Marechiare wrote:
> The main advantage is that it references to the input's chip Vdd. The
> gap for logic "1" input voltage is quite narrow. With the divider you
> are risking to either overvoltage input or just not reach the logic
> "1".

Not really in a typical case.  Let's say we have a nominal 5V +-2% (just
about any LDO can do that) input and are using 5% resistors, 2Kohms followed
by 3.9Kohms to ground.  The worst case high output is 5.1V into a
1900ohm,4095ohm divider, which comes out to 3.48V.  The worst case low is
4.9V into 2100ohm,3705ohm divider, which comes out to 3.13V.

Let's again say we're using a 2% LDO on the 3.3V side, so it can range from
3.37V to 3.23V.  About the highest logic high threshold you'll encounter is
80% of the supply, which is what PIC inputs with Schmitt triggers have.  The
worst case logic high threshold is therefore 3.73V * 0.8 = 2.69V.  That's
still significantly less than the lowest high of 3.13V computed above.

On the other end, the highest high of 3.48V is only 250mV above the lowest
possible Vdd.  There won't be any meaningful current thru any protection
diode at 250mV.

If you really care you can use 1% resistor, which nowadays cost the same as
5% anway.


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