LTC3216 View Datasheet(PDF) - Linear Technology

Part Name

Description

MFG CO.

LTC3216

1A Low Noise High Current LED Charge Pump with Independent Torch/Flash Current Control

Linear Technology 

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LTC3216

OPERATION

connected between the ISET2 or ISET1 pin and GND. The

resistor values needed to attain the desired current levels

can be determined by equation 1.

RSET1/2 = 3965/ILED

(1)

A resistor value of 2kΩ or less (i.e. a short-circuit) will

cause the LTC3216 to enter overcurrent shutdown mode.

This mode will prevent damage to the part by shutting

down the high power sections of the chip.

Regulation is achieved by sensing the voltage at the CPO

pin and modulating the charge pump strength based

on the error signal. The CPO regulation voltages are set

internally, and are dependent on the charge pump mode

as shown in Table 1.

Table 1. Charge Pump Output Regulation Voltages

CHARGE PUMP MODE

VCPO

1.5x

4.6V

2x

5.1V

In shutdown mode all circuitry is turned off and the

LTC3216 draws a very low current from the VIN supply.

Furthermore, CPO is weakly connected to VIN. The LTC3216

enters shutdown mode when both the EN1 and EN2 pins

are brought low. Since EN1 and EN2 are high impedance

CMOS inputs they should never be allowed to float. To

ensure that their states are defined they must always be

driven with valid logic levels.

Thermal Protection

The LTC3216 has built-in overtemperature protection. Ther-

mal shutdown circuitry will shutdown the ILED output when

the junction temperature exceeds approximately 150°C. It

will re-enable the ILED output once the junction temperature

drops back to approximately 135°C. The LTC3216 will cycle

in and out of thermal shutdown indefinitely without latch

up or damage until the heat source is removed.

Soft-Start

To prevent excessive inrush current during start-up and

mode switching, the LTC3216 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 250μs.

Charge Pump Strength

When the LTC3216 operates in either the 1.5x mode or

2x mode, the charge pump can be modeled as a Theve-

nin-equivalent circuit to determine the amount of current

available from the effective input voltage and effective

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

ROL

+

1.5VIN

OR

2VIN

–+

CPO

–

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

ROL is dependent on a number of factors including the

oscillator frequency, flying capacitor values and switch

resistances.

From Figure 1, we can see that the output current is

proportional to:

(1.5VIN – CPO)/ROL or (2VIN – CPO)/ROL

(2)

in the 1.5x mode or 2x mode respectively.

Current Levels

The LTC3216 may be programmed to have three discrete

current levels. These are the LOW, HIGH and LOW +

HIGH current levels. The LOW and HIGH currents are set

by the resistors connected between ISET1 and ISET2 pins,

respectively, to GND. The LOW + HIGH current mode

supplies a current that is equal to sum of the LOW and

HIGH currents.

Due to the low output impedance of this part, care should

be taken in selecting current levels. This part can supply up

to 500mA continuously, and up to 1A for pulsed operation

with a 10% duty cycle. Pulsed operation may be achieved

by toggling the EN1 and EN2 bits. In either continuous

or pulsed operation, proper board layout is required for

effective heat sinking.

Mode Switching

The LTC3216 will automatically switch from 1x mode to

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

3216fc

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