Datasheet AL5814Q (Diodes) - 10

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AL5814Q Application Information
(cont.)

The table below shows approximate supply voltages where the LED-open detection becomes active by different resistor values. VCC (V) R7 (kΩ) 5.01 9.1 5.50 10 6.60 12
T
8.25 15 9.90 18
UC
11.55 21
OD R
If SFAULT is shorted to GND, by default LED-open fault detection is automatically entered. If SFAULT is left open, LED-open detection is inhibited.
P W VFAULT E
The AL5814Q detects open conditions on the collector/drain of the external transistor driving the LEDs using the VFAULT pin (see Figure 6). The
N
VFAULT pin has a 14µA current source generated out of this pin.
Figure 6. LED-Open Detection Using VFAULT
If the LED string is open, VFAULT pin is pulled down by the power bipolar or MOSFET below its internal 2.5V threshold. This condition triggers an output disable condition causing OUT to go low, turning off the external MOSFET/BJT. A resistor (R3, 100K) is required to keep the VFAULT signal low during a fault condition. A 100kΩ keeps this node low. When the fault condition is fixed, and VFAULT pin rises above 2.63V, the device operates normally.
Feedback Loop
The device has internal compensation; therefore, it is not recommended that any components are added to the feedback loop.
LED Thermal Compensation
The LED current is set by the reference voltage at the emitter/drain voltage of the LED driving transistor. This reference voltage is determined by the resistor divider between REF and VSET. The LED driver’s LED current behavior under different ambient or LED temperatures can be configured by using NTC for R6 shown in Figure 7. AL5814Q 10 of 14 April 2019 Document number: DS41792 Rev. 1 - 2
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