LTC3216

6

3216fc

BLOCK DIAGRAM

OPERATION

The LTC3216 uses a fractional switched capacitor charge

pump to power a high current LED with a programmed

regulated current. The part starts up into the 1x mode. In

provides maximum efficiency and minimum noise. The

LTC3216 will remain in this mode until the LED current

source begins to dropout. When dropout is detected,

the LTC3216 will switch to 1.5x mode after a soft-start

period. Any subsequent dropout detected will cause the

part to enter 2x mode. The part may be reset to 1x mode

by bringing the part into shutdown mode and then reen-

abling the part.

A two phase nonoverlapping clock activates the charge

pump switches. In the 2x mode, the flying capacitors are

the 1.5x mode the flying capacitors are charged in series

during the first clock phase, and stacked in parallel on

charging and discharging the flying capacitors continues

at a free running frequency of 900kHz (typ).

The current delivered to the LED load is controlled by the

internal programmable current source. Three discrete

current settings (Low, High and Low + High) are avail-

able and may be selected via the EN2 and EN1 pins. The

values of these currents may be selected by choosing

the appropriate programming resistors. Each resistor is

2

3

5

13

11

12

4

6

–

+

1

10

1.5x MODE: CPO = 4.6V

2x MODE: CPO = 5.1V

DROPOUT

DETECTOR

CURRENT

SOURCE

CONTROL

CONTROL

LOGIC

MODE

CONTROL

OSCILLATOR

8

9

7

GND

CPO

GND

EN1

EN2

3216 BD