Re: Microcontroller with 7V supply and I/O tolerance ?

From: Ulf Samuelsson (ulf_at_NOSPAMatmel.com)
Date: 10/25/04 

Date: Mon, 25 Oct 2004 10:42:04 +0200

"David" <mangled_us@yahoo.com> skrev i meddelandet
news:fdf3b9b2.0410240417.3c0d02b7@posting.google.com...
> > Since I/O is beteen 4 and 7 volts, why do you not connect the GND of the
> > Micro to 4 Volts.
> > Most CPUs will handle that.
>
> Hi Ulf, thanks for responding.
>
> I take it from your answer that Atmel don't have such a chip in their
> armoury ? I'm interested to hear from a chip mfr what the reasons
> behind this might be ? Of course I understand that CPU performance is
> all optimised for certain voltages and that device densities would
> suffer. But still... a device with a higher supply and I/O voltage
> tolerance must surely have many applications ? Anything that runs of
> batteries would be easier to design, for instance. So how about
> persuading the chaps back at base for us ? :-)

No, as others have mentioned, the cost makes the device unattractive.
To handle 7 Volt inside a transistor, you have to use processes
which are (today) totally unsuitable cost wise
Battery operated equipment is moving in the other direction to conserve
power.

Remember:

    P = C * U^2

So reduction off voltage is the most important factor in battery management.
You can use an regulator to reduce the voltage from a high voltage device.
You do not need to use the high voltage for I/O.

>
> Regards,
>
> David 

-- 
Best Regards
Ulf at atmel dot com
These comments are intended to be my own opinion and they
may, or may not be shared by my employer, Atmel Sweden.

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