How to drop the voltage slightly (~100mV) for a MCU mostly in deep sleep?
Another possibility would be to have two independent connections to the supply voltage, one being used for low power mode and another one for a high power mode according to the following:

Right before driving the MCU into deep sleep mode, the active low pin _ACTIVE can be disabled (high), thus turning the PFET \$M1\$ off. This means, that the MCU will be supplied by the highly ohmic path formed by \$R_2\$ and \$R_1\$. This voltage devider must be designed to simultaneously provide a voltage smaller or equal than \$3.6V\$, and a current of approximately \$20\mu A\$ for example (just enough to keep the MCU up and running). Once you want to wake up the MCU, the pin _ACTIVE can be enabled (low) and the PFET will be turned on. Since it has a very low \$R_{DS,ON}\$, the highly ohmic path will be bypassed. The additional voltage drop that you require can be achieved by selecting a schottky diode with an appropriate forward voltage.







simulate this circuit &ndash; Schematic created using CircuitLab