Design Log DEC 011 all power rails on power module 3v3 enig serves rotor stack - thepinkmile/Enigma-NG GitHub Wiki

DEC-011 - All Power Rails on Power Module; 3V3_ENIG Serves Rotor Stack

  • Status: ✔ RESOLVED
  • Date: 2025
  • Category: Electrical
  • Area: Power Module islands, Controller Board routing, rotor stack power source

Decision

All power rails are generated on the Power Module. The Controller Board's role is purely to route power rails onward to downstream boards - it does not generate any rails itself. The rotor stack is powered by the existing 3V3_ENIG rail (TPS75733KTTRG3 LDO, 3A). There is no separate Rotor Buck; the erroneous "3.3V/5A Rotor Buck" specification was a confusion with the 5V/5A CM5 rail and has been removed.

Rationale

  • Centralising all power generation on the Power Module simplifies thermal management (all heat dissipation in one shielded enclosure with dedicated thermal zone).
  • Reduces the risk of ground loops and cross-domain sequencing issues.
  • The Controller Board as a routing layer keeps its design cleaner and easier to revise independently.
  • 3V3_ENIG (3A) covers all 3.3V consumers: CPLDs, USB-JTAG, I2C logic, control signals, and the rotor stack.
  • Settings Board RGB indicators are powered from 5V_MAIN via the Stator/Settings 6-pin harness; only their control logic remains on 3V3_ENIG.
  • ROTOR_EN (CM5 GPIO 16) enables/disables the 3V3_ENIG LDO for sequenced rotor power-up - a control signal only.

Architectural Rule (permanent)

All power rails are generated on the Power Module. The Controller Board routes rails to downstream boards only. No buck converters, LDOs, or other power-generating components belong on the Controller Board.

Impact

  • README.md: Removed erroneous "Dedicated 3.3V/5A Buck" from Controller Board section; 3V3_ENIG correctly listed as Power Module output serving CPLDs, logic, and rotor stack.
  • Power_Module/Design_Spec.md: 3V3_ENIG scope updated to include rotor stack; 3-island Power Plane retained.
  • Controller/Design_Spec.md: ROTOR_EN clarified as LDO enable signal to Power Module.
  • Rotor/Design_Spec.md: Power source updated from "Controller Board Island C" to "Power Module 3V3_ENIG rail".

Previously Conflicting References (now corrected)

  • README.md placed the Rotor Buck under the Controller Board section.
  • Rotor/Design_Spec.md said "sourced from the Controller Board's Island C".