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LT3741 Datasheet(PDF) 13 Page - Linear Technology

Part # LT3741
Description  High Power, Constant Current, Constant Voltage, Step-Down Controller
PDF  24 Pages
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Manufacturer  LINER [Linear Technology]
Direct Link  http://www.linear.com
Logo LINER - Linear Technology

LT3741 Datasheet(HTML) 13 Page - Linear Technology

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LT3741

3741f
applicaTions inFormaTion
Programming Inductor Current
The analog voltage at the CTRL1 pin is buffered and
produces a reference voltage, VCTRL, across an internal
resistor. The regulated average inductor current is deter-
mined by:
I
V
R
O
CTRL
S
=
1
30 •
where RS is the external sense resistor and IO is the aver-
age inductor current, which is equal to the output current.
Figure 2 shows the maximum output current vs RS. The
maximum power dissipation in the resistor will be:
P
V
R
RS
S
= (
)
0 05 2
.
Table1containsseveralresistorsvalues,thecorresponding
maximumcurrentandpowerdissipationinthesenseresis-
tor. Susumu, Panasonic and Vishay offer accurate sense
resistors. Figure 3 shows the power dissipation in RS.
Table 1. Sense Resistor Values
MAXIMUM OUTPUT
CURRENT (A)
RESISTOR, RS (mΩ) POWER DISSIPATION (W)
1
50
0.05
5
10
0.25
10
5
0.5
25
2
1.25
Inductor Selection
Size the inductor to have no less than 30% peak-to-peak
ripple. The overcurrent set point is equal to the high
level regulated current level set by the CTRL1 pin with
an additional 23mV offset between the SENSE+ and
SENSE– pins. The saturation current for the inductor
should be at least 20% higher than the maximum regu-
lated current. The following equation sizes the inductor
for best performance:
L
V
V
V
f I V
IN
O
O
S O
IN
=
•
–
. • • •
2
0 3
whereVOistheoutputvoltage,IOisthemaximumregulated
current in the inductor and fS is the switching frequency.
Using this equation, the inductor will have approximately
15% ripple at maximum regulated current.
Table 2. Recommended Inductor Manufacturers
VENDOR
WEBSITE
Coilcraft
www.coilcraft.com
Sumida
www.sumida.com
Vishay
www.vishay.com
Würth Electronics
www.we-online.com
NEC-Tokin
www.nec-tokin.com
RS (m)
0
0
0.2
0.6
0.8
1.0
1.4
2
10
14
3741 F03
0.4
1.2
8
18 20
4
6
12
16
RS (m)
0
10
20
30
5
15
25
4
8
12
16
3741 F02
20
2
0
6
10
14
18
Figure 2. RS Value Selection for Regulated Output Current
Figure 3. Power Dissipation in RS



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