Sample Project: CAN Bus Vehicle Accessory Module

• Operate from a nominal 12 V vehicle supply, surviving load dump, reverse polarity and the relevant ISO 7637-2 pulses.
• Four high-side outputs, 3 A continuous each, with open-load and overcurrent detection reported over CAN.
• CAN 2.0B at 500 kbit/s using a defined application message set; CAN-FD capable hardware for future use.
• Sleep below 100 µA with wake on CAN activity or ignition sense.
• Operating range −40 to +85 °C, parts selected accordingly.

An STM32G431 with its FDCAN peripheral pairs with a TJA1145 transceiver whose partial-networking wake keeps the module asleep until addressed. Outputs use BTS7008-2EPA dual high-side switches with per-channel current sense fed to the MCU ADC. The power input chain is fuse, reverse-blocking MOSFET and load-dump-rated TVS into a buck regulator, with a separate always-on micro-power rail for the standby domain. Ignition sense enters through a filtered, clamped comparator input.

• Input protection network validated against the selected ISO 7637-2 pulse set; load-dump energy shared between the TVS and the regulator's input rating.
• High-side switches placed on a widened-copper bank with thermal vias, keeping junction temperatures modelled inside limits at 3 A per channel at +85 °C ambient.
• Current-sense scaling chosen so both open-load (light load) and overcurrent thresholds resolve within the ADC range.
• CAN pair routed as a 120 Ω differential pair with a common-mode choke and ESD clamp at the connector.
• Automotive-qualified (AEC-Q) parts used for all silicon in the supply and I/O paths.

• FreeRTOS application: CAN task, 1 kHz output-control/diagnostics task and a background self-test task.
• Application message handling with command timeout: outputs revert to a safe state if command frames stop.
• Per-channel soft-start PWM ramp to tame inrush into lamp and pump loads.
• Fault manager latching overcurrent trips with retry policy and CAN-reported diagnostic codes.
• Sleep manager driving the TJA1145 into partial-networking standby; wake source recorded and reported.

• Bench validation of every output channel against resistive, lamp and inductive loads across the supply range.
• Supply-transient testing with replayed ISO 7637-2 pulses while monitoring CAN traffic for errors and resets.
• Sleep-current measurement across temperature corners in a small environmental chamber.
• Wake-latency measurement from CAN frame to first valid status response.
• Thermal imaging of the output bank at sustained 3 A per channel.

The prototype batch completed the bench validation plan and was handed over for vehicle-level trials, together with a findings list feeding the planned production redesign. (Fictional example outcome.)

• KiCad source files and manufacturing outputs for the prototype revision
• Firmware source with the CAN application message documentation
• Bench validation report and thermal survey
• Findings and recommendations list for the production redesign