• Drone propulsion ESC board for four independent BLDC motors.
• Prototype/architecture stage; main schematic components are being added first, followed by supporting passives, MOSFET power stages, protection, sensing, and firmware documentation.
• Motor current sizing basis for initial MOSFET and copper sizing: 20 A continuous, 36 A max, and 52 A peak spike per motor. Motor KV, pole count, board size, cooling, firmware update interface, and some mechanical constraints remain open.

• Control four Hall-sensored BLDC motors from one PCB.
• Use one DRV8308 per motor channel.
• Use each DRV8308 for Hall-based commutation and motor-speed control.
• Use STM32G474 MCUs to configure DRV8308 registers over SPI, command speed/direction, monitor faults, coordinate channels, and communicate with the flight controller.
• Provide external motor phase outputs and Hall sensor connections for each motor.

• Input: 22 V nominal battery bus.
• Compute: 2 × STM32G474CBT6, 3.3 V logic.
• Motor control: 4 × DRV8308, each driving 6 external N-channel MOSFETs for one 3-phase BLDC motor.
• Feedback: 3 Hall sensor channels per motor connected to the corresponding DRV8308.
• Telemetry: temperature-only telemetry exposed through the flight-controller interface.
• No onboard datalink transmitter or receiver on the drone.
• Debug/programming: SWD connector per MCU recommended.
• ESC ↔ flight-controller interface: SPI, selected for fast low-cost communication in a stacked-board architecture.
• Inter-MCU link: SPI preferred unless pin routing or firmware partitioning favors FDCAN internally.

Diagram

• 22 V nominal battery input; exact chemistry and voltage range TBD.
• Needs reverse-polarity protection, TVS surge protection, fuse/current protection, low-ESR bulk capacitance, and per-inverter ceramic decoupling.
• Must be sized from motor stall/peak current, not nominal voltage alone.

• STM32G474CBT6 is suitable for control/supervisory firmware: Cortex-M4F, high-resolution timers, advanced motor timers, ADCs, op-amps, comparators, CORDIC/FMATH accelerators, SPI/UART/FDCAN.
• In this DRV8308 architecture, the MCU does not directly generate six PWM gate signals per motor; it commands/configures DRV8308 channels.
• Two motors per MCU is reasonable for supervisory control, SPI programming, command generation, fault monitoring, and telemetry.

• Selected motor: Skystars Koko 2207.5 / 2275 1950KV, intended for 6S LiPo and 5-inch propellers.
• Motor source: https://www.rotorama.com/product/skystars-koko-2207-5-1950kv
• Key motor specs: 1950KV, 2207.5 stator, 12N14P, 5 mm shaft, 16×16 mm M3 mounting, 32 g, 20 AWG 150 mm leads.
• Current basis: published secondary listing indicates 36 A max for 180 s and 1000 W max continuous power for 180 s; design continues to assume 20 A continuous, 36 A max, and 52 A transient spike per motor.
• Use 4 × DRV8308, one per BLDC motor.
• Each DRV8308 drives 6 external N-channel MOSFETs.
• Initial MOSFET selection for each inverter switch: Vishay SiR680ADP-T1-RE3, 80 V N-channel PowerPAK SO-8, RDS(on) 2.88 mΩ max at VGS = 10 V, Flux UID 7dd3f499-5e82-4684-9088-702c9a94720b.
• Each motor channel needs: DRV8308, 6 MOSFETs, bootstrap/charge-pump support components, current-limit sense resistor path, motor phase connector, Hall connector, bulk/ceramic bus capacitance, and fault/speed/control signals to MCU.
• DRV8308 supports Hall-based commutation and optional closed-loop speed control; this is not true MCU-run FOC.

