CC3220: System restart

Part Number:CC3220

Hi Team,

   My customer use CC3220SF and the project move to PP. They made 10 sets of prototypes, 3/10 met system restart issue.

   1. When do AB/BA test, the failure comes with CC3220SF.

   2. When the happens, the voltage of PIN33, VDD_PA_IN is frequently pulled down, which is the same with system reset cycle. The waveform is as below.

3. When use external DC/DC to supply 3.3V VIN with high current capability, the issue is the same.

4. The design is similar with CC3220SF-LAUNCHPAD.

So my question is:

1. What will cause this frequencly voltage drop in VDD_PA_IN pin?

2. Can external DC/DC supply directly to DCDC_PA power rail?

3. Any other suggestions or tests we can do?