LTC3209-1 Datasheet, PDF (12/20 Pages) Linear Technology – 600mA Main/Camera LED Controller

LTC3209-1/LTC3209-2
OPERATIO
CAMHL
The CAMHL pin quickly selects the camera high register
for flash applications without reaccessing the I²C port.
When low the CAM current range will be controlled by the
camera low 4-bit register. When CAMHL is asserted high
the current range will be set by the camera high 4-bit
register. The dropout delay is reduced from 150ms to 2ms
when CAMHL is asserted high so that the charge pump
can quickly change modes if required. When CAMHL
is asserted from high to low the charge pump mode is reset
to 1x.
Thermal Protection
The LTC3209-1/LTC3209-2 have built-in overtemperature
protection. At internal die temperatures of around 150°C
thermal shutdown will occur. This will disable all of the
current sources and charge pump until the die has cooled
by about 15°C. This thermal cycling will continue until the
fault has been corrected.
R_REF Current Set Resistor
The current set resistor is connected between the R_REF pin
and ground. This resistor sets the full-scale current for all
three displays (MAIN, CAM and AUX) according to the
following equations:
MAIN = ^1.23V • 550
R_REF
CAM = ^1.23V • 7900
R_REF
CAM = ^1.23V • 3950
R_REF
AUX
=
1.23V
R_REF
•
272
(LTC3209-1)
(LTC3209-2)
A 24.3k, 1% resistor provides full-scale currents of 28mA
for the MAIN; 400mA (total) current for CAM and 13.75mA
for AUX current sources.
This input is protected against shorts to ground or
low value resistors <10k. When a fault is detected the
reference current amplifier is current limited. In addition
the current source outputs and charge pump are disabled.
Mode Switching
The LTC3209-1/LTC3209-2 will automatically switch from
1x mode to 1.5x mode and subsequently to 2x mode
whenever a dropout condition is detected at an LED pin.
Dropout occurs when a current source voltage becomes
too low for the programmed current to be supplied. When
switching modes the mode change will not occur unless
dropout has existed for 150ms. This delay will allow the
LEDs to warm up and achieve the final LED forward voltage
value. The dropout delay can be reduced to 2ms by
programming the Drop2ms bit C2 in the REGC register or
when the CAMHL pin is switched high when controlling
the CAM LEDs.
The mode will automatically switch back to 1x whenever a
data bit is updated via the I²C port or when CAMHL
switches from high to low. If the part is forced into either
1.5x mode or 2x mode to operate as a fixed voltage power
supply over I²C, no mode switching will occur until an I²C
update is given.
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