I recently set up a circuit with an ADA4870 op-amp for driving an ultrasonic Piezo element. I chose this specific op-amp because it was advertised as having a slew rate of up to 2500 V/us (symmetric on rise and fall) on a 10-40V power supply. To test it I set it up with +30V for positive power, GND for negative power, and two 2.4k resistors from out to V- and V- to GND (for a 2x gain with feedback). I then fed in an Arduino digital signal set to be high for 5us and then low for 10us. The measured input waveform is a sharp step function, but the output from the op-amp looks like this:
The rise is very sharp as expected, but the fall is extremely slow at roughly 1 V/us. Normally a slow rise/fall time would make me suspect parasitic capacitance somewhere, but I can't see why that would slow down the fall time but not the rise. Does anybody have an idea of why this might be showing up?