Datasheet
4
LTC3490
3490fa
UU
U
PI FU CTIO S
CELLS (Pin 1): A logic input to set the low-battery and
undervoltage shutdown thresholds. A logic low (tied to
GND) will set the thresholds for 1 cell. A logic high (tied to
V
IN
) will set the thresholds for 2 cells.
V
IN
(Pin 2): Supply Voltage.
SW (Pin 3): Switch Input. Connect this pin to an external
inductor from V
IN
.
GND (Pin 4): Circuit Ground.
LED (Pin 5): Output Drive Current to LED.
CAP (Pin 6): Filter Capacitor. A 4.7µF low ESR capacitor
should be tied to this pin.
LOBAT (Pin 7): Low active, open-drain logic output indi-
cating a low-battery condition.
CTRL/SHDN (Pin 8): Analog Control Voltage and Shut-
down. When V
IN
• 0.2 < V
CTRL
< V
IN
• 0.9, the LED drive
current varies according to the formula:
I
V
V
mA
LED
CTRL
IN
=
⎛
⎝
⎜
⎞
⎠
⎟
500 0 2•–.
When V
CTRL
> V
IN
• 0.9, the LED drive current is clamped
at 350mA. When V
CTRL
< V
IN
• 0.2, then the part is in low
power shutdown.
Exposed Pad (Pin 9, DD Package): Ground. This pin must
be soldered to the PCB to provide both electrical contact
to ground and good thermal contact to the PCB.
I
LED
vs V
LED
V
LED
(V)
2.8
340
I
LED
(mA)
342
346
348
350
360
354
3 3.2
3.4 3.6 3.8
3490 G04
344
356
358
352
4
V
IN
= 2.4V
TYPICAL PERFOR A CE CHARACTERISTICS
UW
I
LED
(mA)
0
0
EFFICIENCY (%)
10
30
40
50
100
70
100
200
3490 G05
20
80
90
60
300
400
V
IN
= 2.4V
V
IN
= 1.2V
Efficiency vs I
LED