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LTC3217EUD Datasheet(PDF) 6 Page - Linear Technology |
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LTC3217EUD Datasheet(HTML) 6 Page - Linear Technology |
6 / 12 page LTC3217 6 3217f BLOCK DIAGRA EN2 EN1 CONTROL LOGIC 850kHz OSCILLATOR PWM TIMING THERMAL SHUTDOWN LED CURRENT SOURCES CHARGE PUMP ENABLE CP 4 0.8V ISET2 1.22V MUX ISET1 VBAT 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 – + + – OPERATIO 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 part starts up in 1x mode. In this mode, VBAT 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 VBAT up to 4.5V. Any subsequent dropout will cause the part to enter the 2x mode. The CPO voltage will attempt to reach 2x VBAT 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 VBAT 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 VBAT during the second phase. This sequence of charging and discharging the flying capacitors continues at a constant frequency of 850kHz. |
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