Datasheet

LTC3217
6
3217fa
BLOCK DIAGRAM
OPERATION
Power Management
The LTC3217 uses a switched capacitor charge pump to
boost CPO to as much as 2 times the input voltage up to
5.1V. The parts start up in 1x mode. In this mode, V
BAT
is
connected directly to CPO. This mode provides maximum
effi ciency and minimum noise. The LTC3217 will remain in
1x 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 LTC3217 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 5.05V. The LTC3217 will be
reset to 1x mode whenever the part is shut down.
A two phase non-overlapping clock activates the charge
pump switches. In the 2x mode the fl ying capacitors are
charged on alternate clock phases from V
BAT
to minimize
input current ripple and CPO voltage ripple. In 1.5x mode
the fl ying capacitors are charged in series during the fi rst
clock phase and stacked in parallel on V
BAT
during the
second phase. This sequence of charging and discharging
the fl ying capacitors continues at a constant frequency
of 850kHz.
EN2
EN1
CONTROL LOGIC
850kHz
OSCILLATOR
PWM TIMING
THERMAL
SHUTDOWN
LED CURRENT
SOURCES
CHARGE PUMP
ENABLE CP
4
0.8V
I
SET2
1.22V
MUX
I
SET1
V
BAT
GND2
LED4
LED3
LED2
LED1
CPO
SHORT-CIRCUIT
PROTECTION
CPO
GND1
C1P
C1M C2P C2M
3217 BD
+
–
–
+
1
15
9
10
3
11
14 16 12
13
2
4
5
6
7
8
250k
250k
–
+
+
–