Turn on of the LM3645 modes can be done through a combination of Control Register1, Control Register2, D_Mode Register and Strobe Control Register depending upon which mode is enabled. On start-up, when V_OUT is less than V_IN the internal synchronous P-channel MOSFET turns on as a current source and delivers 200 mA (typical) to the output capacitor. During this time the current source (LED) is off. When the voltage across the output capacitor reaches 2.2 V (typical) the current source turns on. At turnon the current source steps through each FLASH or TORCH level until the target LED current is reached unless voltage mode is enabled with the LED outputs disabled. This gives the device a controlled turnon and limits inrush current from the V_IN supply.