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3.3V 20mA and 1amp tied together and need switching

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Full Member level 6
Aug 1, 2009
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I have two power source
3.3V/20mA and

I can control 3.3V/1amp ON/OFF while 3.3V/20mA is always ON

These two are tied together and voltage goes to microcontroller.

3.3V/1amp goes to other peripherals too... Like LCD, switches, and some other devices.

Note: 3.3V/20mA (in series with 3.3V/1amp) is only connected to MCU

Operation details are as follows

when 3.3V/1amp and 3.3V/20mA are tied together, all the devices are ON and everything works properly.

What I need is

There are certain situations where MCU should turn off the 3.3V/1amp and go in sleep mode operating on 3.3V/20mA

In this sleep mode, all peripherals should be off (ie 3.3V/1amp should be disconnected to all teh devices beyond MCU

I am trying to have a p channel MOSFET to do the switching but due to the internal diode seems to create some issues ( I donot want 3.3V/20mA to power any other devices beyond MCU)

How can I achieve this switching.

Hope my explanation was clear :)

Attached is the image for what I am trying to do.


    6.6 KB · Views: 77


you hard connected both 3.3V/20mA and 3.3V/1A. So they are tied together. forever.

What you need is to seperate both supplies and use intelligent power switching.

Look for "ideal diode", "backup battery switch", "power distribution switch", "power switch", "hot swap power controller".. in the given order.

Ideal diode could be useful for uController.


I can control 3.3V/1amp as there is a EN pin for the converter.

But because 3.3V/20mA is tied together with 3.3V/1amp, 3.3V/20mA will flow to the ON/OFF control and if I use a p MOSFET, there will be a internal diode and that same voltage with the drop will go to peripherals.

Ideal diode, I am not too sure if there is anything as ideal but a few mV drop should be fine. Can you suggest any part ???

I am already using the PMIC that can charge battery, switch betteen input of USB and Battery and has a 3.3V/1amp buck boost whose ON/OFF is controllable and 3.3V/20mA which is always ON

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EDIT: P Diode will come into picture only when its turned off by the MCU pin ofcourse :)

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EDIT AGAIN: Its P MOSFET and not P DIODE... Sorry for the typing mistake


there are devices called "ideal diode". That´s why i said you should look for it.


The categories of parts KlausST was getting at will be able to block current in both directions.

With discrete parts the way to do that is to have two mosfets back to back with the sources connected. This will block in both directions and works with either P's or N's.

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