guide will not always re-
sult in the optimum inductor for your application. A larger
value provides a slightly higher maximum load current,
and will reduce the output voltage ripple. If your load is
lower than 500mA, then you can decrease the value of
the inductor and operate with higher ripple current. This
allows you to use a physically smaller inductor, or one
with a lower DCR resulting in higher efficiency. There are
several graphs in the Typical Performance Characteristics
section of this data sheet that show the maximum load
current as a function of input voltage and inductor value
for several popular output voltages. Low inductance may
result in discontinuous mode operation, which is OK, but
further reduces maximum load current. For details of
maximum output current and discontinuous mode opera-
tion, see Linear Technology Application Note 44. Finally,
for duty cycles greater than 50% (VOUT/VIN > 0.5), there
is a minimum inductance required to avoid subharmonic
oscillations. Choosing L greater than 3(VOUT + VD) μH
prevents subharmonic oscillations at all duty cycles.
Catch Diode
A 0.5A or 1A Schottky diode is recommended for the catch
diode, D1. The diode must have a reverse voltage rating
equal to or greater than the maximum input voltage. The
ON Semiconductor MBR0540 is a good choice; it is rated
for 0.5A forward current and a maximum reverse voltage
of 40V. The MBRM140 provides better efficiency, and will
handle extended overload conditions.
Input Capacitor
Bypass the input of the LT1933 circuit with a 2.2μF or
higher value ceramic capacitor of X7R or X5R type. Y5V
types have poor performance over temperature and ap-
plied voltage, and should not be used. A 2.2μF ceramic
is adequate to bypass the LT1933 and will easily handle
the ripple current. However, if the input power source has
high impedance, or there is significant inductance due to
long wires or cables, additional bulk capacitance may be
necessary. This can be provided with a low performance
electrolytic capacitor.
Step-down regulators draw current from the input sup-
ply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage
ripple at the LT1933 and to force this very high frequency
Table 1.Inductor Vendors
Vendor
URL
Coilcraft
www.coilcraft.com
Sumida
www.sumida.com
Toko
Würth Elektronik
www.toko.com
www.we-online.com
Part Series
D01608C
MSS5131
MSS6122
CR43
CDRH4D28
CDRH5D28
D52LC
D53LC
WE-TPC MH
WE-PD4 S
WE-PD2 S
Inductance Range (μH)
10 to 22
10 to 22
10 to 33
10 to 22
10 to 33
22 to 47
10 to 22
22 to 47
10 to 22
10 to 22
10 to 47
Size (mm)
2.9 × 4.5 × 6.6
3.1 × 5.1 × 5.1
2.2 × 6.1 × 6.1
3.5 × 4.3 × 4.8
3.0 × 5.0 × 5.0
3.0 × 5.7 × 5.7
2.0 × 5.0 × 5.0
3.0 × 5.0 × 5.0
2.8 × 4.8 × 4.8
2.9 × 4.5 × 6.6
3.2 × 4.0 × 4.5
1933fe
8
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