LTC3214

7

3214fa

OPERATIO

2.2

µF

2.2

µF

4.7

µF

2.9V TO 4.5V

2.2

µF

ON/OFF

TORCH/FLASH

EN

LTC3214

R2

3214 F02

CPO

R1

µP

Figure 2. Recommended Circuit for Attaining Two Current Levels (Torch and Flash Modes)

oscillator frequency, flying capacitor values and switch

resistances. From Figure 1, we can see that the output

current is proportional to:

15

2

.–

–

V

CPO

R

OR

V

CPO

R

IN

OL

IN

OL

in the 1.5x mode or 2x mode respectively.

LED Current Programming

The LTC3214 includes an accurate, programmable cur-

rent source that is capable of driving LED currents up to

300mA continuously and up to 500mA for pulsed opera-

tion. Pulsed operation may be achieved by toggling the EN

pin. In either continuous or pulsed operation, proper

board layout is required for effective heat sinking.

The current may be programmed using a single external

resistor. Equation 1, used to calculate the resistor value

from the desired current level is repeated below:

For applications requiring multiple current levels, several

schemes may be used to change the resistance for the

circuit in Figure 2 uses the I/O output of a microcontroller

to switch a second resistor (R2) in parallel or series with

Mode Switching

The LTC3214 will automatically switch from 1x mode to

1.5x mode, and subsequently from 1.5x mode to 2x mode

whenever the LED forward voltage approaches the maxi-

mum CPO voltage for that mode. The part will wait

approximately 2.5ms before switching to the next mode.

This delay allows the LED to warm up and reduce its

forward voltage which may remove the dropout condition.

The part may be reset to 1X mode by bringing the part into

shutdown by setting the EN pin low. Once the EN pin is

low, it may be immediately brought high to re-enable the

part.