Datasheet AL5814Q (Diodes) - 9

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AL5814Q Application Information
(continued) VIN LED1 LED2 OUT
T
Q1 Q2
UC OD
FB
R P W
RS1 RS2
E N Figure 4. Two LED Strings in Parallel
The output current can be set as: I𝑳𝑬𝑫𝟏 = I𝑳𝑬𝑫𝟐 = ⋯ = 𝑉𝐹𝐵/𝑅𝑆1 Where ILEDx is the desired LED current, VFB is VVSET, and RS1 is the sense resistor. To keep the LED currents as equal as possible, transistors Q1 and Q2 must be matched, and RS1 and RS2 must be matched.
Open Load Detection SFAULT Setup:
The AL5814Q can be configured to detect the presence of the LEDs on the external output transistor going open circuit. This function is activated by the SFAULT pin. A 50µA current source from SFAULT creates a voltage (VSFAULT) across an external resistor (R7), which is compared to potential divided down VCC voltage. See Figure 5 (blue components are internal to the AL5814Q).
Figure 5. SFAULT Configuration
Once VCC rises above the set voltage on the VSFAULT pin, the EN_FAULT becomes high, and LED-open detection becomes functional. This avoids false triggering of open-load protection during startup and powerdown procedure. Supply voltage where LED-open detection becomes operational is set by the following equation: 𝑉𝐶𝐶 = 11 × 50 × 10−6 × 𝑅7 AL5814Q 9 of 14 April 2019 Document number: DS41792 Rev. 1 - 2
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