Comma.ai Panda Board
Thought for 5 sec
Use TI TCAN3404-Q1 for each of the three CAN channels.
Why it fits:
- CAN FD: supports data rates up to 8 Mbps
- Automotive qualified: AEC-Q100
- 3.3 V MCU interface: compatible with the STM32H725
- Wide bus fault protection: ±58 V
- Low-power standby mode
- Small VSON package: suitable for the 85 × 50 mm board
Recommended orderable part:
- TCAN3404DRBRQ1
- Package: 8-pin VSON/DRB, 3 × 3 mm
- Quantity: 3
Use one TCAN3404-Q1 per channel, followed by the channel’s common-mode choke and PESD2CAN protection. Verify that the footprint includes the exposed thermal pad and connect it to ground with nearby vias.
Recommand NXP product
Thought for 14 sec
I recommend the NXP TJA1044GT/3 for each CAN channel.
- Automotive AEC-Q100
- CAN FD up to 5 Mbit/s
- Designed for direct use with 3.3 V microcontrollers, including STM32H725
- Standby and wake-up support
- SO8 package, easier to assemble than VSON
- Bus fault protection and excellent automotive EMC performance
Use three TJA1044GT/3 transceivers, one per CAN-FD channel. For improved signal integrity on long or highly branched automotive networks, consider the newer NXP TJA1443 CAN SIC transceiver, but it is larger and requires more support/configuration.
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Block Diagram
Architecture
Text
Vehicle Harness (12 V, GND, CAN1/2/3, optional verified aux) | +--> Automotive input protection | fuse/current limit -> reverse polarity -> load-dump TVS -> EMI filter | | | +--> automotive buck --> 5V_SYS --> 3.3V regulator --> 3V3 | +--> CAN protection/termination --> 3x automotive CAN-FD transceivers | | | +--> STM32H725 FDCAN1/2/3 | USB-C receptacle --> CC1/CC2 Rd, USB ESD, VBUS sense --> STM32H725 USB FS STM32H725 core: - all VDD/VDDA/VREF/VBAT/VCAP support and per-pin decoupling - HSE/LSE only as required by verified panda firmware clock configuration - BOOT0, NRST, SWD, UART/test access - firmware-compatible status LEDs and CAN transceiver controls
Functional Groups and Sourcing Plan
Table
| Block | Reference match | Decision |
|---|---|---|
| Automotive 12 V protection and regulation | None found in Flux reference organization | Datasheet-backed from scratch |
| STM32H725 core | None found | Datasheet-backed from scratch; pin assignment follows public panda red.h and STM32 alternate functions |
| Three CAN-FD channels | None found | Datasheet-backed from scratch using AEC-Q100 3.3 V CAN-FD transceivers |
| USB-C USB 2.0 device | None found | Datasheet-backed from scratch with 5.1 kΩ Rd per CC pin and low-capacitance ESD |
| Harness connector | Public-source verification in progress | Use closest verified family/part only; document mechanical uncertainty |
| Debug / indicators / bring-up | None found | From scratch, firmware definition + MCU datasheet |
Inter-block Nets
- Power:
VBAT_RAW,VBAT_PROT,5V_SYS,3V3,3V3_A,GND - CAN:
FDCAN1_TX/RX,FDCAN2_TX/RX,FDCAN3_TX/RX,CAN1H/L,CAN2H/L,CAN3H/L - USB:
USB_DP,USB_DM,USB_VBUS_RAW,USB_VBUS_SENSE,USB_CC1,USB_CC2 - Control: transceiver standby/enable, selectable termination controls, LEDs,
NRST,SWDIO,SWCLK, debug UART
Scope Boundary
Schematic phase only. PCB outline, exact connector-to-USB-C geometry, placement, routing, and proprietary mechanical details are explicitly deferred.
Architecture
Functional Groups and Sourcing Plan
Inter-block Nets
Scope Boundary
