LT1937 LINER [Linear Technology], LT1937 Datasheet - Page 10

• Manufacturer Part Number: LT1937
• Description: 20mA LED Driver and OLED Driver with Integrated Schottky in 3mm x 2mm DFN
• Manufacturer: LINER [Linear Technology]

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Taiyo Yuden
AVX
Murata
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
driver will then switch at a very low frequency to minimize
input current. The V
open-circuit are shown in the Typical Performance Char-
acteristics. Figure 3 shows the transient response when
the LEDs are disconnected.
LT3498
APPLICATIONS INFORMATION—LED DRIVER
10
200mA/DIV
10V/DIV
V
CAP1
I
L
Figure 3. Transient Response with
LEDs Disconnected From Output
V
FRONT PAGE APPLICATION CIRCUIT
IN
CAP1
= 3.6V
CAP1
is clamped at 27V (typ). The LED
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and input current during output
500 s/DIV
LEDs DISCONNECTED
AT THIS POINT
3498 F03
Inrush Current
The LT3498 LED Driver has a built-in Schottky diode.
When supply voltage is applied to the V
current fl ows 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.
For low DCR inductors, which are usually the case for this
application, the peak inrush current can be simplifi ed as
follows:
where L is the inductance, r is the DCR of the inductor
and C is the output capacitance.
Table 3 gives inrush peak currents for some component
selections.
Table 3: Inrush Peak Currents
I
V
PK
IN
4.2
4.2
4.2
4.2
(V)
2
V
r
•
L C
IN
L
L
1
•
•
– .
0 6
–
0.739
r (Ω)
0.58
1.6
0.8
4
r
• exp –
•
2
L
2
L (µH)
15
15
15
15
•
2 2
C
OUT
1
1
1
1
IN
(µF)
pin, an inrush
0.828
0.682
0.794
0.803
I
P
(A)
3498f