LTC3208 Datasheet, PDF (11/24 Pages) Linear Technology – High Current Software Confi gurable Multidisplay LED Controller

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OPERATIO
LTC3208
Shutdown Current
Shutdown occurs when all the current source data bits
have been written to zero or when DV_CC is below the DV_CC
UVLO threshold.
Although the LTC3208 is designed to have very low shut-
down current, it will draw about 3µA from V_BAT when in
shutdown. Internal logic ensures that the LTC3208 is in
shutdown when DV_CC is grounded. Note, however, that
all of the logic signals that are referenced to DV_CC (SCL,
SDA, ENRGBS, CAMHL) will need to be at DV_CC or below
(i.e., ground) to avoid violation of the absolute maximum
specifications on these pins.
Serial Port
The microcontroller compatible I²C serial port provides all
of the command and control inputs for the LTC3208. Data
on the SDA input is loaded on the rising edge of SCL. D7
is loaded first and D0 last. There are seven data registers,
one address register and one sub-address register. Once
all address bits have been clocked into the address reg-
ister acknowledgment occurs. The sub-address register
is then written followed by writing the data register. Each
data register has a sub-address. After the data register
has been written a load pulse is created after the stop bit.
The load pulse transfers all of the data held in the data
registers to the DAC registers. The stop bit can be delayed
until all of the data master registers have been written.
At this point the LED current will be changed to the new
settings. The serial port uses static logic registers so there
is no minimum speed at which it can be operated.
MAIN and SUB Current Sources
There are four MAIN current sources and two SUB current
sources. Each bank of current sources has an 8-bit linear
DAC for current control. The output current range is 0 to
27.5mA in 256 steps.
The current sources are disabled when a block receives
an all zero data word. The supply current for that block is
reduced to zero. In addition each individual LED output
can be connected to CPO to turn off that particular current
source output and reduce operating current of the disabled
output to typically 10µA.
Camera Current Sources
There are four CAM current sources. This bank of current
sources has a 4-bit linear DAC for current control. The
output current range is 0 to 102mA in 16 steps.
The current sources are disabled when the block receives
an all zero data word. The supply current for the block is
reduced to zero. In addition each individual LED output
can be connected to CPO to turn off that particular current
source output and reduce operating current of the disabled
output to typically 10µA.
RGB Illuminators
The RED, GREEN and BLUE LEDs can be individually set
from 0µA to 27mA in 16 steps via three 4-bit exponential
DACs.
The current sources are individually disabled when an
all-zero data word is received. The supply current for the
current source is reduced to zero. These outputs can also
be used as open drain logic control outputs. For this reason
they will not be disabled when connected to CPO.
Auxiliary Current Sources
There are four AUX current sources. This bank of current
sources has a 4-bit linear DAC for current control. The
output current range is 0mA to 26mA in 16 steps.
In addition, each current source can be independently
connected to the CAM, SUB or MAIN DAC outputs. The
selection is made through the I²C port. The output current
will then match the corresponding selected current source
bank. In this case a range of 0mA to 27.5mA for SUB and
MAIN or 0mA to 102mA for CAM will be achieved.
The current sources are disabled when the block receives
an all-zero data word in both REGE and REGB2. The sup-
ply current for the block is reduced to zero. AUX 1, 2 and
3 LED outputs can be connected to CPO to turn off that
particular current source output and reduce operating cur-
rent of the disabled output to typically 10µA. AUX 4 can
be used as an open drain logic output and for this reason
will not be disabled if connected to CPO.
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