PMOS replacing

[snx]

In a microcontroller application, it is desired to power off a 3V3 DCDC converter and all the follwoing devices for saving power. The MCU must be kept alive for simple tasks which not require external devices. For this a 1V8 regulator is used. Also, if the input voltage is insufficient for the dcdc, the device will still run from the 1V8 regulator.

For this i found an application note from ST, that lets you switch between two coin cells.  They are using the P-Mosfet STS5PF30L. Sadly, this mosfet comes in SO-8 which uses up alot of board space if two are used one is almost the size of my mcu!! .  Also its expensive.

As a similar replacement i want to use the CSD25310  from TI.

Attached you can find the ST app note for two coin cells, and the changes that i would use.

Would this wort with a 3V3 and 1V8 Source and my mosfet of choice?

[Wimberleytech]

Appears to me it would work.  The TI mosfet has a lower threshold which is good since you are also lowering one of the cells.

[Someone]

Some regulators allow you to eliminate the extra switches:
https://e2e.ti.com/blogs_/b/powerhouse/archive/2014/08/26/how-to-improve-buck-converter-light-load-efficiency-with-an-ldo-part-1

[snx]

Yes i'm aware of this circuit. In my case, on the DCDC there are alot of devices (NFC Reader, Motor Drivers etc) all with a shutdown current of a few uA. If they are all kept on power, the current sums up to about 20uA

In my application, the DCDC will be shut down completely, and ONLY the mcu will receive the 1V8. The rest of the parts are not supplied, to get maximum battery life. Even if i would power all devices with 1V8, it would operate multiple devices out of their reccommend specs. So this is sadly no solution for my problem,  i need to have mosfet.

[Someone]

Yes i'm aware of this circuit. In my case, on the DCDC there are alot of devices (NFC Reader, Motor Drivers etc) all with a shutdown current of a few uA. If they are all kept on power, the current sums up to about 20uA

In my application, the DCDC will be shut down completely, and ONLY the mcu will receive the 1V8. The rest of the parts are not supplied, to get maximum battery life. Even if i would power all devices with 1V8, it would operate multiple devices out of their reccommend specs. So this is sadly no solution for my problem,  i need to have mosfet.

If the 1V8 regulator is only powering your mcu, then you need a power switch for the other (3V3) supply or possibly just a low voltage diode. But the switch on the 1V8 supply may be redundant depending on the 1V8 regulator you use.