1: is marked 'low voltage drive 2.5V' in the datasheet, so, it means its suitable to work with the 5V Vdd and logic levels from the mcu.
Yes; the logic level MOSFET’s are designed to use the logic level to completely set the N-Channel ON or the P-Channel OFF (note that they are reversed). If your P-channel MOSFET has 2.5 V switch, it means that it will completely change status to OFF when the gate is driven by 2.5 V; suitable for the 3.3V or even the 2.7V MCU operation.
2: in the case of not using the mcu, can i bypass the 100K resistor if i use a dipswitch? or i can just put the smd dipswith tied to Vdd to select manually the disabling of the circuit (i'm affraid about the max current of the typical dipsw , and as i understand i must not tie it to Vdd to switch a load that use > 200mA?
Unlike the bipolar transistor (current driven device) the MOSFET’s are voltage driven; accordingly if you provide the necessary voltage then the MOSFET will switch regardless of the current, you can directly drive the gate with DIP switch and the current will be in the Micro-Amps range.
3: i suppose you tested the pmosfet solution on real application. how problematic is the startup current peak on switching?
The inrush or peak current depends on the nature of load you are driving (inductive/capacitive); both ways; MOSFET’s as a rule has peak current values several times its continues rated current (refer to the datasheet of the selected transistor for this particular value).
I usually use the MOSFET to switch a complete section of the circuit to reduce its power consumption; not only a comparator chip, for example I can switch OFF a set of comparator; Vref, Voltage dividers, comparator pull up resistor and finally the load connected to it. Linear Technology is great but their chips are overpriced, the suggested 300 nA is priced 60 times the cost of low power version of common quad comparator.
Could you elaborate slightly on this point? I'm not sure I fully understand the point you're making. Thanks
If you checked the attached circuit; you will find that the comparator GND is equal to Vds (typical Open Drain); Voltage references will not be correct in this case and the troubleshooting will be a living hell for unaware technician to figure it out.