We had to make some component substitutions and PCB layout changes due to the supply chain issues, and due to lack of availability, substituted the ADUM5402ARWZ we have been using successfully for years with ADUM6402CRWZ. We did have to make small adjustment to the Viso pin PCB layout connections, but are still using the same capacitors in the same locations as with the ADUM5402ARWZ (2 x 0.1uF X7R 0603 MLCC caps, 1x 0.01uF X7R 0603 MLCC directly near Pin#16, and 1 x 10uF X7R 1206MLCC cap directly under (opposite PCB side) of the other capacitors with multiple vias connecting to the power plan and the Viso pin trace. I realize this may have been considered 'marginal' but it worked very reliably with the ADUM5402ARWZ for years.
Now, with ADUM6402CRWZ in place, we added a jumper wire (short) from Pin#7 to Vdd 10uF capacitor - it is less than 15mm long.
From a sample size of (12) complete printed circuit assemblies we observe approximately 40% working acceptably. The remainder seem to exhibit either a Viso regulation problem (regulation begins at 5.0V, becomes unstable and ends up regulating at 4.7V) - OR- Viso appears to regulate OK at 5.0V (Vdd input at Pin#1 is also 5.0V) but we observe strange oscillations/glitches on one or more of the data pins, even when no data signal is being applied. It can appears are triangular, RC type-decay type waveforms on the Viso pins, and correspondingly as data glitches on the Vdd data pins, often with the signal level going from 5.0V to 2.5V or from 0V up to 2.5V.
From looking at other threads on the forum, maybe it is somewhat of a PCB layout issue for regulation - but the ADUM5402 didn't seem to have an issue. And, it appears at least some of the ADUM6402 seem to be OK with it. But the cases of the oscillation/noise glitches appearing even when the Viso output appears to be glitch free and stable is very confusing.
I can attach more images if needed. Here are a few to illustrate what we see on the problematic units.
Component info: ADUM6402CRWZ #2049* 5129927.1 Vdd = 5.0V, Viso = 5.0V
Viso regulation glitches/level shifts
Viso ends up regulating at 4.7V
2nd -issue mode, Viso seems to regulate OK, but noise/oscillations appear on data channels on device:
Viso regulating at 5.0V
Pin #11 oscillatory noise with no data being driven into it:
resulting glitches appearing on data channels pins # 6,5,4 - note that it drops from 5.0V to approx 2.5V
On the oscillatory units I have also tried increasing Viso capacitance to 20uF, but still the problem persists. On some PCAs we have tried replacing the ADUM6402 with another, but as we seem to have less than 50% success rate to begin with, that hasn't usually solved things either.
Any additional help you can provide is much appreciated - Thank you!
Mike
