# Backplane

Six-slot power distribution, aggregate monitoring, CAN-FD, and cooling control.

Canonical: https://mrps.karlquinsland.com/system/hardware/backplane/
Updated: 2026-09-19

Source: https://github.com/kquinsland/modular-rack-mount-power-system/blob/f4855f0c2ca8b85eb16c4d821fcad9c6971e39fe/site/content/system/hardware/backplane/index.md


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The second-generation backplane combines the controller and six-slot power
distribution on one finalized PCB. Its outline, airflow cutouts, mounting
features, and slot locations define the mechanical design.

![Consolidated backplane, top side](<https://mrps.karlquinsland.com/system/hardware/backplane/_files/backplane.webp>)


![Consolidated backplane, bottom side](<https://mrps.karlquinsland.com/system/hardware/backplane/_files/backplane-bottom.webp>)

Generated from the committed PCB. Render provenance is recorded in [renders.json](_files/renders.json); a preview does not establish fabrication readiness.


[Interactive assembly BOM](/guides/assembly/_files/backplane-ibom.html)

## Responsibilities

- Accept the raw DC input and distribute `VIN_BUS` to six carrier slots.
- Measure aggregate input current across a 1 mΩ high-side shunt with an INA237.
- Provide a protected external CAN-FD connection and a shared bus to all slots.
- Generate local 3.3 V for control electronics and 12 V for cooling.
- Control two independent 3-wire fan power switches and read both tachometers.
- Support an externally powered DS18B20 temperature sensor.
- Drive one local status NeoPixel.
- Expose SWD for controller programming and debug.

The backplane is designed for 24–48 V nominal input. The current SW3538 carrier
limits the first population to 24 V nominal and 30 V maximum; a new carrier
revision is required for 48 V operation. Do not fit current carriers to a 48 V
bus. These design targets remain subject to first-article qualification.

Each carrier slot has four electrical contacts: `VIN_BUS`, ground, CAN high,
and CAN low. There is no backplane-to-carrier I²C bus and no per-slot logic
supply.

## Status

The finalized schematic is synchronized into a placed and routed PCB and passes
ERC and PCB DRC. Current rating, thermal performance, CAN margins, fan loading,
and protection behavior still require first-article validation.

Detailed implementation notes remain in the
[backplane README](https://github.com/kquinsland/modular-rack-mount-power-system/blob/main/hardware/boards/backplane/README.md).