LT3479EDE データシートの表示（PDF） - Linear Technology
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LT3479EDE
Linear Technology
LT3479EDE Datasheet PDF : 20 Pages
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LT3479
APPLICATIONS INFORMATION
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 ex-
ternal inductor senses the inductor current at all times.
When it exceeds 5A, a soft-start cycle is initiated. Figure 9
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
illustrates 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 VS pin open to disable this feature.
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0.1
10
RT (kΩ)
100
3479 F07
Figure 7. Switching Frequency
90
1MHz
85
80
2MHz
75
70
65
60
55
50
0
0.2
0.4
0.6
0.8
IOUT (A)
3479 F08
Figure 8. Efficiency vs Switching Frequency
VSW
10V/DIV
IL
4V/DIV
VSS
2V/DIV
VOUT
20V/DIV
20μs/DIV
3479 F09
Figure 9. Output Overload with
Inrush Current Protection Enabled
VSW
10V/DIV
IL
4V/DIV
VSS
2V/DIV
VOUT
20V/DIV
20μs/DIV
3479 F10
Figure 10. Output Overload with
Inrush Current Protection Disabled
VIN
VOUT
LT3479
BOOST
REGULATOR
0.5Ω
3479 F11
Figure 11. Circuit for Output Overload
3479fc
11
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