The start-up circuit allows the COMP pin voltage to gradually increase, thus reducing the LED current overshoot and current surges. The switching operation is initiated after the COMP pin voltage exceeds 2.45 V. A 440-mV hysteresis window allows the device to operate when COMP voltage is within the expected operating range of 2.2 V to 2.7 V. Switching is disabled on detection of low COMP voltage to avoid excessive negative inductor current.

The duration of soft start, t_ss, depends on the size of the compensation capacitor and the error amplifier source current, I_COMP(SRC).

The source current, I_COMP(SRC) is a function of the transconductance, g_M, of the error amplifier and error generated between the reference and the current sensed voltage.

With no current flowing through the LEDs, the soft start duration depends on the choice of compensation capacitor, C_COMP, and the reference voltage, V_IADJ.

The open drain fault indicator, FLT, is set low when the COMP voltage deviates from the nominal range and exceeds V_COMP(OV) threshold. This setting indicates a fault condition where the converter is operating in open-loop and the LED current is out of regulation. The device can be disabled by setting IADJ input below 100 mV or controlling the UDIM input.