LTC3209-2 Linear Technology, LTC3209-2 Datasheet - Page 10

• Manufacturer Part Number: LTC3209-2
• Description: 600mA Main/Camera LED Controller
• Manufacturer: Linear Technology

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10
LTC3209-1/LTC3209-2
Consider the example of driving white LEDs from a 3.1V
supply. If the LED forward voltage is 3.8V and the current
sources require 100mV, the advantage voltage for 1.5x
mode is 3.1V • 1.5 – 3.8V – 0.1V or 750mV. Notice that if
the input voltage is raised to 3.2V, the advantage voltage
jumps to 900mV—a 20% improvement in available
strength.
From Figure 1, for 1.5x mode the available current is given
by:
For 2x mode, the available current is given by:
OPERATIO
I
I
OUT
OUT
=
=
Figure 2. Typical 1.5x R
1 5 .
2
3.2
3.0
2.8
2.6
2.4
2.2
2.0
V
–40
BAT
V
V
V
C2 = C3 = C4 = 2.2µF
BAT
R
BAT
CPO
R
OL
–
OL
U
= 3V
= 4.2V
–15
–
V
CPO
V
CPO
TEMPERATURE (°C)
10
35
OL
vs Temperature
60
3209 G06
85
Notice that the advantage voltage in this case is
3.1V • 2 – 3.8V – 0.1V = 2.3V. R
a significant overall increase in available current is achieved.
Typical values of R
shown in Figures 2 and 3.
Shutdown Current
Shutdown occurs when all the current source data bits
have been written to zero or when DV
UVLO threshold.
Although the LTC3209-1/LTC3209-2 is designed to have
very low shutdown current, it will draw about 3µA from
V
LTC3209-1/LTC3209-2 is in shutdown when DV
grounded. Note, however that all of the logic signals that
are referenced to DV
at DV
absolute maximum specifications on these pins.
BAT
when in shutdown. Internal logic ensures that the
CC
or below (i.e., ground) to avoid violation of the
3.8
3.6
3.4
3.2
3.0
2.8
2.6
Figure 3. Typical 2x R
–40
V
V
C2 = C3 = C4 = 2.2µF
BAT
CPO
= 3V
= 4.8V
–15
OL
CC
TEMPERATURE (°C)
(SCL, SDA, CAMHL) will need to be
as a function of temperature are
10
OL
35
OL
vs Temperature
is higher in 2x mode but
60
CC
is below the DV
3209 G08
85
320912fa
CC
CC
is