Logic Analyzer Inputs - Maximum Voltage

[jjohnson873]

I noted that the Analog Discovery 2 - logic analyzer inputs are 3.3vdc with +5volt tolerance.   The logic analyzer inputs, to the FPGA, have a 220 ohm PTC device in series with the input signal, as well as a protection diode structure to the 3.3v buss and ground.   I'm planning on testing logic signals that will go up to +6.4vdc.   With a logic level high of 6.4vdc, the protection diode will conduct current, through the protection diode, to the 3.3vdc buss and clamp the input.  Will this damage the protection diode?   The Analog Discovery 2 reference manual indicates that these inputs can support an overvoltage of +/-20v.

Should I add some input impedance between my input signal and the AD2 logic level input?

[attila]

Hi @jjohnson873

It is better to use level shifter or series resistor to limit the protection current.
Connecting such voltages to AD2 DIO directly could sink significant current and your signal level could drop if the driver can't source enough.