lt3479efe-trpbf Linear Technology Corporation, lt3479efe-trpbf Datasheet - Page 9

• Manufacturer Part Number: lt3479efe-trpbf
• Description: 3a, Full Featured Dc/dc Converter With Soft-start And Inrush Current Protection
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
Increasing switching frequency reduces output voltage
ripple but also reduces efficiency. The user should set the
frequency for the maximum tolerable output voltage
ripple. Figure 8 shows a reduction in efficiency of about
4% between 1MHz and 2MHz operation in a typical
application.
Inrush Current Protection
The LT3479 features a novel inductor current sensing
circuit that protects the LT3479 during hot plugging and
short circuits. An internal resistor in series with the
external inductor senses the inductor current at all times.
When it exceeds 5A, a soft-start cycle is initiated. Figure 9
Figure 8. Efficiency vs Switching Frequency
3.5
3.0
2.5
2.0
1.5
1.0
0.5
90
85
70
65
60
55
50
80
75
0
0.1
0
Figure 7. Switching Frequency
U
0.2
U
I
R
OUT
T
0.4
10
(kΩ)
(A)
1MHz
2MHz
0.6
W
3479 F08
3479 F07
0.8
100
U
shows an output overload with inrush current protection
disabled. Notice that soft-start remains high, and that the
inductor current does not return to zero. Figure 10 illus-
trates the benefits of inrush current protection. The output
short initiates a new soft start cycle reducing the inductor
current. After the fault has passed, the inductor current
slowly returns to its equilibrium value. To ensure bond
wire integrity, the inductor current should not exceed 8A
for more than 10ms.
Bypassing the 8.5mΩ inductor current sense resistor
disables inrush current protection. Connect the inductor
supply trace and bypass capacitor to the L pin and leave
the V
V
V
V
V
OUT
OUT
SW
SW
V
V
SS
SS
I
I
L
L
S
10V/DIV
20V/DIV
10V/DIV
20V/DIV
4V/DIV
2V/DIV
4V/DIV
2V/DIV
pin open to disable this feature.
Figure 11. Circuit for Output Overload
Figure 10. Output Overload with
Inrush Current Protection Disabled
Figure 9. Output Overload with
Inrush Current Protection Enabled
V
REGULATOR
IN
LT3479
BOOST
V
OUT
20µs/DIV
20µs/DIV
0.5Ω
3479 F11
3479 F09
3479 F10
LT3479
3479fa
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