seveibar/nema17-rp2040-stepper-controller

REVISION.txt

COMPACT USB REV D — 42 x 42 mm NEMA 17 controller
Engineering prototype; not fabrication-released.

Supersedes USB-ISO B. Both USB ports now share motor ground.
Removed ISOUSB111, NXE1S0505MC, EL357 optocoupler and isolation keepout.
Four 3.3 mm mounting holes retain 31 x 31 mm spacing. All populated components
are on top, with four copper layers. Encoder and its support parts are DNP.
Standoffs must clear motor hardware and exposed PCB copper. USB connector courtyards
remain inside the 42 mm board; attached cable plugs extend outwards.

DATA-only: laptop 5 V -> D_LAPTOP_OR -> LMR16006 buck -> 3.3 V logic.
PWR+DATA-only: CH224K negotiates PD; data passes through CH9442 guard and mux.
Both: DTC114E host detector selects DATA; PWR supplies motor/logic.
The PWR and DATA VBUS rails are not tied together. D_PWR_OR and D_LAPTOP_OR
provide reverse blocking; D_MOTOR_BLOCK remains in the motor input path.
This protection is not galvanic isolation or a guarantee against all faults.

Two CH9442Q chips remain: selector common XA/XB faces MCU; separate guard XA/XB
faces PWR connector (the pins specified for 28 V OVP). PWR low-voltage ESD clamp
stays behind the guard. CH224K D+/D- remain locally shorted for PD-only mode.
No added USB firmware proxy is required. A charger is not a USB host, and a
normal 5 V laptop output does not provide suitable DRV8825 motor voltage.

Required physical qualification: current/inrush/suspend budgets; programming
and enumeration; powered/unpowered port handover; USB full-speed signal quality;
PD transitions, reverse leakage/backfeed, ESD and motor transients; thermal and
mechanical clearance, component orientation and footprint verification.
No deliberately timed USB disconnect interval is implemented.

Reproduce: bun install; bun run verify
Viewer: bunx tsci build index.circuit.tsx --site --disable-parts-engine

Sources:
https://www.wch.cn/products/CH9442.html
https://www.ti.com/lit/ds/symlink/lmr16006.pdf

Compact alarm: MLT-5020 (C94598), 5.2 mm body, 3 V externally driven magnetic buzzer. Use approximately 4 kHz PWM; do not leave the coil continuously driven. Existing MOSFET and flyback diode are retained.