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

From: Earl Bollinger (earlwbollinger_at_comcast.net)
Date: 10/25/04 

Date: Sun, 24 Oct 2004 21:49:21 -0500

"David" <mangled_us@yahoo.com> wrote in message
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 ? :-)
> Regards,
> David

Unfortunately for your design, the entire semiconductor world has been
shifting to smaller dies sizes, lower power contraints,
and lower voltages. Pretty soon the 1.8v systems will be common place. That
is what is driving the market now.
As for running off of batteries, many systems run off of one Lithium-Ion
cell at 3.7v quite readily.
Many other battery powered systems use one 1.2v or two 1.2v cells and use
DC-DC converters to
generate higher voltages such as for LCD back lighting and such. Thus the
old four, six and eight cell battery designs have
all been replaced by the one or two cell battery designs.
Flash card devices all run at 3.3v or less now.
So unfortunately there is simply no market for 10v MCU's anymore. The
manufacturers aren't going to make something
that doesn't make a profit for them. It costs many millions of dollars for a
factory to tool up to make the chips.
You can't make obsolete chips if no one wants them.
Even if you wanted to buy several million 10v MCU's. none of the
manufacturers would be able to accomodate you as they
have all been switching to ever smaller die sizes and equipment and no one
has old chip manufacturing facilities left to make these kind of large die
high power chips anymore.

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