AD7656BSTZ-1 Popping problem

Our company had been using AD7656BSTZ-1 for years and there was not any problems until June 2019 when the first popping problem happened, what’s worse, another three cases came out one by one from July 2019 to January 2020, and the popping problem could happens even without any input of any sampling channel. Figure1 is a burst one after a popping with smoke, the four burst chips’ SN are #1524, #1524, 1504, #1428.

We have listed 4 clues as below after schematic checking, but we are not very sure whether or not we have exactly located the root causes, so we’ll deeply appreciate it if we could have ADI’s professional confirmations and explanations.

  1. The historical chips works well in our old product which I name it Rack V1, the four popping cases only happened in our new product which I name it Rack V2, and the popping phenomenon occurs only at the moment Rack V2 powers on.
  2. There is a big change of the ±15V switching power supply from Rack V1 to Rack V2, as shown in Figure2, which leads to a clear difference on the powering up sequence and timing, as shown in Figure3 and Figure4.
  3. The |AGND-DGND| does not meet the ABSOLUTE MAXIMUSM RATINGS which limit it must not exceeds 0.3V, but we found it does exceeded 0.3V for a short time after we captured the wave form of |AGND-DGND| as shown in Figure5.
  4. There are no Schottky diodes in our design at the VDD and VSS pins as recommended as “Power Supply Configuration” in user manual Rev. D.

P.S. Figure3 was plotted according to Figure6 and Figure7, for limited probes to capture all the wave forms in one time.

P.S. Figure4 was plotted according to Figure8 and Figure9, for limited probes to capture all the wave forms in one time.



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[edited by: @skowalik at 8:04 PM (GMT 0) on 2 Mar 2020]