TPS73801: Start up questions

Hi Nanzeng,

1. Did you attach a picture under point 1? I am not able to see it. Please reattach so I can answer to that point. In general, a minimum output capacitor of 10 μF with an ESR of 3 Ω or less is recommended to prevent oscillations. Larger values of output capacitance can decrease the peak deviations and provide improved transient response for larger load current changes. This comes at the cost of large inrush current. With a sufficiently large output cap, the device can even start in current limit. At unreasonably large values of Cout, with Iout in current limit, if we have a large Vout - Vin differential, the device dissipates a lot of power which can drive the device into failure.
2. Please refer to fig 14 on the device data sheet for an understanding of this paragraph. The device has a current foldback protection mechanism which has a brickwall limit at 1.6-2A. The load line can be visualized as a straight line for a purely resistive load meets this current limit curve at one point if it is in regulation and current limit isn't reached. But if the device hits current limit, the load line MAY intersect it at two points giving two possible points of operation for the same load. The device can be brought back into regulation and out of current limit by increasing the load output impedance (increasing the slope of the load line so it intersects the graph at one point only).