USB-C Smart Sensor Node Design

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Requirements and the initial power budget are now captured in project files. I selected an ESP32-C3 module, SHT40 sensor, TPS25940 eFuse protection, and TPS62840 low-IQ buck regulator sized for Wi-Fi peaks.

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I ran out of execution credits before I could finish wiring and validating the schematic.
Completed so far:
  • Renamed the project to USB-C ESP32 Environmental Sensor Node and updated the description.
  • Created project files:
    • Project Specification
    • Power Budget
  • Selected and added the main schematic components:
    • ESP32-C3-MINI-1-N4 Wi-Fi/BLE MCU module
    • SHT40 temperature/humidity sensor
    • TPS25940 eFuse for reverse/OVP/UVLO/OCP protection
    • TPS62840 750 mA ultra-low-IQ buck regulator
    • USB-C receptacle
    • USB data ESD protection
    • VBUS TVS diode
    • Reset and boot buttons
    • Status LED
    • Buck inductor
  • Consulted datasheets for ESP32-C3, SHT40, TPS25940, USB ESD, and VBUS TVS.
Remaining work:
  • Fetch/verify the TPS62840 datasheet using a corrected URL.
  • Add all required support passives: buck caps/VSET parts, eFuse ILIM/OVP/UVLO/dVdT parts, USB-C CC resistors, I2C pull-ups, MCU/sensor decoupling, EN RC, LED resistor.
  • Wire all nets.
  • Mark unused ESP32/module pins correctly.
  • Run schematic review/ERC and fix violations.
  • Create firmware starter and board bring-up project files.
  • After schematic is clean, ask for confirmation before moving to layout.
Finish schematic wiring
Calculate buck passives
Complete USB-C input
Run design review
Add firmware notes
Sign up to send

Files

Schematic

Layout

3D View

Power Budget
Initial Load Budget

Table

RailLoadSleepTypical activePeak / transient
3.3 VWi-Fi/BLE MCU moduletens of uA in deep sleep80–250 mA~500 mA Wi-Fi TX burst
3.3 VT/RH sensor=750 mA output capability for margin.
  • USB input peak reflected through buck: approximately (3.3 V × 0.51 A) / (5 V × 0.85–0.9) = ~0.37–0.40 A, plus losses.
  • Input protection should tolerate normal operation from 0.5 A USB sources while also being configurable/current-limited for 1.5–3 A capable USB-C supplies.
Thermal Direction
A small LDO at 5 V to 3.3 V could dissipate (5 - 3.3) × 0.25 A = 0.425 W typical during active Wi-Fi, and up to 0.85 W at a 500 mA peak. Use a buck regulator for a cooler consumer product.
Notes
USB-C default current is advertised by Rp on the source and should not be assumed to be 3 A unless detected. This design includes 5.1 kΩ CC pull-downs for sink operation; optional CC current detection can be added if firmware must adapt current draw.

  • Initial Load Budget

  • Sizing Result

  • Thermal Direction

  • Notes