Micro-controller as a load
A microcontroller's "load" varies depending on what you're doing on it. This means that if you're taking it as a resistive load. The resistance changes as the power it draws changes. This is a very hard question to answer, however I would recommend going to the specific MCU data sheet, finding it's maximum power consumption and also find the block diagram and base the load and impedance on the first block relating the the power input