ACU Design Status

gyv

gyv

@copilot097

flux

No design changes have been made in this session; the project remains empty with 0 components and 0 nets. Execution is unavailable because the account has no available ACUs—once ACUs are available, the closed-loop DC motor controller schematic and PCB design can proceed.
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Project Specification
Project Overview
Status: Draft schematic capture in progress.
A robust closed-loop brushed DC motor controller for small robotics, driving one bidirectional motor up to 2 A continuous with encoder feedback, MCU control, current monitoring, debug access, status indication, and practical input/output protection.
Intended Use
  • Small mobile robot / actuator controller prototype or production-intent module.
  • External DC motor supply, nominal 12 V, with support for common robotics supply variation.
  • Closed-loop speed and position control implemented in MCU firmware.
What the Device Should Do
  • Drive one brushed DC motor forward/reverse with PWM.
  • Read quadrature encoder A/B and optional index channel.
  • Measure motor current for telemetry and firmware overcurrent protection.
  • Report motor-driver and power-good faults to the MCU.
  • Provide SWD programming/debug, UART/control header, and status LEDs.
Main Features
  • Integrated H-bridge: NXP MC33926PNB, 5 V to 28 V motor supply class, 5 A peak-capable, PWM-compatible, current limit, short-circuit and thermal latch-off protection.
  • MCU: STM32G431CBT6, 170 MHz Cortex-M4F control-oriented MCU with encoder-capable timers, PWM timers, ADC, USART, FDCAN-capable pins, and SWD.
  • Current measurement: INA240A1D PWM-rejection current-sense amplifier across an inline 10 mΩ motor shunt, biased at midscale for bidirectional current.
  • Encoder conditioning: SN74LVC3G17 triple Schmitt buffer, 3.3 V powered with 5.5 V tolerant inputs; per-channel pull-up/filter/series protection and ESD array.
  • Power: 12 V nominal input with fuse/PTC, TVS, ideal-diode reverse-polarity MOSFET stage, and 3.3 V synchronous buck.
System Architecture
Diagram



  
    
  
  
    
  









































12 V DC Input
Input Fuse/PTC
Input TVS
LM74700 + N-MOS Reverse Protection
Protected Motor Supply
MC33926 H-Bridge
Inline 10 mOhm Shunt
Motor Connector
INA240 Current Sense
MCU ADC
LMR33630 3.3 V Buck
3.3 V Logic
STM32G431
Encoder Connector
GPIO ESD
RC + Pull-ups
SN74LVC3G17 Schmitt Buffer
Status LEDs
SWD Header
UART/Control Header
Hardware Subsystems
  • Power input/protection: 2-pin 5 mm terminal block, 3 A+ protection path, SMBJ33CA input TVS, LM74700 ideal-diode controller and 60 V low-RDS(on) N-MOSFET.
  • Logic rail: LMR33630-Q1 buck configured for 3.3 V using datasheet 400 kHz component values.
  • Motor drive: MC33926 with datasheet charge-pump capacitor, bulk VPWR capacitance, status/fault pull-up, slew-rate control, disable control, and motor-output TVS.
  • Current sensing: INA240A1, 10 mΩ shunt, 3.3 V midscale reference, ADC output filter, Kelvin-routed shunt requirement for layout.
  • Encoder input: 6-pin encoder connector carrying 3.3 V, GND, A, B, index, and optional shield/aux; Schmitt buffering protects MCU timing from cable noise.
  • MCU/debug/control: STM32G431 SWD, reset, BOOT0 pull-down, UART/control header, status LEDs.
Interfaces and Connections
  • J1: DC power input, nominal 12 V, expected operating design range 6 V to 24 V within motor-driver/regulator limits.
  • J2: Motor output, bidirectional H-bridge output, 2 A continuous target.
  • J3: Encoder input: 3.3 V, GND, ENC_A, ENC_B, ENC_Z, AUX/SHIELD.
  • J4: SWD programming/debug: 3.3 V reference, SWDIO, SWCLK, NRST, GND, optional SWO.
  • J5: Control UART/GPIO: 3.3 V, GND, UART_TX, UART_RX.
Power and Runtime Expectations
  • External powered; no battery charger or runtime target on this board.
  • Motor current dominates input current. Logic rail load is expected under 250 mA peak.
  • Buck regulator selected instead of LDO to avoid thermal dissipation from 12 V input.
Power Tree and Power Budget

Table

RailLoadTypicalPeak / Design
VMOTOR protectedBrushed DC motorapplication-dependent2 A continuous, driver handles higher transient/current-limit region
VMOTOR protected3.3 V buck reflected input~40 mA at 12 V~100 mA at 12 V for logic peak margin
3.3 VSTM32G43130-100 mA150 mA budget
3.3 VINA240 + logic buffer + LEDs + pull-ups10-30 mA80 mA budget
3.3 V totalLogic rail~150 mA250 mA design budget
Input protection path target: at least 2 A continuous motor current plus logic overhead; fuse/PTC selected near 3 A hold/nominal class and input/motor terminal blocks rated 15 A.
Manufacturing and Assembly Expectations
  • SMD production-ready design with through-hole terminal/header connectors where mechanically useful.
  • Layout must use heavy copper pours/traces for VMOTOR, H-bridge, shunt, and motor output.
  • Thermal pad / exposed pad soldering and copper area are required for the MC33926 and power parts.
  • Kelvin routing required for INA240 shunt inputs.
Firmware-Relevant Hardware Requirements
  • Configure PWM outputs to MC33926 IN1/IN2 or disable-PWM strategy.
  • Use encoder-capable timer channels for quadrature A/B.
  • ADC samples INA240 current output and optional MC33926 FB output.
  • Monitor motor-driver SF fault and buck PG.
  • Fault handling must disable bridge on overcurrent, SF assertion, undervoltage/power-good loss, or firmware watchdog failure.
Physical Design Expectations
  • Keep motor/power loop compact.
  • Keep encoder/control connectors away from H-bridge switching nodes and motor terminals.
  • Place input TVS/fuse/reverse protection near the power connector.
  • Place current shunt inline with motor output and route INA240 Kelvin traces symmetrically.
Important Design Decisions
  • 12 V nominal supply selected as a common robotics voltage; selected ICs support wider operating ranges.
  • Integrated H-bridge chosen over discrete H-bridge for safer fault handling and faster schematic completion.
  • INA240 added for accurate bidirectional PWM current sensing; MC33926 FB kept as an auxiliary coarse current/fault-observability signal.
  • Schmitt-buffered encoder input chosen for cable/noise robustness and 5 V tolerant conditioning.
Assumptions
  • Encoder outputs are open-drain/open-collector or push-pull logic compatible with 3.3 V pull-ups / 5.5 V tolerant buffer inputs.
  • Motor continuous current is 2 A; stall current can exceed this but is handled as a transient by driver current limiting and firmware shutdown.
  • The control host can use 3.3 V UART-level signals.
Change Notes
  • Initial specification created from the user’s request and datasheet-backed component selection.

  • Project Overview

  • Intended Use

  • What the Device Should Do

  • Main Features

  • System Architecture

  • Hardware Subsystems

  • Interfaces and Connections

  • Power and Runtime Expectations

  • Power Tree and Power Budget

  • Manufacturing and Assembly Expectations

  • Firmware-Relevant Hardware Requirements

  • Physical Design Expectations

  • Important Design Decisions

  • Assumptions

  • Change Notes