LTC3208 Datasheet, PDF (13/24 Pages) Linear Technology – High Current Software Confi gurable Multidisplay LED Controller

U
OPERATIO
LTC3208
R_REF Current Set Resistor
The current set resistor is connected between RREF and
ground. The value of this resistor should typically be near
24k since all of the DAC reference currents and support
circuit currents are related to this set current.
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.
Fullscale LED Current Equations
AUX fullscale LED current (Amps) = ^1.215V • 518
R_REF
SUB / MAIN fullscale LED current (Amps) = ^1.215V • 543
R_REF
CAM fullscale LED current (Amps) = ^1.215V • 2025
R_REF
RGB fullscale LED current (Amps) = ^1.215V • 533
R_REF
Mode Switching
The LTC3208 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. The dropout
delay is typically 400µs.
The mode will automatically switch back to 1x whenever
a data bit is updated via the I²C port or when the CAMHL
pin switches from high to low.
I²C Interface
The LTC3208 communicates with a host (master) using
the standard I²C 2-wire interface. The Timing Diagram
(Figure 5) shows the timing relationship of the signals on
the bus. The two bus lines, SDA and SCL, must be high
when the bus is not in use. External pull-up resistors or
current sources, such as the LTC1694 SMBus accelerator,
are required on these lines.
The LTC3208 is a receive-only (slave) device.
ADDRESS
WR
00 110110
SUB-ADDRESS
S7 S6 S5 S4 S3 S2 S1 S0
DATA BYTE
76543210
START
STOP
SDA
0 0 1 1 0 1 1 0 ACK S7 S6 S5 S4 S3 S2 S1 S0 ACK 7 6 5 4 3 2 1 0 ACK
SCL
1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 89 1 2 3 4 5 6 7 8 9
3208 FO4
Figure 4. Bit Assignments
SDA
t_LOW
t_{SU, DAT}
SCL
t_{HD, STA}
START
CONDITION
t_HIGH
t_r
t_f
t_{HD, DAT}
t_{SU, STA}
t_{HD, STA}
t_SP
REPEATED START
CONDITION
Figure 5. Timing Parameters
t_BUF
t_{SU, STO}
3208 F05
STOP
CONDITION
START
CONDITION
3208fa
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