What is the purpose of diodes being connected here right after RC filter?


Joined Aug 21, 2008
It should be noted that the two diodes are Schottky diodes, which will have a lower forward voltage drop than the protection diodes on the input to the ADC, which would mean that the bulk of the current through R1 will go into the BAT54 Schottky diodes and very little current will pass through the input protection diodes on the ADC. If the ADC is CMOS the input protection diodes are the base-emitter junctions of parasitic NPN and PNP transistors that form to make a bipolar latch. Above some threshold current (usually 10's of milliamps for the chips I have seen) the latch turns on, shorting Vcc and Vdd pins, sometimes destroying the chip. This is often referred to as SCR Latchup.