lt3741 Linear Technology Corporation, lt3741 Datasheet - Page 13

• Manufacturer Part Number: lt3741
• Description: High Power, Constant Current, Constant Voltage, Step-down Controller
• Manufacturer: Linear Technology Corporation

applicaTions inFormaTion
Programming Inductor Current
The analog voltage at the CTRL1 pin is buffered and
produces a reference voltage, V
resistor. The regulated average inductor current is deter-
mined by:
where R
age inductor current, which is equal to the output current.
Figure 2 shows the maximum output current vs R
maximum power dissipation in the resistor will be:
Table 1 contains several resistors values, the corresponding
maximum current and power dissipation in the sense resis-
tor. Susumu, Panasonic and Vishay offer accurate sense
resistors. Figure 3 shows the power dissipation in R
Table 1. Sense Resistor Values
MAXIMUM OUTPUT
I
P
CURRENT (A)
O
Figure 2. R
RS
=
=
10
25
30 •
1
5
V
S
CTRL
(
is the external sense resistor and I
0 05
30
25
20
15
10
.
R
5
0
R
S
0
S
1
S
Value Selection for Regulated Output Current
V
2
)
RESISTOR, R
2
4
6
50
10
5
2
8
R
S
10
(m )
S
(mΩ)
12
CTRL
14
POWER DISSIPATION (W)
16
, across an internal
18
3741 F02
20
0.05
0.25
1.25
O
0.5
is the aver-
S
. The
S
.
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
SENSE
should be at least 20% higher than the maximum regu-
lated current. The following equation sizes the inductor
for best performance:
where V
current in the inductor and f
Using this equation, the inductor will have approximately
15% ripple at maximum regulated current.
Table 2. Recommended Inductor Manufacturers
L
=



–
Würth Electronics
O
0 3
pins. The saturation current for the inductor
V
is the output voltage, I
. •
NEC-Tokin
IN
VENDOR
Coilcraft
1.4
1.2
1.0
0.8
0.6
0.4
Sumida
0.2
Vishay
0
•
f I
0
Figure 3. Power Dissipation in R
S O
V
O
• •
2
–
4
V
O
V
2
6
IN



8
R
S
10
(m )
S
is the switching frequency.
O
12
is the maximum regulated
14
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16
WEBSITE
18 20
3741 F03
S
LT3741

+
and
3741f