ESP32 and P MOSEFET

Other Hardware General Electronics
1

In a project I am up to, I have a little problem. I use ISO1540 with ESP32. While booting, ESP32 goes into brownout reset when this ISO1540 is powered (the ESP side). The goal is to turn on ISO1540 after the ESP32 boots. It works ok only when I disconnect VCC. So, how to make it by turning the GPIO on (HIGH or LOW, depends), power up the IC?

I haven't messed up with MOSFET. I have some P channel AO3415 (AO3401, too), but not sure what else should I use. From what I can see, I will need a resistor from GPIO to Gate. What resistor? What else? Can this be done this way at all?

Something like this?

Untitled2
Untitled2481×572 44.7 KB

2

To turn the MOSFET on/off your P MOSFET is up side down. :wink:

Use a circuit similar to D2 below. (transistor Q1)

Obviously your Vcc will be 3.3V

MOSFET Examples
MOSFET Examples2128×1600 433 KB

3

The giveaway is the cathode not connected to power + pin

4

So, using this schematic, with LOW on esp32_pin I can turn ON ISO1540?

Untitled
Untitled822×594 27.1 KB

The above schematic was made in a rush. I noticed later that I switched D and S. :frowning:

5

It looks technically OK to me but I find schematics confusing if the + power rail is at the bottom.

6

The reason I switched the lines at the above schematic. But pin names are the right ones. And inner circuit in the schematic part is ok.

I will check this one and let you know.

7

Ok, so while I use 3.3V on VCC1, everything goes just fine. With LOW on ESP32, I can turn one side of the ISO1540 on and off. Now, I would like to make the same for the VCC2 but there should be 5V. And this is not working. No matter the pin state, MOSFET is always letting the 5V through. I am using AO3415 btw. Besides, not much clever let the 5V on the GPIO of the ESP32. I can make a new schematic.

PS.
I believe I have to make my setup as LarryD suggested on 4th design. The one with Q10 MOSFET.

8

Indeed it will not work because, to switch a P channel mosfet off, the gate voltage has to be very near the source voltage. Search for " mosfet high side switch ".

Edit

Yes. That would be fine.

9

8050? They are similar, I think.

10

An 8050 looks fine for the npn transistor.

11

Then, this should do the job. VCC2 can be 5V and on FET2 can be 3.3V logic on ESP32.

Untitled2

PS.
I think this can be helpful for others, too.

12

R21 could just as well be 47k.

14

the mosfet is wired correctly electrically but the schematic representation is upside down.
Schematic convention has GND at the bottom and + power at the top so a p-channel high
side switch is shown like this:

p-channel high side switch
p-channel high side switch645×630 31.4 KB

15

Not a problem to try.

Agree. I was confused as well. The main thing is, this schematic is ok. The symbol is wrong orientated.

16

What is "R4" for? :thinking:

17

To discharge the input capacitance of the transistor for faster switching. :face_with_hand_over_mouth:

Which is not need in this application.

18

Will that make much difference?

(The ESP32 pulls to ground through the 1k resistor anyway.)

19

I think is just a leftover from the old days :thinking:

20

Ok, boards arrived. Everything is soldered. It works fine... sort off...

On the HIGH side of the ISO1540, I have a circuit as on post #11 of this topic. When I apply HIGH on fet2 the VCC2 passes through. When I apply LOW it doesn't. But when the board is powered off it still passes through.

This shouldn't. The VCC2 should pass ONLY if the board is powered up, and if I apply logic state on the pin. So this circuit is not what I need.

What should I change to not allow VCC2 to pass if there is no logic state on fet2? Should I connect R22 to a GND?

21

This should not be the case if the mosfet is a P channel one as you have drawn. Bringing the gate high should shut it off not make it conduct. Show a full schematic including the "ISO1540"