• Battery input connector: current rating TBD.
• Four motor phase connectors: U/V/W per motor.
• Four Hall sensor connectors: Hall U/V/W plus Hall supply and ground per motor.
• Flight-controller command/telemetry interface: SPI. It must carry motor commands into the ESC and temperature-only telemetry back to the flight controller.
• SPI is selected because the boards are expected to be stacked or connected over a short board-to-board interconnect, making external transceivers unnecessary.
• Board-to-board connector: Samtec TFC/SFC and TFM/SFM Tiger Eye 30-contact options were checked for the stacked ESC/flight-controller SPI interface, but the matching header configurations are marked Existing Customers Only by Samtec. Do not commit those footprints unless procurement confirms access.
• Current implementable fallback in Flux: Samtec ERM8/ERF8 0.80 mm Edge Rate mezzanine family, 60 contacts, 10 mm stack height, SMT footprints available in Flux. This is more pins/cost than the original 30-contact target but gives ample spare pins and rugged board-to-board mechanics.
• No datalink radio/transmitter/receiver is to be included on the drone electronics.
• Inter-MCU communication: SPI preferred for low cost and speed; define master/slave ownership during firmware architecture.
• Programming/debug: SWD + reset per STM32.

• Battery system: 6S LiPo, 22.2 V nominal, approximately 25.2 V fully charged and approximately 18.0 V at conservative discharge cutoff.
• User prefers the battery/power-management function on a separate board, but would like it incorporated onto the flight controller if space and thermal/current routing allow.
• Logic rails: 3.3 V for STM32 and logic.
• DRV8308 motor supply: 8.5–32 V operating range, compatible with nominal 22 V if battery maximum remains below 32 V.
• Hall supply: DRV8308 includes 5 V regulator output for Hall sensors, limited current per datasheet; verify total Hall sensor current.
• Motor bus: 22 V nominal, final min/max TBD.

• Downstream boards to be powered, with voltage/current requirements for each board.
• Per-motor current basis: 20 A continuous, 36 A max, 52 A peak spike. Spike duration and repetition rate still TBD.
• Motor KV, pole count, maximum RPM, and Hall sensor voltage/current.
• Cooling assumptions: airflow, copper area, enclosure constraints.

• Add a 6S power-management board function that accepts the battery pack and distributes protected power to the ESC, flight controller, and E/O camera.
• Provide surge protection for each powered board output, not just one shared input TVS.
• Recommended protection per high-current output: appropriately rated fuse/eFuse or current limiter, TVS diode to power ground, reverse-current/reverse-polarity strategy as needed, local bulk capacitance, and connector sized from the target load current.
• Telemetry requirement: temperature telemetry only. Do not add battery/current telemetry as a user-facing telemetry requirement unless later requested.
• Recommended temperature sensing locations: ESC power stage/MOSFET area, DRV8308/driver area, regulator/power-management hot spot, flight-controller board hot spot, and E/O camera power output/regulator hot spot if present.
• User-requested thermal sensing: add one temperature sensor near each MOSFET bridge, plus sensors at power-management hot spots including battery input/protection and main regulator/current-distribution area. Temperature data is reported through the SPI flight-controller interface.
• Integration decision: keep the power-management function separate unless the flight-controller PCB has enough area for high-current copper, thermal relief, connector clearance, and noise isolation from IMU/radio/MCU circuitry. If incorporated onto the flight controller, separate the high-current battery path physically from sensors and low-noise analog sections.

• High-current ESC layout requires at least 4-layer PCB with heavy copper and very wide pours. Initial recommendation: 2 oz copper minimum, 3–4 oz preferred for the ESC power board if 80 A continuous is realistic.
• 80 A continuous board-current sizing cannot be handled as a normal trace. Use broad top/bottom VBAT and PGND pours, dense via stitching, short high-current loops, and possibly solder-thickened exposed copper or busbar-style reinforcement.
• IPC-2221 external-copper estimate for 80 A continuous: with 4 oz copper, ~20.8 mm width for 20°C rise or ~16.3 mm for 30°C rise; with 3 oz copper, ~27.7 mm for 20°C rise or ~21.7 mm for 30°C rise.
• Thermal design and current-limit sense layout are critical.
• DRV8308 VQFN and high-current MOSFET layout are not beginner-friendly for hand assembly.

