Datasheet

LTC3215
8
3215fc
OPERATION
Mode Switching
The LTC3215 will automatically switch from 1x mode to
1.5x mode, and subsequently from 1.5x mode to 2x mode
whenever a dropout condition is detected at the I
LED
pin.
The part will wait approximately 2ms before switching
to the next mode. This delay allows the LED to warm up
and reduce its forward voltage which may remove the
dropout condition.
In order to reset
the part back into 1x mode, the LTC3215
must be brought into shutdown (EN = LOW). Immediately
after the part has been brought to shutdown, it may be
enabled into the 1x mode via the EN pin. An internal com-
parator will not allow the main switches to connect V
IN
and CPO in 1x mode until the voltage at the CPO pin has
decayed to less than
or equal to the voltage at the V
IN
pin.
Figure 2
(2a) (2b)
2.2µF 2.2µF
4.7µF
I
LED
*
I
LED
V
IN
2.9V TO 4.4V
2.2µF
ON/OFF
TORCH/FLASH
EN
LTC3215
R2
*I
TORCH
= [(1.22V/R1) – ((V
IO
– 1.22V)/R2)] • 3270
I
FLASH
= [(1.22V/(R1 • R2/(R1 + R2))] • 3270
C1
+
C1
–
C2
+
C2
–
I
SET
3215 F02a
CPO
R1
V
IO
V
IO
µP
2.2µF 2.2µF
4.7µF
1µF
I
LED
V
IN
2.9V TO 4.4V
2.2µF
EN
LTC3215
C1
+
C1
–
C2
+
C2
–
I
SET
3215 F02b
CPO
1k
9.31k
1%
9.31k
1%
PWM