Applying voltage to output pins

[Mohammad A]

Hi people.

I have a circuit which must enables an LDO by pressing a button which applies 4.2~3.7V to EN pin of regulator. after enabling LDO, MCU (which is from F0 series) powers on and takes control of LDO EN pin by applying a HIGH output on EN pin which is connected to MCU too.

The question I have in my mind is that is it safe to apply 4.2V to an MCU output pin which is configured to work in output mode and is set HIGH?

I have to mention that there is a resistor placed before the 4.2V so this higher voltage is not directly being seen by output pin of MCU. Will MCU sink the current of higher voltage source? Is it safe to apply a higher voltage + resistor to a set output pin?

MCU is supplied with 3.3V which is generated by LDO

[Clive1 (HNL)]

Could you use a diode?

[Ahmad M.Nejad]

When you connect high voltage (+resistor) to output pin of a MCU, the current will flow to 3.3V supply rail of the MCU.

If the current be greater than MCU consumption, it will damage MUC.

[Mohammad A]

Yes, but my question is not about circuit designation. It is about the behaviour of MCU in case of applying higher voltage on output pin

[Mohammad A]

dastet merci

[S.Ma]

Try to relook at the schematics.

Check the VIL/VIH levels for the enable pin of the LDO.

You could use a resistor divider to apply 3.3V to the LDO.

Check if you can have 5V open drain configuration

Check if you can switch from MCU being digital input to push pull output.

MCU has internal switchable resistors, you could try to activate the 50k pull down...