Rev P — Updates to Make for Next Rev

[ppannuto]

Manufacturing Concerns

• Stop/Cream apertures for custom pad shape for X2, X3 (9HT12-32.768KDZY-T) do not match metal layer.
• Consider thicker stackup
  • Confirm with MF that this won't affect microvias
  • Update RF traces

Boards with Issues / Fixes to make

• 0xA3: The board is receiving no power whatsoever...even the debugger tool isn’t registering a voltage
  • (Cause unknown currently)
• 0xAD: The board boots but fails about 90% of the time as soon as the BLE chip is enabled (prints out a debug message of “Error Detected: 0x00000007” from somewhere in the Ambiq SDK internals and then is frozen until reboot)
  • (Cause unknown currently)
• 0xAC: Board has a severe short somewhere. Switching it on causes the battery to super-heat very quickly.
  • (Cause unknown currently)
  • Notes:
    • There is a thermistor in the battery pack which will disable charging if the battery gets too warm, but discharge from e.g. a short isn't controlled currently.
    • I’ve convinced myself that PPTC is the way to go. Our concern here is really the exceptional case of a short anywhere on the board, which means that we want the protection as close to the physical battery as possible. eFuses are directional, and we’d need two to protect against exceptional situations on the charging and discharging paths, while a PPTC is a simple passive that can just intercede on the lead to the battery and cover all our bases.
  • Add PTC fuse to battery connector
• 0xA9: Board is fine but can’t find/talk to the DW3000 (UWB) chip. Same issue we saw on one of the RevMs?
  • (Cause unknown currently)

Debugging Ergonomics

• Update DW test points to be in a configuration that eases 'push and hold' debugging (either TC-10, or maybe just on a clean 50 mil spacing to match standard headers)
• Update DW/AP4 SPI test points similarly