USB-C Temperature and Humidity Sensor Design

flux

I’m blocked from executing changes because the session has no remaining credits, so I could not modify the schematic or add components.
Current project state:
  • Project is still empty: 0 components, 0 nets.
  • No schematic, layout, or validation work has been performed yet.
Recommended design plan for the USB-C Wi-Fi/BLE temperature/humidity node:
  1. Core MCU / radio
    • Use an ultra-low-power Wi-Fi + BLE 5.x MCU/module, likely an ESP32-C6, ESP32-C3, or ESP32-S3 module depending on firmware/security needs.
    • Prefer a certified module with integrated antenna for consumer use to reduce RF certification and layout risk.
    • Include antenna keepout, boot-strapping resistors, EN/reset circuit, UART/programming access, and decoupling per datasheet.
  2. Digital temperature / humidity sensor
    • Use a low-power I²C T/RH sensor such as Sensirion SHT4x/SHT3x-class or TI HDC-series.
    • Place sensor away from MCU, regulator, USB-C connector, and other heat sources.
    • Add I²C pull-ups sized for the selected logic voltage and bus capacitance.
    • Add local decoupling at the sensor.
  3. USB-C 5 V input
    • USB-C receptacle configured as sink with CC1/CC2 pull-down resistors for default 5 V.
    • Design for 0.5–3 A capable sources, while limiting board consumption safely.
    • Add input protection:
      • Reverse-current / ideal-diode or load-switch protection.
      • Over-voltage protection.
      • Under-voltage lockout.
      • Over-current protection / eFuse.
      • ESD protection on USB-C VBUS, CC, and exposed connector lines.
  4. Power architecture
    • Protected USB-C 5 V rail feeds a high-efficiency 3.3 V regulator.
    • Regulator sized from a full power budget: Wi-Fi TX peak current, BLE operation, MCU active/sleep current, sensor current, status LED/debug loads, and margin.
    • Include input/output capacitors exactly per regulator datasheet.
    • Consider a buck regulator rather than LDO for lower heat if Wi-Fi peaks are significant.
  5. Consumer-use details
    • Add ESD protection and robust USB-C input protection.
    • Add status LED with high-value resistor or make it firmware-disableable for low power.
    • Add test pads for 5 V, 3.3 V, GND, UART, EN, BOOT, I²C.
    • Use certified RF module and follow antenna keepout rules.
    • Include mounting holes and enclosure-friendly connector/sensor placement.
  6. Verification still needed
    • Select exact parts using datasheets.
    • Calculate total current budget before selecting USB-C protection, eFuse/load switch, and regulator.
    • Build and wire schematic.
    • Run ERC/review and fix all violations.
    • Simulate/verify power input and regulator behavior where applicable.
    • Only then proceed to PCB placement and routing.
Once credits are available, the next step is to create the schematic from scratch: USB-C protected 5 V input → 3.3 V power rail → Wi-Fi/BLE MCU module → I²C T/RH sensor → programming/test/debug support.
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