Design Log DEC 048 esd protection extended to host side rotor facing btb connectors - thepinkmile/Enigma-NG GitHub Wiki

DEC-048 - ESD Protection Extended to Host-Side Rotor-Facing BtB Connectors

  • Status: Approved
  • Date: 2026-04-30
  • Category: ESD / Protection Strategy
  • Area: Stator, Extension, Reflector - Rotor-Facing BtB Connectors
  • Author: Izzyonstage & GitHub Copilot

Summary

ESD protection requirement (DEC-045) has been extended from the Rotor board to all host-side boards that present rotor-facing BtB connector faces during live rotor swap. Any exposed Samtec ERM8/ERF8 connector face that is accessible when a rotor is being inserted or removed must carry TVS protection.

Problem

DEC-045 mandated TPD4E05U06QDQARQ1 ESD arrays on the Rotor board side of each BtB interface. However, when a rotor is extracted, both the rotor-side connectors and the host-side (Stator / Extension / Reflector) socket faces become simultaneously exposed to operator handling. An ESD event from operator touch to the host-side socket during live swap would propagate directly into the host board with no protection.

Decision

All Samtec ERM8/ERF8 connector faces on host boards that are exposed during live rotor swap require a TPD4E05U06QDQARQ1 4-channel bidirectional ESD array within 3mm of the connector mating edge. Only JTAG and ENC signal connectors are in scope; Power connectors (power-only BtB pairs) and all internal IDC/ribbon/harness/dock connectors are explicitly excluded.

Board-level implementation:

  • Stator: U9 (J1 JTAG), U10-U12 (J3 ENC) - 4 arrays total.
  • Extension: U2 (J1 JTAG in), U3-U5 (J3 ENC in), U6 (J4 JTAG out), U7-U9 (J6 ENC out) - 8 arrays total.
  • Reflector: U1 (J1 JTAG), U2-U4 (J3 ENC) - 4 arrays total.

Internal connectors explicitly excluded from this decision:

  • All power-only BtB connector pairs on any board.
  • Stator J4-J13 (IDC encoder ports, Extension Port ribbon, Controller docks, Settings harness).
  • Extension J7/J8 (Extension Port BHR-20-VUA ribbons) and J9/J10 (AM service docks).
  • Reflector J4 (TTD_RETURN ribbon).

Rationale

Rotors are a user-handled, hot-swappable component. During installation or removal, both sides of the connector interface are simultaneously accessible. Protecting only the rotor side is insufficient - a real ESD event from an operator to an unprotected host socket would destroy the host board as readily as a rotor. Extending the same TPD4E05U06QDQARQ1 device used on rotors to the host-side connector faces closes the remaining ESD risk at minimal BOM cost (16 additional arrays across 3 boards).

Impact

  • design/Electronics/Stator/Design_Spec.md: Added FR-STA-13, DR-STA-16; §8 ESD section rewritten; BOM U9-U12 added.
  • design/Electronics/Extension/Design_Spec.md: Added FR-EXT-07, DR-EXT-13; §5 ESD section rewritten; BOM U2-U9 added.
  • design/Electronics/Reflector/Design_Spec.md: Added FR-REF-05, DR-REF-06; §5 renamed to Thermal & ESD; BOM U1-U4 added.
  • design/Electronics/Consolidated_BOM.md: Section 1 and Section 2 updated.

Cross-ref

DEC-045 (Rotor ESD), design/Electronics/Stator/Design_Spec.md §8, design/Electronics/Extension/Design_Spec.md §5, design/Electronics/Reflector/Design_Spec.md §5.