LTC3214EDD 查看數據表（PDF） - Linear Technology

零件编号

产品描述 (功能)

生产厂家

LTC3214EDD

500mA Camera LED Charge Pump

Linear Technology 

LTC3214

OPERATION

The LTC3214 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

LTC3214 will remain in this mode until the forward volt-

age (VF) approaches the maximum CPO voltage possible

in this mode. When this dropout condition occurs, the

LTC3214 will switch to 1.5x mode after a soft-start period.

Any subsequent dropout detected will cause the part to

enter 2x mode.

A 2-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 current is

programmed by a resistor connected between the ISET pin

and GND. The resistor value needed to attain the desired

current level can be determined by Equation 1.

RSET = 3570/ILED

(1)

Overcurrent shutdown mode will prevent damage to the

part by shutting down the high power sections of the chip.

Choosing an RSET value of 5k or greater will ensure that

the part stays out of this mode.

Regulation is achieved by sensing the voltage at the ILED

pin and modulating the charge pump strength based on

the error signal.

In shutdown mode all circuitry is turned off and the LTC3214

draws a very low current from the VIN supply. The output is

disconnected from VIN and is pulled down by a resistance

of approximately 43kΩ. The LTC3214 enters shutdown

mode when the EN pin is brought low.

Thermal Protection

The LTC3214 has built-in overtemperature protection.

Thermal shutdown circuitry will shut down the part when

the junction temperature exceeds approximately 165°C. It

will re-enable the part once the junction temperature drops

back to approximately 150°C. The LTC3214 will cycle in

and out of thermal shutdown indefinitely without latchup

or damage until the heat source is removed.

Short-Circuit Protection

When EN is brought high, the part will connect VIN and

CPO through a weak pull-up. If the CPO capacitor fails to

charge up to over 1V (i.e., CPO is shorted), the chip will

not be enabled. Similarly, during operation if CPO is pulled

down below 1V, the part will be disabled.

Soft-Start

To prevent excessive inrush current during start-up and

mode switching, the LTC3214 employs built-in soft-start

circuitry. Soft-start is achieved by increasing the amount

of current available to the output charge storage capacitor

linearly over a period of approximately 150μs.

Charge Pump Strength

When the LTC3214 operates in either the 1.5x mode or 2x

mode, the charge pump can be modeled as a Thevenin

equivalent circuit to determine the amount of current

available from the effective input voltage and effective

open-loop output resistance, ROL(Figure 1).

1.5VIN

OR

2VIN

–+

ROL

+

CPO

–

3214 F01

Figure 1. Charge Pump Open-Loop Thevenin-Equivalent Circuit

3214fb

6

Share Link: