LT3519EMS-1 데이터 시트보기 (PDF) - Linear Technology

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LT3519EMS-1

LED Driver with Integrated Schottky Diode

Linear Technology 

LT3519/LT3519-1/LT3519-2

APPLICATIONS INFORMATION

For open LED protection of a boost type LED driver, set

the resistor from the output to the FB pin such that the

expected VFB during normal operation will not exceed

1.1V. For a buck mode or buck-boost mode LED driver,

the output voltage is typically level-shifted to a signal with

respect to GND as illustrated in Figure 2. The open LED

voltage level can be expressed as:

VOUT

=

VBE(Q1)

+

R1

R2

• 1.22V

Programming the Turn-On and Turn-Off Thresholds

with the SHDN/UVLO Pin

The falling SHDN/UVLO value can be accurately set by

the resistor divider. A small 2.2μA pull-down current is

active when SHDN/UVLO is below the 1.22V threshold.

The purpose of this current is to allow the user to program

the rising hysteresis. The following equations should be

used to determine the values of the resistors:

VIN(FALLING)

=

R1+ R2

R2

•

1.22V

VIN(RISING) = 2.2µA • R1+ VIN(FALLING)

LT3519/

LT3519-1/ FB

LT3519-2

+

R1 VOUT

– 100k

Q1

R2

RSENSE(EXT)

LED

ARRAY

3519 F02

Figure 2. Open LED Protection FB Resistor Connector

for Buck Mode or Buck-Boost Mode LED Driver

VIN

R1

LT3519/

LT3519-1/ SHDN/UVLO

LT3519-2

R2

3519 F03

Figure 3. SHDN/UVLO Threshold Programming

3519fa

10

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