LTC3215EDD 查看數據表（PDF） - Linear Technology

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LTC3215EDD

700mA Low Noise High Current LED Charge Pump

Linear Technology 

LTC3215

BLOCK DIAGRAM

2

C1+

10

C1–

1

C2+

8

C2–

OSCILLATOR

7 VIN

EN

6

CONTROL

LOGIC

GND

9

1X MODE: CPO = VIN

1.5X MODE: CPO = 4.6V

2X MODE: CPO = 5.1V

CPO 3

VREF

MODE

CONTROL

DROPOUT

DETECTOR

ILED 4

CURRENT

SOURCE

CONTROL

ISET

5

GND

11

3215 BD

OPERATION

The LTC3215 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

this mode, VIN is directly connected to CPO. This mode

provides maximum efficiency and minimum noise. The

LTC3215 will remain in this mode until the LED current

source begins to dropout. When dropout is detected,

the LTC3215 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 re-

enabling the part.

A two phase nonoverlapping clock activates the charge

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

charged on alternate clock phases from VIN. While one

capacitor is being charged from VIN, the other is stacked

on top of VIN and connected to the output. Alternatively, in

the 1.5x mode the flying capacitors are charged in series

during the first clock phase, and stacked in parallel on

top of VIN on the second clock phase. This sequence of

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. The value of

this current may be selected by choosing the appropriate

programming resistor. The resistor is connected between

the ISET pin and GND. The resistor value needed to attain

the desired current level can be determined by Equation 1.

RSET = 3990/ILED

(1)

A resistor value of 2k or less (e.g., a short-circuit) will

cause the LTC3215 to enter overcurrent shutdown mode.

This mode will prevent damage to the part by shutting

down the high power sections of the chip.

3215fc

6

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