[ switching 5v on off with 3.3v command ]

[texane]

Hi,

I need to switch on off a 5v source using 3.3v command (ARM MCU GPIOs).
The load can draw up to 2A, typically 500mA. In this application, frequency and
rising times can be omit (the source is switched on or off by a human).

One constraint is that the analog switch must be in serie between the source
and the load (high side design).

I planed to use a P channel MOSFET, but looking at various datasheets show
typical Vgs threshold voltages in [2 - 4]v. 2v is too close, as 5v - 3.3v = 1.7v, and
I am looking for a Vgs threshold more in the [3.5 - 4]v range, or some dedicated
IC that specifically fits this purpose ... Have you any reference?

Currently, what I do is to use a N channel MOSFET to convert the [0 - 3.3v] to
[5v - 0v] and use it to control the second P channel MOSFET. But it makes 2
FETs.

Thanks for your help!

[jmole]

Why not use a low-side switch?

[c4757p]

Currently, what I do is to use a N channel MOSFET to convert the [0 - 3.3v] to
[5v - 0v] and use it to control the second P channel MOSFET. But it makes 2
FETs.

Oh no, two FETs!

Sounds like a perfectly acceptable solution to me. Why would you rather use a dedicated IC than two cheap-ass FETs?

Why not use a low-side switch?

I second this, though. Are you sure it has to be high-side?

[texane]

Hi,

Thanks for your replies.

Being high side is a requirement in this circuit. I thought some specialized
and low cost ICs did exist for this kind of application, but the 2 FETs solution
is fine too.

[c4757p]

I'm sure there are specialized ICs for this, but it's hard to beat the price of a little FET. Out of curiosity, why high side?

[texane]

This is part of the specs: currents not returning to the ground must
also be switched off. That is why the switch is high side.

[David_AVD]

You could also check out some of the "load switch" ICs that are around.  Some of them should be in the current range you want.

[texane]

Thanks for the tip, it helps a lot. The ICs I see all have a voltage drop between
the gate and source of max. 0.2V ... it can be an issue.

[AndyC_772]

Is the pin of your MCU 5V tolerant? If so, perhaps you could pull it up to 5V with a resistor, connect it to the gate of your P-FET, and program the pin into open drain mode.

[texane]

Thanks for the advice. I will have a look at the datasheet to see if GPIOs are 5v tolerants.