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LTC3218

3218fa

BLOCK DIAGRAM

The LTC3218 uses a switched capacitor charge pump to

power a high current LED with a programmed regulated

current. Current regulation is achieved using an internal

current sense resistor connected between the CPO and

ILED pins. The part starts up in 1x mode after a soft-start

period. In this mode, VIN is connected to the CPO through

switches, the strengths of which are modulated to achieve

the desired LED current. This mode provides maximum

efﬁciency and minimum noise. The LTC3218 will remain in

–

CPO

ILED

GND

ISETF

VIN

ENT

3218 BD

CURRENT

SOURCE

CONTROL

VREF

VOLTAGE

CLAMP

106

Ω

220m

Ω

OSCILLATOR

MODE

CONTROL

GND

ISETT

ENF

CONTROL

LOGIC

OPERATION

this mode until the LED forward voltage (VF) approaches

the maximum CPO voltage possible in this mode. When

this dropout condition occurs, the LTC3218 will switch to

2x mode after a soft-start period.

The current delivered to the LED load is controlled by the

internal programmable current source. The current is

programmed by resistors connected between the ISETT

and ISETF pins and GND. The resistor values needed to

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