LTC3208 Datasheet, PDF (9/24 Pages) Linear Technology – High Current Software Confi gurable Multidisplay LED Controller

LTC3208
BLOCK DIAGRA
C1P
C1M
C2P
C2M
31
27
29
26
V_{BAT1 30}
V_{BAT2 24}
V_{BAT3 12}
900kHz
OSCILLATOR
CHARGE PUMP
R_REF 13
DV_CC 14
ENRGBS 28
CAMHL 9
1.215V
CONTROL
LOGIC
MASTER/
SLAVE REG
SDA ₁₁
SHIFT
REGISTER
3
SCL ₁₀
ENABLE CP
MAIN CURRENT ⁴
SOURCES
SUB CURRENT ²
SOURCES
AUX CURRENT ⁴
SOURCES
CAM CURRENT ⁴
SOURCES
RGB CURRENT
SOURCES
25 GND
32 CPO
15 MAIN1
16 MAIN2
17 MAIN3
18 MAIN4
19 SUB2
20 SUB1
5 AUX1
6 AUX2
23
22
21
1
2
3
4
8
7 _{3208 BD}
RED
GRN
BLUE
CAM1
CAM2
CAM3
CAM4
AUX4 AUX3
U
OPERATIO
Power Management
The LTC3208 uses a switched capacitor charge pump to
boost CPO to as much as 2 times the input voltage up to
5V. The part starts up in 1x mode. In this mode, V_BAT1,2 are
connected directly to CPO. This mode provides maximum
efficiency and minimum noise. The LTC3208 will remain in
this mode until an LED current source drops out. Dropout
occurs when a current source voltage becomes too low
for the programmed current to be supplied. When dropout
is detected, the LTC3208 will switch into 1.5x mode. The
CPO voltage will then start to increase and will attempt to
reach 1.5x V_BAT up to 4.5V. Any subsequent dropout will
cause the part to enter the 2X mode. The CPO voltage will
attempt to reach 2x V_BAT up to 5V. The part will be reset to
1x mode whenever a DAC data bit is updated via the I²C
port or on the falling edge of the CAMHL signal.
A two-phase nonoverlapping clock activates the charge
pump switches. In the 2x mode the flying capacitors are
charged on alternate clock phases from V_BAT to minimize
input current ripple and CPO voltage ripple. In 1.5x mode
the flying capacitors are charged in series during the first
clock phase and stacked in parallel on V_BAT during the
second phase. This sequence of charging and discharging
the flying capacitors continues at a constant frequency of
900kHz.
The currents delivered by the LED current sources are
controlled by an associated DAC. Each DAC is programmed
via the I²C port. The full scale DAC currents are set by R_REF.
The value of R_REF is limited to the range of 22k to 30k.
3208fa
9