Help me Understanding the PMOS selection to turn one 5v load with 3.3v logic

I am saw a lot of post explaining this but i don't quite understand it. I am using a ESP32 and it works on 3.3v and i need to turn on 2 thing that works on 5v and another on is lithium-on battery that works on 2.8v~4.2v. So i have to use PMosfet to do it, and one that i used is only works on 5v logic. So i saw people are suggesting to use a PMOS that's RDS, ON for voltages of 3.3V or less. I see nothing on the mouser to search. I see only one with resistant but i need the voltage.

https://www.mouser.com/Semiconductors/Discrete-Semiconductors/Transistors/MOSFET/_/N-ax1sf?P=1y95l6eZ1z0y3dtZ1yikk48

I can suggest this one, available at Digikey & Mouser https://www.diodes.com/assets/Datasheets/DMP2045UQ.pdf You don't say what current you are switching.

Use a pullup resistor on the gate to the 3.3V or higher source voltage to turn it off.

Use an N-channel MOSFET such as FDN327N to pull the P channel gate low, and drive the N-channel gate from the ESP32 3.3V output.

Thanks fro the suggestion, but i am trying to understand how to select one. My current for the load is not more then 500~700 amp.

500 to 700 amp? Did you mean milliAmp?

Yes. And i have to use only one PMOS as the pcb is already ordered and i don't want to extend the parts list.

I am already using this mosfet https://www.mouser.com/datasheet/2/427/si2301cd-1765174.pdf in this configuration But it's not turning on with the 3.3v logic, BAT+ is 5v, it's not a battery.

Looks like it should work. How are you wired up?

Vishay Siliconix part.JPG|1040x65

P-channel MOSFET, with N-channel to drive Gate.JPG|676x383

As i said i don't want use another part like the transistor. that part is not working, i already tested it. this my circuit i can't upload pic here https://ibb.co/bv8k0LH

Okay; I know my circuit works, I have it running to power down an LCD screen and other bits of the board for power saving. Only the ESP32 remains, in deep sleep, and a button with pullup resistor to wake it up by connecting a pin to Gnd.

You have not shared your circuit, so we can't really tell what you have going on.

https://ibb.co/d5h3cKy

https://www.mouser.com/datasheet/2/427/si2305cd-1764559.pdf

now i am trying understand the RDs thing, but i can't. as i see from my need, 5-3.3 = 1.7v for the load and 4.2~3.7- 3.3= .5v, RDs should be less then 1.7v at lest? i am not sure at all.

The specification give RDS(on) in OHMS at a given gate to source voltage (VGS).

The circled spec shows RDS(on) = 0.065 Ohms at gate-source voltage of -1.8V, which is fine for your purpose.

i can't upload pic here

Yes, you can, and please do that in the future. In the post editor, click the Preview button > Attachments and Uploads > upload the photo.

CrossRoads: Okay; I know my circuit works, I have it running to power down an LCD screen and other bits of the board for power saving. Only the ESP32 remains, in deep sleep, and a button with pullup resistor to wake it up by connecting a pin to Gnd.

I know it will work, but i don't want to add more part to my circuit. Before i used pro micro board nad it was 5v and with one PMOS i could do the truing off the load.

Rds is the on-resistance when the gate is a lower voltage than the source (which is why Vgs is shown as a negative number). In my circuit, the Source is 3.3V, the Gate is pulled down to nearly 0V by the FDN327N, so Vgs is greater than -2.5V (approaching -3.3V) and the part fully turns on, so the Drain goes to ~3.3V. With 500mA and Rds = 0.05ohm, the output would be 3.3V - (0.5A x 0.05ohm) = 3.25V.

You can do similar math for your part. And show your circuit.

If you are using Windows, then Start Menu:Windows:Accessories:Snipping Tool is handy for grabbing sections of a screen, adding a note, saving, and then attaching here in the forum. I have it on my Task Bar and use it a lot.

This is my circuit

Screenshot 2021-02-28 010456.png|289x478

And POWER_LED swings between 0V (for LCD_5V = on) and 3.3 (for LCD_5V = off)?

yes.

That should work. Are you sure the mosfet is connected correctly? Did you connect the gnd of the 5v supply to the gnd of the esp32?

Exactly how does this not work? Always 0 volt output? Always 5v? Please provide detail.

I don't know, i tested the mosfet gate, and esp32 is putting 3.3v and gnd correctly. but the mosfet does not cut the power i mean does not turn off, ( 5v to 0v).

here is the schematics, https://gitlab.com/mutantC/mutantc-v4/-/blob/master/Schematic_mutantC_v4.2.pdf

1) You have 5 p-channel switches shown. Do any of the 5 work correctly? 2) Are the grounds of the supplies you are switching connected to the esp32 ground?