LT3498
APPLICATIONS INFORMATION — LED DRIVER
Table 2: Recommended Ceramic Capacitor Manufacturers
Inrush Current
Taiyo Yuden
AVX
Murata
(800) 368-2496
www.t-yuden.com
(803) 448-9411
www.avxcorp.com
(714) 852-2001
The LT3498 LED Driver has a built-in Schottky diode.
When supply voltage is applied to the V IN pin, an inrush
current ?ows through the inductor and Schottky diode
and charges up the CAP1 voltage. The Schottky diode
www.murata.com
Overvoltage Protection
The LED driver of the LT3498 has 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 open-circuit, V CAP1 is clamped at 27V (typ). The LED
driver will then switch at a very low frequency to minimize
for the LED Driver of the LT3498 can sustain a maximum
current of 1A.
For low DCR inductors, which are usually the case for this
application, the peak inrush current can be simpli?ed as
follows:
r
=
2 ?L
input current. The V CAP1 and input current during output
open-circuit are shown in the Typical Performance Char-
acteristics. Figure 3 shows the transient response when
=
1
L ?C
r 2
4 ? L 2
the LEDs are disconnected.
I PK =
V IN – 0.6
L?
? exp –
?
2
where L is the inductance, r is the DCR of the inductor
I L
200mA/DIV
and C is the output capacitance.
Table 3 gives inrush peak currents for some component
V CAP1
10V/DIV
LEDs DISCONNECTED
AT THIS POINT
selections.
Table 3: Inrush Peak Currents
500μs/DIV
V IN = 3.6V
FRONT PAGE APPLICATION CIRCUIT
3498 F03
V IN (V)
4.2
4.2
r ( Ω )
0.58
1.6
L (μH)
15
15
C OUT (μF)
1
1
I P (A)
0.828
0.682
Figure 3. Transient Response with
LEDs Disconnected From Output
4.2
4.2
0.8
0.739
15
15
1
1
0.794
0.803
3498fa
10
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