During startup of the converter, duty cycle and peak current are limited in order to avoid high peak currents flowing from the input. After being enabled, the device starts operating. Until the output voltage reaches about 0.4 V, the average output current ramps up from zero to the programmed value, as the output voltage increases. As soon as the output current has reached the programmed value, it stays regulated at that value until the load conditions demand less current. This typically happens when the output capacitor is charged and the output voltage is regulated.
During startup, the device can seamlessly change modes of operation. When the input voltage is higher than the output voltage, the device operates in a linear mode using the rectifying switches for control. If the input voltage is lower than the output voltage it operates in a standard boost conversion mode. Boost conversion is non-synchronous when the output voltage is below approximately 1.8 V and it is synchronous if the output voltage is higher than approximately 1.8 V.
At short circuit conditions at the output, the output current is limited to the programmed average current. If the short at the output causes the output voltage to drop below 0.4 V, the average current decreases approximately linearly with the output voltage down to zero.
The devices can monotonically start into a pre-bias on the output.