Re: PMOS in parallel with NMOS
- From: Rocky <RobertGush@xxxxxxxxx>
- Date: Wed, 7 May 2008 10:43:15 -0700 (PDT)
On May 7, 5:44 pm, CBFalconer <cbfalco...@xxxxxxxxx> wrote:
Tomás Ó hÉilidhe wrote:And remember too that the microcontroller that has its output floating
... snip ...
Let's say I have a PMOS and an NMOS, and I connect their gates
together. I connect the microcontoller pin to the gates.
Now, when my pin is high, the NMOS will turn on. When the pin is
low, the PMOS will turn on.
What will happen though when I set the pin to high impedence? I'm
hoping that neither transistor will be on, but I'm concerned that
maybe there might be some sort of voltage on the microcontroller
pin (it might be behind a large resistance, but it's still a
voltage) that will switch one of them on.
Just think about it. The voltage on the gate controls the
conductance. This is called transconductance, and is characterized
by the GM. That specified dI/dV at some point. However there is a
specified gate voltage for full turn-on, and another for full
turn-off. Connect two gates together and they are at the same
voltage. They are high-Z inputs, so that voltage depends on
leakage paths when not driven. If Vcc is less than the sum of the
minimum Vons both can turn off, but there is no guarantee that is
so. If Vcc is higher the odds are that both will turn on,
producing a short, and destroying at least one.
Read the data sheets. Think about the basic way FETs are
controlled.
has more than likely got inputs on that pin which are suffering the
same fate of both the hi and lo inputs turning on.
Rocky
.
- References:
- PMOS in parallel with NMOS
- From: Tomás Ó hÉilidhe
- Re: PMOS in parallel with NMOS
- From: CBFalconer
- PMOS in parallel with NMOS
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