Project Status and Action Items
Worked for 1 min 27 sec
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.
I need a power switch and some output LEDs
Thought for 5 sec
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.
Worked for 1 min 54 sec
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
Run design review
Refine this doc
Ask about this doc
Input Protection Architecture Update
Decision
Rev A protection architecture is updated to avoid expensive replicated per-slot eFuse/hot-swap ICs.
Distribution board
Use one upstream PSU input protection / hot-swap / eFuse-class stage after the Bellwether HPSU connector.
This upstream stage is responsible for:
- PSU insertion/inrush management.
- Gross short-circuit protection for the shared 12 V bus.
- Hardware current ceiling for the distribution system.
- Current/telemetry output to the Pico 2 where practical.
- Power-good/fault signaling where practical.
The current schematic keeps
U_IN_EFUSE as the upstream protection placeholder. Its role was updated to reflect that it must be selected or replaced for high-current PSU classes.Boost daughterboard module
Move per-module protection onto each boost daughterboard using a module-side fuse.
The current schematic uses
FH_SLOT as the representative module-side replaceable fuse holder in the 19.5 V boost module section.This means the slot path is conceptually:
HPSU connector → upstream eFuse/hot-swap/front-end → BUS_12V → passive slot connector → module-side fuse → boost input shunt/filter/LM5122 stagePower class targets
At 12 V nominal:
Table
| PSU class | Approx input current |
|---|---|
| 750 W | 62.5 A |
| 1100 W | 91.7 A |
| 1600 W | 133.3 A |
The upstream hardware protection must be chosen for the actual maximum supported PSU and board copper/connector/thermal design. Firmware should enforce the detected PSU power budget, but firmware must not be the only safety boundary.
PMBus / firmware control
The schematic now includes placeholder Pico 2 nets for PSU capability detection:
PSU_PMBUS_SDAon Pico GPIO4.PSU_PMBUS_SCLon Pico GPIO5.PSU_PRESENT_Non Pico GPIO6.PSU_ALERT_Non Pico GPIO7.
Firmware intent:
- Detect PSU presence.
- Read PSU model/capability over PMBus.
- Determine allowed system power budget: 750 W, 1100 W, 1600 W, or safe default.
- Control module enables/modes so aggregate load stays below PSU capability.
- Optionally derate based on temperature, input voltage droop, or upstream current telemetry.
Cost / UX trade-off
Per-module fuse choices:
- Lowest cost: replaceable blade/automotive fuse on module.
- Serviceable without replacement: physical reset breaker or resettable protection, if current/thermal drop is acceptable.
- Remote reset: module-side eFuse/high-side switch, reserved for a premium/Rev B option if customers require remote fault recovery.
Per-slot distribution-board eFuses are no longer the Rev A default.
Current ERC status
After the schematic update, ERC is warning-only.
Remaining expected warnings:
- Unused/unassigned Pico GPIOs and debug pins.
U_IN_EFUSEsupport pins remain unfinished:dVdt,LDSTRT,EN/UVLO,IMON,NRETRY,RETRY_DLY,PG,ITIMER,ILIM.
Blockers before layout/order
- Select the actual upstream high-current protection architecture. A small integrated eFuse may not be suitable for 90–133 A class operation; likely options are a high-current hot-swap controller plus external MOSFETs/shunt, or a staged input protection system.
- Confirm Bellwether HPSU connector pinout, power pins, PMBus pins, present/enable pins, and Dell PSU enable requirements.
- Size module-side fuse rating against boost input current, inrush, and expected customer fault/reset behavior.
- Finish upstream eFuse/hot-swap support network and telemetry into Pico.
- Update firmware docs with PMBus power-budget policy.
Decision
Distribution board
Boost daughterboard module
Power class targets
PMBus / firmware control
Cost / UX trade-off
Current ERC status
Blockers before layout/order
