SPI protection

I have a MCU board with SPI (3.3V) connector which is driven by SPI master on another board (less than 1 ft cable). What is the best form of protection for the SPI to protect from over voltages for ex connecting it to 5V SPI?

Series current limiting resistors might degrade the signal, right? Will diode clamping the SPI lines to 3.3V rail help? Having parallal schottky diodes for clamping affects signal quality at SPI frequencies? Looking at max SPI clock of 10Mhz.

Thanks in advance


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On a sunny day (Tue, 11 Nov 2014 07:40:08 -0800 (PST)) it happened snipped-for-privacy@gmail.com wrote in :

For the clock and data and CS going from the 5V board to the 3.3V you can use a resistor divider, few hunded ohms, 220 versus 330 Ohm should work, I am using that.

The other way 3.3 data to 5V board you may be in the range, else you need a buffer.

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Jan Panteltje

Many parts are designed with a N-MOSfet input protection where positive excursions are only limited by snap back of the fet. That is, there are no diodes to the positive rail. Investigate if that is the case with your part.

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