Project Status and Action Items

K

kproc

Good job rotating the connectors. Delete CN1. I also want to move the Pico to the top of the board

flux

I’ll remove the extra CN1 connector and move the Pico module up toward the top edge of the PCB, then verify the placement.

flux

Done. I deleted CN1 and moved U_MCU/Pico to the top of the board; it is now centered at about (10 mm, 88 mm) with its top edge just inside the board outline.
Open item: the Pico was clamped at the board edge, so if you want more clearance from the top edge I can drop it slightly lower.
K

kproc

I need a power switch and some output LEDs

flux

I’ll add a low-current front-panel power/enable switch rather than a high-current 12 V path switch, plus output/status LEDs with current-limiting resistors, then verify the schematic changes.

flux

Added the power switch and output LEDs. SW_PWR is a low-current front-panel switch that pulls Pico 3V3_EN to GND to turn logic off, and I added green indicators for BUS_12V and VOUT_19V5 with 4.7kΩ and 8.2kΩ series resistors.
Open items:
  • These are placed near the top/front-panel area but not routed yet.
  • If you intended a true high-current input disconnect instead of a Pico enable switch, that needs a different switch/contactor architecture.
Route controls and verify
Use high-current switch
Route switch and LEDs
Add LED labels
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Schematic

Layout

Preview

Rev A Architecture Plan — Rackmount 12V Distribution PSU
Build Rev A as a single-PSU 12V distribution controller/backplane with a target of 12 physical boost-module slots, while accepting that mechanical/thermal analysis may reduce the first build to 8–10 slots. Rev A defers Ethernet and dual-PSU HA/failover.
Top-Level Architecture
Diagram



  
    
  
  
    
  


















"Dell D750E-S1<br/>12V node_65A"
"Bellwether 70012-1111<br/>custom/imported HPSU input"
"Input protection<br/>bulk caps<br/>total current sense"
"12V high-current bus"
"Target 12 protected edge slots<br/>switch / fault / enable"
"LM5122 boost daughterboards<br/>local current/temp monitoring"
"Pico 2 / RP2350 control"
"system status LED"
"USB/UART/SWD debug"
Key Decisions
PSU Input
  • Use Bellwether 70012-1111 for Dell D750E-S1.
  • User supplied product page, package spec, documentation, and 2D drawing.
  • Create/import a custom connector part and footprint from the Bellwether files before layout.
  • Verify Dell D750E-S1 pinout before wiring sense, PS_ON, present, or current-share pins.
  • Add total input current sensing if practical, but do not rely on INA3221 on the distribution board for per-slot telemetry.
Slot Count
  • Aim for 12 daughterboard connectors.
  • Expect possible reduction to 8–10 after mechanical/thermal layout because the slot bay next to one PSU is only about 157.5 mm wide.
  • Firmware budget remains based on one 750W PSU, not 12 simultaneous 180W outputs.
Per-Slot Power Switching
Preferred implementation:
  • Per-slot high-side protection/eFuse/hot-swap/load-switch stage sized for the actual ~16–20A worst-case 12V slot current.
  • MCU enable control per slot.
  • Fault output per slot if the selected protection device supports it.
Avoid relying on only a discrete MOSFET plus firmware for short-circuit protection. The previously listed TPS25952x-class part may be undersized and needs replacement or architectural adjustment.
Current and Efficiency Monitoring
  • Distribution-board INA3221 is dropped from Rev A direction.
  • Prefer per-daughterboard current monitoring so each boost module can report both input and output current for efficiency calculation.
  • Cost-driven default: two INA181 current-sense amplifiers per daughterboard, one on the 12V input side and one on the 19.5V output side.
  • Alternative: one distribution-board per-slot input current sensor plus one daughterboard output sensor, but this complicates harnessing/backplane analog routing and is less modular.
  • Two-channel current monitor ICs remain possible but are currently less attractive due to JLCPCB cost.
LM5122 Mode Control
  • Keep a MODE control signal to allow firmware-assisted efficiency optimization if the LM5122 implementation supports practical CCM/DCM or efficiency-mode control.
  • UVLO and hardware safety thresholds stay local to the daughterboard.
  • Firmware may adjust mode based on measured output current, but hardware protection must remain independent.
MCU / Ethernet
  • Ethernet is deferred to Rev B.
  • Raspberry Pi Pico 2 / RP2350 remains acceptable for Rev A control, slot enables, status LED, fault logging, and USB/debug access.
  • Leave expansion path for future W5500 or other Ethernet control-plane hardware.
Edge Connector Boundary
  • User-selected 32-pin connector has stated 3A/contact rating.
  • Existing allocation with 10 VIN and 10 GND pins gives 30A theoretical per rail side; this is enough for a ~16–20A slot with margin if temperature rise and contact imbalance are acceptable.
  • Drop separate AGND for now; use single GND plus careful Kelvin/current-sense routing on the daughterboard.
  • Add status/control pins including EN, MODE, FAULT, PGOOD, current telemetry, temperature telemetry, VOUT sense, and at least one module-present/ID/spare signal if pin budget allows.
Boost Module Boundary
The supplied LM5122 BoM is the daughterboard power-stage candidate. The main rack board distributes 12V and control/status signals; current/temperature monitoring is primarily local to each daughterboard.
Required New Components Not Yet in Current Schematic
  • Bellwether 70012-1111 custom/imported HPSU connector.
  • Per-slot protection devices sized for ~16–20A/slot.
  • 12 edge connectors, subject to mechanical feasibility.
  • MCU support passives and programming/debug access.
  • Logic rail regulator, likely 3.3V.
  • System status LED.
  • Slot fault/enable interface components.
  • Test points.
  • Input bulk capacitance, transient protection, and optional precharge/inrush components.
Deferred Features
  • Dual PSU ORing.
  • Active-active current sharing.
  • Hot-swappable PSU redundancy.
  • Ethernet / Prometheus / web UI.
Schematic Implementation Order
  1. Create/import Bellwether connector and confirm Dell D750E-S1 pinout.
  2. Choose final slot count candidate and edge connector pitch based on preliminary chassis layout.
  3. Select final per-slot protection/eFuse/hot-swap solution sized for slot current.
  4. Implement one distribution-board slot block: edge connector, enable, fault, protection, status/test points.
  5. Implement one daughterboard monitoring/control block: two INA181 stages, thermistors, MODE/EN/FAULT/PGOOD/VOUT sense.
  6. Add Pico 2 control, status LED, debug, 3.3V logic power.
  7. Replicate slots only after one slot/daughterboard interface is reviewed.
Open Questions
  • Can 12 vertical daughterboards fit with adequate airflow in the 157.5 mm bay, or should Rev A target 8–10?
  • Which per-slot protection part can meet ~16–20A with JLCPCB availability and acceptable thermals?
  • Should each daughterboard have a small local ADC/MCU/digital telemetry, or should analog telemetry return to the distribution-board MCU?
  • How should the rear DC barrel connectors mechanically mount: directly on daughterboards, panel-mounted with pigtails, or daughterboard-mounted through rear slots?

  • Recommended Rev A Scope

  • Top-Level Architecture

  • Key Decisions

  • PSU Input

  • Slot Count

  • Per-Slot Power Switching

  • Current and Efficiency Monitoring

  • LM5122 Mode Control

  • MCU / Ethernet

  • Edge Connector Boundary

  • Boost Module Boundary

  • Required New Components Not Yet in Current Schematic

  • Deferred Features

  • Schematic Implementation Order

  • Open Questions