Datasheet

LT3465/LT3465A
12
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APPLICATIO S I FOR ATIO
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Figure 9.
Open-Circuit Protection
The LT3465 and LT3465A have an internal open-circuit
protection circuit. In the cases of output open circuit,
when the LEDs are disconnected from the circuit or the
LEDs fail, the V
OUT
is clamped at 30V. The LT3465 and
LT3465A will then switch at a very low frequency to
minimize the input current. V
OUT
and input current during
output open circuit are shown in the Typical Performance
Characteristics.
Board Layout Consideration
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
To maximize efficiency, switch rise and fall times are
made as short as possible. To prevent electromagnetic
interference (EMI) problems, proper layout of the high
frequency switching path is essential. Place C
OUT
next to
the V
OUT
and GND pins. Always use a ground plane under
the switching regulator to minimize interplane coupling.
In addition, the ground connection for the feedback
resistor R1 should be tied directly to the GND pin and not
shared with any other component, ensuring a clean, noise-
free connection. Recommended component placement is
shown in Figure 8.
Start-Up Input Current (LT3465A)
As previously mentioned, the LT3465A does not have an
internal soft-start circuit. Inrush current can therefore rise
to approximately 400mA as shown in Figure 9 when
driving 4 LEDs. The LT3465 has an internal soft-start
circuit and is recommended if inrush current must be
minimized.
Figure 8. Recommended Component Placement.
1
C
OUT
L
R
FB
2
3
6
5
4
C
IN
GND
3465A F08a
V
IN
CTRL
FB
200mV/DIV
CTRL
2V/DIV
50µs/DIV
3465A F09
I
IN
200mV/DIV