On 3/24/07, Orin Eman <orin.eman@gmail.com> wrote:
> http://datasheets.maxim-ic.com/en/ds/MAX6816-MAX6818.pdf
>
> Note the following statement:
>
> "Driving an input to +25V will cause
> approximately 0.32mA of current (up to 2.6mA for eight
> inputs) to flow back into the VCC supply. If the total system
> VCC supply current is less than the current flowing
> back into the VCC supply, VCC will rise above normal
> levels. In some low-current systems, a zener diode on
> VCC may be required."

It's a problem about current flow in the supply node, (or about the
supply capacity of sinking and sourcing currents as well) nothing
else.
This statement is somehow ilogic. Look why:
1. a "some low-current system" could be defined as a battery powered system
or just a low power system, powered from the main power (125V or 220V)
2. the schematic shows typical connection of input switch to ground
and not to +25V or -25V

As long you intend to use the chip in a battery powered system with
input voltage levels of +/-25V (which could be absurd in my opinion)
you just have to add more resistors in series with the 63Kohm internal
pulled up (so the sum of currents flowing to the supply node will
decrease) or to add a 5V6 zenner between the MAX power and ground pins
(assuming the supply is 5V and has no sinking features).

There is no major difference between this input circuit and PIC  input circuit.
Take a look to fig.6a. reproduce the ESD human body model to a PIC
input, apply 15KV and see will be no difference. Both PIC and MAX
device will fail.
:)
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