LT3498
APPLICATIONS INFORMATION—LED DRIVER
Inrush Current
Table 2: Recommended Ceramic Capacitor Manufacturers
Taiyo Yuden
(800) 368-2496
The LT3498 LED Driver has a built-in Schottky diode.
www.t-yuden.com
When supply voltage is applied to the V pin, an inrush
IN
AVX
(803) 448-9411
www.avxcorp.com
current flows through the inductor and Schottky diode
and charges up the CAP1 voltage. The Schottky diode
for the LED Driver of the LT3498 can sustain a maximum
current of 1A.
Murata
(714) 852-2001
www.murata.com
Overvoltage Protection
For low DCR inductors, which are usually the case for this
application, the peak inrush current can be simplified as
follows:
The LED driver of the LT3498 has an internal open-circuit
protectioncircuit.Inthecasesofoutputopencircuit,when
the LEDs are disconnected from the circuit or the LEDs
fail open-circuit, V
driver will then switch at a very low frequency to minimize
input current. The V and input current during output
open-circuit are shown in the Typical Performance Char-
acteristics. Figure 3 shows the transient response when
the LEDs are disconnected.
r
α =
is clamped at 27V (typ). The LED
CAP1
2•L
r2
4•L2
CAP1
1
L •C
ω =
–
V – 0.6
L •ω
α π
• exp – •
⎛
⎝
⎞
IN
IPK
=
⎜
⎟
⎠
ω 2
where L is the inductance, r is the DCR of the inductor
and C is the output capacitance.
I
L
200mA/DIV
Table 3 gives inrush peak currents for some component
selections.
Table 3: Inrush Peak Currents
V
CAP1
LEDs DISCONNECTED
AT THIS POINT
10V/DIV
3498 F03
V
(V)
r (Ω)
L (µH)
C
(µF)
I (A)
P
IN
OUT
500µs/DIV
V
= 3.6V
IN
4.2
0.58
1.6
15
15
15
15
1
0.828
0.682
0.794
0.803
FRONT PAGE APPLICATION CIRCUIT
4.2
4.2
4.2
1
1
1
Figure 3. Transient Response with
LEDs Disconnected From Output
0.8
0.739
3498f
10
Linear [ Linear ]
