LTC3217_15 Datasheet, PDF (6/12 Pages) Linear Technology – 600mA Low Noise Multi-LED Camera Light Charge Pumps

LTC3217
BLOCK DIAGRAM
1
C1P
14
C1M
16
C2P
12
C2M
V_BAT
15
850kHz
OSCILLATOR
CHARGE PUMP
GND1 ₁₃
CPO
2
ISET1
9
MUX
ISET2
10
EN1
3
250k
EN2
11
250k
1.22V
CONTROL LOGIC
PWM TIMING
ENABLE CP
LED CURRENT
4
SOURCES
THERMAL
SHUTDOWN
CPO
SHORT-CIRCUIT
PROTECTION
+– _0.8V
LED1
4
LED2
5
LED3
6
LED4
7
GND2
8
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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
efficiency 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
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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 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 850kHz.
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