USB C Sensor Node
Worked for 1 min 56 sec
Built the schematic for a USB-C powered Wi‑Fi/BLE temperature + humidity sensor node using ESP32‑C3‑MINI‑1‑N4, SHT40, TPS25940 eFuse protection, MP28301 3.3 V buck regulation, USB-C CC pull-downs, USB data ESD, VBUS TVS, reset/boot controls, status LED, and test pads. I also created the key project files: Project Specification, Power Budget and Design Notes, Firmware Starter, Board Bring-Up Plan, and Technical Construction File.
Open items:
- I’m blocked from continuing because your account currently has no available ACUs, so AI tools are unavailable.
- Full check results show expected PCB airwires because layout/routing has not been done yet.
- Several generic passives/testpoints still need final manufacturer part numbers before manufacturing export.
- Layout still needs antenna keepout, SHT40 thermal isolation, USB-C ESD placement, and buck-regulator power-loop placement.
Suggested next steps:
- Refill/enable ACUs, then ask me to finish verification and clean remaining manufacturing metadata.
- Proceed to PCB placement with ESP32 antenna edge keepout and isolated SHT40 placement.
- Route the board, then run DRC/ERC again.
- Lock exact passive/inductor MPNs and generate manufacturing files.
Verify, layout, export
Finish verification
Place components
Route and review
Lock MPNs
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Power Budget and Design Notes — USB-C WiFi T-RH Sensor Node
Architecture Summary
Table
| Stage | Net / Component | Function |
|---|---|---|
| USB-C input | J1, VBUS_RAW | 5 V sink-only input from USB-C. |
| ESD/protection | D1, D2, U3 | VBUS TVS, USB data ESD, TPS25940 eFuse. |
| Protected rail | 5V_PROT | Protected 5 V rail after eFuse. |
| Regulator | U4 MP28301 + L1 | Synchronous buck to 3V3. |
| Load rail | 3V3 | ESP32-C3 module, SHT40, pull-ups, status LED. |
Load Budget
Table
| Rail | Load | Sleep / Idle | Typical Active | Peak / Transient | Notes |
|---|---|---|---|---|---|
| 3V3 | ESP32-C3-MINI-1-N4 | module-dependent, target tens of µA to low mA | 80–160 mA typical Wi-Fi/BLE active | 500 mA radio burst | Use module datasheet and firmware power mode for final value. |
| 3V3 | SHT40 measurement | 0.08 µA typ idle | 0.4–2.2 µA avg at 1 Hz | 0.5 mA measuring, 100 mA max heater | Heater should be firmware-limited. |
| 3V3 | Status LED | 0 mA off | ~1 mA on | ~1 mA | R9 = 1 kΩ. |
| 3V3 | Pull-ups/dividers/PG | ~20–40 µA | ~20–40 µA | same | I2C pull-ups only draw dynamic current during lows. |
Rail Totals
Table
| Rail | Typical Active Estimate | Conservative Peak Estimate |
|---|---|---|
| 3V3 | ~90–170 mA | ~602 mA = 500 mA ESP32 peak + 100 mA SHT40 heater + 1 mA LED + margin |
Regulator Reflection to USB Input
Assume buck efficiency of 90% for the 5 V → 3.3 V conversion.
Table
| Case | 3V3 Load | Estimated 5 V Input Current |
|---|---|---|
| Typical active | 170 mA | (3.3 V × 0.170 A) / (5 V × 0.90) ≈ 125 mA |
| Conservative peak | 602 mA | (3.3 V × 0.602 A) / (5 V × 0.90) ≈ 441 mA |
Protection Sizing
Table
| Item | Selected Value | Rationale |
|---|---|---|
| TPS25940 current limit | R10 = 88.7 kΩ | Datasheet: I(LIM) ≈ 89 / R(kΩ), so ≈1.0 A. Allows startup/radio margin while staying conservative for default-current USB-C. |
| UVLO | R11/R12/R13 ≈ 768k/68.1k/160k | Trip around 4.33 V to avoid brownout-prone operation. |
| OVP | same divider | Trip around 6.16 V for accidental overvoltage above normal USB 5 V. |
| dVdT | C5 = 10 nF | Approx. ramp time tdVdT = 8.3e4 × VIN × C ≈ 4.2 ms at 5 V. |
| VBUS TVS | D1 ESD5341N | 5 V working unidirectional ESD clamp. |
| USB data ESD | D2 USBLC6-2SC6 | Low-capacitance D+/D− ESD protection. |
Regulator Notes
- U4 MP28301GG-P buck output is rated up to 700 mA.
- L1 = 2.2 µH follows the datasheet typical application.
- C8 = 10 µF input, C9 = 22 µF output, C10 = 100 nF HF output cap.
- CTRL1/CTRL2/CTRL3 tied high select 3.3 V.
- CTRL4/CTRL5 tied low disable the unused LDO; OUT2 has C12 = 1 µF only.
Thermal / Accuracy Notes
- Buck regulator was chosen over an LDO because an LDO at 5 V → 3.3 V and 500 mA would dissipate (5−3.3)×0.5 = 0.85 W, heating the board and biasing the temperature sensor.
- Place SHT40 away from the ESP32, regulator, USB connector, LED, and copper pours.
- Sensirion recommends no copper under the SHT40 except pin pads and not soldering the die pad.
USB-C Current Policy
This schematic is a 5 V USB-C sink using CC Rd resistors only. It does not negotiate USB-PD and does not measure Rp current advertisement, so firmware/hardware should remain safe from default-current USB-C sources. The estimated peak input current is below 500 mA for the selected load assumptions.
Open Power Items for Layout / Prototype
- Verify MP28301 inductor exact MPN saturation current and DCR before BOM lock.
- Verify effective capacitance of 10 µF/22 µF MLCCs under DC bias.
- Confirm eFuse startup does not false-trip with final output capacitance and firmware boot load.
- If SHT40 heater must run while Wi-Fi is transmitting continuously, consider a 1 A buck regulator option.
Architecture Summary
Load Budget
Rail Totals
Regulator Reflection to USB Input
Protection Sizing
Regulator Notes
Thermal / Accuracy Notes
USB-C Current Policy
Open Power Items for Layout / Prototype
