Datasheet LT3519, LT3519-1, LT3519-2 (Analog Devices) - 10

LT3519/LT3519-1/LT3519-2
APPLICATIONS INFORMATION
For open LED protection of a boost type LED driver, set
Programming the Turn-On and Turn-Off Thresholds
the resistor from the output to the FB pin such that the
with the SHDN/UVLO Pin
expected VFB during normal operation will not exceed The falling SHDN/UVLO value can be accurately set by 1.1V. For a buck mode or buck-boost mode LED driver, the resistor divider. A small 2.2μA pull-down current is the output voltage is typically level-shifted to a signal with active when SHDN/UVLO is below the 1.22V threshold. respect to GND as illustrated in Figure 2. The open LED The purpose of this current is to allow the user to program voltage level can be expressed as: the rising hysteresis. The following equations should be V used to determine the values of the resistors: OUT = VBE(Q1) + R1 • 1.22V R2 VIN(FALLING) = R1+R2 •1.22V R2 V IN(RISING) = 2.2µA • R1+ VIN(FALLING) + RSENSE(EXT) R1 VOUT LED VIN – ARRAY 100k Q1 R1 LT3519/ LT3519/ LT3519-1/ FB LT3519-1/ SHDN/UVLO LT3519-2 LT3519-2 R2 R2 3519 F02 3519 F03
Figure 2. Open LED Protection FB Resistor Connector Figure 3. SHDN/UVLO Threshold Programming for Buck Mode or Buck-Boost Mode LED Driver
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