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DESCRIPTIO
350mA Constant Current Output
2.8V to 4V Output Compliance
1- or 2-Cell NiMH or Alkaline Input
Synchronous Rectification: Up to 90% Efficiency
Fixed Frequency Operation: 1.3MHz
Low Quiescient Current: <1mA
Very Low Shutdown Current: <50碌A
Open LED Output Limited to 4.7V
V
IN
Range: 1V to 3.2V
Dimming Control
Undervoltage Lockout to Protect Batteries
Low Profile (0.75mm) 3mm
脳
3mm Thermally
Enhanced 8-Lead DD and S8 Packages
The LTC
廬
3490 provides a constant current drive for 1W
LED applications. It is a high efficiency boost converter
that operates from 1 or 2 NiMH or alkaline cells and
generates 350mA of constant current with up to 4V of
compliance. It contains a 100m鈩?NFET switch and a
130m鈩?PFET synchronous rectifier. The fixed switching
frequency is internally set to 1.3MHz.
The LTC3490 limits the output voltage to 4.7V if the output
load is disconnected. It also features an analog dimming
capability that reduces the drive current proportional to
the CTRL/SHDN pin voltage. A low-battery logic output
signals when the battery has dropped below 1V/cell. An
undervoltage lockout circuit shuts down the LTC3490
when the battery voltage drops below 0.85V/cell. The
feedback loop is internally compensated to minimize com-
ponent count.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
APPLICATIO S
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Portable Lighting
Rechargeable Flashlights
TYPICAL APPLICATIO
3.3碌H
Single Cell Minimum Component LED Driver
100
90
80
V
IN
ON/OFF
1 NiMH OR
ALKALINE
CELL
SW
CAP
LTC3490
CTRL/SHDN LED
CELLS
1M
GND
LOBAT
350mA
4.7碌F
HIGH
CURRENT
LED
Efficiency vs V
IN
at V
LED
= 3.5V
I
OUT
= 350mA
70
EFFICIENCY (%)
60
50
40
30
20
10
+
3490 TA01
0
1
1.5
2
V
IN
(V)
2.5
3
3490 TA02
U
3490f
U
U
1
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