Using TP0610 FET as a power switch

[galapogos]

Hi,
I'm trying to use a TP0610 P-channel enhancement mode FET to control
the switching on/off of a device's Vcc with an MCU's I/O pin. The
problem here is that the device's Vcc is 5.0V while my MCU supplies
3.3V only. I'm wondering if a Vgs of 3.3V will be sufficient to turn on
the FET? According to the datasheet, Vt(min) = -1.0V and Vt(max) =
-2.4V(condition:Vgs = Vds, Id = -1mA). Does that mean that it takes
anywhere from 2.6V to 4.0V at the gate to turn the FET on? If so, 3.3V
isn't very safe is it?

Also, how do I calculate how much current I should supply from my MCU
to my gate(hence calculating that series resistor value)? My device
will have a max current of ~30mA and my MCU supplies a max of 2mA.

Thanks!

 

[PeteS]

Hi,
I'm trying to use a TP0610 P-channel enhancement mode FET to control
the switching on/off of a device's Vcc with an MCU's I/O pin. The
problem here is that the device's Vcc is 5.0V while my MCU supplies
3.3V only. I'm wondering if a Vgs of 3.3V will be sufficient to turn on
the FET? According to the datasheet, Vt(min) = -1.0V and Vt(max) =
-2.4V(condition:Vgs = Vds, Id = -1mA). Does that mean that it takes
anywhere from 2.6V to 4.0V at the gate to turn the FET on? If so, 3.3V
isn't very safe is it?

Also, how do I calculate how much current I should supply from my MCU
to my gate(hence calculating that series resistor value)? My device
will have a max current of ~30mA and my MCU supplies a max of 2mA.

Thanks!

I am not sure how you are trying to implement this. I use this device
as a power switch for low current devices (Rds ~ 10 ohm).

My typical usage is

TP0610
Source -> Vcc
Gate -> 100k -> Source
and -> control
Drain -> device Vcc net

if the drive for the gate can not reach source potential (as seems the
case here), then you'll need something to assist:

I usually use a 2N7002 (or equivalent) as follows:

Drain -> TP0610 gate (control, see above)
Source -> ground
Gate -> control from processor (or whatever). I usually add a pulldown
on the gate (100k or so is usually fine) and sometimes a series
resistor if it's a high speed line or otherwise should be damped.

Now if you take the gate of the 2N7002 high, the power switch (TP0610)
will turn on.

Hope that helps

Cheers

PeteS

 

[galapogos]

I am not sure how you are trying to implement this. I use this device
as a power switch for low current devices (Rds ~ 10 ohm).

My typical usage is

TP0610
Source -> Vcc
Gate -> 100k -> Source
and -> control
Drain -> device Vcc net

if the drive for the gate can not reach source potential (as seems the
case here), then you'll need something to assist:

I usually use a 2N7002 (or equivalent) as follows:

Drain -> TP0610 gate (control, see above)
Source -> ground
Gate -> control from processor (or whatever). I usually add a pulldown
on the gate (100k or so is usually fine) and sometimes a series
resistor if it's a high speed line or otherwise should be damped.

Now if you take the gate of the 2N7002 high, the power switch (TP0610)
will turn on.

Hope that helps

Cheers

PeteS

Thanks. What does the 100K G-S resistor do? I'm not sure how the 2N7002
helps either.

 

[galapogos]

Thanks. What does the 100K G-S resistor do? I'm not sure how the 2N7002
helps either.

I tried wiring up the TP0610 with the following config
Source -> 5V
Gate -> 50K pullup to 3.3/5V -> jumper to GND
Drain -> device Vcc to a dummy load(an oscillator that draws max 30mA)

I nocied that with a 3.3V gate voltage, the "off" Vcc is something like
4.6V, which doesn't seem very "off" to me. With a 5V gate voltage
though, the "off" Vcc is lower at ~1.2V, but that still isn't
completely off. Am I doing something wrong here?

When I jumper the gate to GND, device Vcc becomes 5V which is good.

 

[galapogos]

I tried wiring up the TP0610 with the following config
Source -> 5V
Gate -> 50K pullup to 3.3/5V -> jumper to GND
Drain -> device Vcc to a dummy load(an oscillator that draws max 30mA)

I nocied that with a 3.3V gate voltage, the "off" Vcc is something like
4.6V, which doesn't seem very "off" to me. With a 5V gate voltage
though, the "off" Vcc is lower at ~1.2V, but that still isn't
completely off. Am I doing something wrong here?

When I jumper the gate to GND, device Vcc becomes 5V which is good.

OK, so I guess the 100K G-S resistor is just a pullup so that it's by
default 5V(off state)? How do you arrive at the resistor value, and
does it really matter?

Also, I tried putting a 200K pulldown resistor at device Vcc and now
I'm getting an off Vcc of close to 0V. I'm really trying to
connect/disconnect the device Vcc though, so it should be either 5V or
floating. I'm just not sure why the floating Vcc is so high when I
don't connect the pulldown.