3.5.5.7 Blocking Diode
Another solution for low-speed signals is to use a diode and a pull-up resistor for blocking
backfeeding. The pull-up resistor must be on the same voltage domain as the IO rail of the input
side. Most SoC GPIO pins have configurable internal pull-up resistors. This can eliminate the need
for an external resistor. The advantage of the internal resistor is that it is using the correct IO rail.
The biggest drawback of this solution is that the low level of the signal is increased. Therefore,
using a Schottky diode is recommended due to the smaller forward voltage drop. Make sure the
specified maximum low level of the input pin is not violated.
Figure 79: Diode circuit for backfeeding prevention with an on-chip pull-up resistor
Figure 80: Diode circuit for backfeeding prevention with an external pull-up resistor
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