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ADUM6403 outputting noisy pulses instead of intended signal

Question asked by aakhmetov on Mar 21, 2018
Latest reply on Mar 22, 2018 by aakhmetov

I am using an ADUM6403 isolator to provide power and communication across an isolation barrier, with 5V VDD and 3.3V Viso. I'm sending a 4800-baud RS232 signal from the primary to the isolated side using channel A, but I'm not able to observe the same signal on the isolated side. The other three channels from the isolated side back to the primary side appear to function properly. The output of the isolator feeds a digital input pin on an IC, with very high input impedance. 


The isolator is decoupled with 1 uF || 0.1 uF capacitors on both sides of the isolation barrier. The ground pins on each side of the barrier are bonded to each other under the package:


The images below show logic analyzer captures (12MSPS) of the primary and isolated sides (I've connected the two grounds to allow the analyzer to capture both sides, but the signal appears the same way whether or not the grounds are tied together). Channel 0 shows the isolator's output (pin 14), while channel 1 shows the input to the isolator (pin 3). The images below feature a 510-ohm pulldown resistor on the isolator's output, and indicate two different timescales of the same capture. I currently don't have access to an oscilloscope due to a snowstorm in my area but I'm planning to attempt to scope the affected signals tomorrow if able.

The following image shows the same setup, but with the pulldown resistor removed.

I would appreciate it if anyone had insight as to what might cause this issue, or any other troubleshooting steps/measurements that I could take.