• Per DRV8308: SPI configuration path or programmed NVM strategy, speed command, direction, enable, fault output, lock/status, optional FG/speed feedback.
• Per motor: Hall U/V/W inputs to DRV8308.
• Per MCU: SWD, boot/reset, debug UART, watchdog/failsafe behavior.
• Firmware architecture must define master/slave behavior or partition two motors per MCU.
• Flight-controller interface firmware must report temperature-only telemetry and must not depend on an onboard datalink radio.
• SPI protocol must include command framing, temperature telemetry frames, fault/status bits, CRC or checksum, and timeout/failsafe behavior.

• Board partition decision locked: use two separate PCBs — one ESC PCB and one power-management PCB.
• Each PCB must independently fit within a maximum footprint of approximately 60 mm width × 200 mm length.
• Treat 60 mm as the controlling dimension for high-current bus layout, connector placement, mounting holes, airflow, and heatsinking.
• High-current power paths should run lengthwise where possible so 40–50 mm equivalent copper/busbar width can be preserved without consuming the whole board width.
• Mounting holes, connector placement, airflow, and heatsinking details are still TBD within this footprint.
• Keep motor phase loops compact and separate noisy power stages from MCU analog references.
• Place each DRV8308 close to its MOSFET bridge and current-sense path.
• Verified but not recommended for new design unless procurement confirms access: Samtec TFC-115-22-F-D-A + SFC-115-T2-F-D-A, 30 contacts, 1.27 mm pitch, SMT, 10.00 mm mated stack height per SFC/TFC catalog; Samtec product pages mark the parts Existing Customers Only.
• Verified but not recommended for new design unless procurement confirms access: Samtec TFM-115-22-L-D-A + SFM-115-02-L-D-A, 30 contacts, 1.27 mm pitch, SMT, rugged Tiger Eye family; header availability is restricted/Existing Customers Only.
• Selected implementable footprint direction: Samtec ERM8-030-05.0-S-DV-K-TR header + ERF8-030-05.0-S-DV-L-K-TR socket, 60 contacts, 0.80 mm pitch, SMT, 10.00 mm mated height with -05.0/-05.0 lead styles. Flux library parts found: ERM8 UID 3747610b-dcb6-4a0d-8325-7892b232f832 and ERF8 UID 4df3cff0-3881-4448-a4fa-8b5cf137c179.
• Caveat: Samtec product pages for ERM8/ERF8 configurations also show Existing Customers Only notices, so procurement must confirm orderability before layout release. If procurement cannot source them, create/import an available Molex SlimStack 10 mm pair or another open-order Samtec alternate before PCB layout.
• Rationale: ERM8/ERF8 has verified 10 mm stack-height documentation, rugged/high-speed board-to-board construction, available Flux footprints, and 60 contacts for generous spare pins. Avoid using the connector as the only mechanical support; add 10 mm standoffs near the connector.
• Reserve enough pins for SPI SCLK/MOSI/MISO/CS, interrupt/data-ready, reset or enable, shared ground returns, 3.3 V reference/logic supply if needed, temperature-alert lines if used, and spare GPIOs. With the 60-contact ERM8/ERF8 fallback, target at least 20 spare/ground pins after assigning required SPI, control, power-reference, and ground pins.
• Keep SPI traces short, length-matched only if clock speed requires it, and interleave/adjacent ground pins where possible to improve signal integrity across the stack.

• Do not carry motor/battery current through the mezzanine connector.
• Treat 3V3_IO_REF as a logic-level reference or very-low-current sense rail only; ESC MCU power remains on the power-management 3V3_A rail.
• Keep SPI pins adjacent to ground returns and route SCK/MOSI/MISO as short controlled-return traces across the stack.
• Firmware must implement CRC/checksum, command timeout, hardware arm gating, and safe motor shutdown if SPI heartbeat is lost.

• Architecture locked by user: choose cheaper 4 × DRV8308 sensored BLDC approach instead of true FOC.
• One DRV8308 controls exactly one BLDC motor.
• Back-EMF sensing is not the primary control method in this architecture; Hall sensors drive commutation.
• Battery system locked by user: 6S 22.2 V nominal pack.
• New system requirement: design a power-management/distribution board with surge protection for every downstream board it powers; evaluate incorporating this function onto the flight controller if board space and noise/thermal constraints permit.
• Downstream powered boards locked by user: ESC, flight controller, and E/O camera for autonomous flying.
• Telemetry decision locked by user: temperature telemetry only, accessed through the flight-controller interface; no drone-mounted datalink transmitter or receiver.
• Interface decision locked by user: SPI between stacked ESC and flight-controller boards for fastest communication at low manufacturing cost.
• Connector decision locked by user: low-cost board-to-board mezzanine connector for the SPI stack.
• Stack-height decision locked by user: 10 mm spacing between ESC and flight-controller PCBs.
• Connector verification result: original Samtec low-cost Tiger Eye TFC/SFC 30-contact option meets 10 mm stack height but is restricted by Samtec as Existing Customers Only. Use ERM8/ERF8 Flux footprints as the current implementable option, subject to procurement confirmation.
• Power-stage sizing note created: see Power Stage Sizing Notes for MOSFET selection, copper-width calculations, stackup assumptions, and temperature-sensor placement.
• Board partition locked by user: separate ESC PCB and power-management PCB, each with its own 60 mm × 200 mm maximum footprint.
• SPI mezzanine pinout defined for the 60-contact ERM8/ERF8-style connector: shared SPI bus, independent U1/U2 CS/INT/FAULT/RESET/READY lines, heartbeat/sync/arming lines, 18 ground pins, and 18 spare/reserved pins.

• 22 V battery means nominal voltage; actual min/max not yet confirmed.
• Four motors are independent propulsion channels.
• User wants one PCB, not four separate ESC modules.
• DRV8308 open-loop/closed-loop speed control is acceptable versus true torque FOC.

1. What are the remaining motor specs: voltage, KV, pole count, 36 A max duration, 52 A spike duration/repetition rate, and Hall sensor current?
2. What current and voltage rails are required by the flight controller and E/O camera?
3. Confirm connector procurement access, then create the SPI stack pinout using the selected ERM8/ERF8 60-contact footprint or an approved open-order alternate.
4. Within the 60 mm × 200 mm maximum footprint, what exact board split, mounting-hole pattern, and airflow/cooling assumptions should be used?
5. Should DRV8308 configuration be done by SPI at every boot, external EEPROM, or OTP programming?
6. What temperature sensor topology should be used: analog NTC thermistors to STM32 ADCs, digital I2C/SPI temperature sensors, or both?

• User selected the cheaper DRV8308 approach.
• Architecture updated to 4 × DRV8308, one per motor, with Hall-sensor feedback.
• User specified a separate 6S 22.2 V battery/power-management board concept, with preference to integrate onto the flight controller if feasible.
• User specified powered downstream boards: ESC, flight controller, and E/O camera.
• User specified temperature-only telemetry through the flight controller interface and no onboard datalink transmitter/receiver.
• User selected SPI for the ESC ↔ flight-controller interface because the boards may be stacked.
• User requested a low-cost board-to-board mezzanine connector for the SPI stack.
• User specified 10 mm stack height between ESC and flight-controller boards.
• Samtec connector drawings were checked. TFC/SFC 30-contact option gives 10.00 mm stack height but is Existing Customers Only. ERM8/ERF8 60-contact 10 mm option has Flux footprints and is the current implementable fallback, but procurement access still needs confirmation.
• User specified motor current basis for initial sizing: 20 A continuous per motor, 36 A max per motor, and 52 A peak current spike per motor. Four-motor board-level cases are 80 A continuous, 144 A max, and 208 A simultaneous spike.
• Initial MOSFET selected for sizing: Vishay SiR680ADP-T1-RE3, 80 V PowerPAK SO-8.
• User requested temperature sensors near each MOSFET bridge and power-management hot spots.
• Initial copper/stackup recommendation added: 4-layer minimum, 2 oz minimum copper, 3–4 oz preferred for the ESC power board, with wide pours/busbar-style distribution for 80 A continuous.
• User specified that all PCB boards must fit within an approximate maximum footprint of 60 mm width × 200 mm length.
• User confirmed separate ESC and power-management PCBs, each independently limited to approximately 60 mm × 200 mm maximum footprint.