USB-C WiFi BLE Sensor Node Design
Thought for 9 sec
I’ll pause placement and run the DRC airwire check now, then summarize the remaining unrouted connections by net/component so we can decide what to route next.
Worked for 30 sec
DRC airwire check found 57 unrouted airwires.
Main unrouted groups:
- BUCK_SW / 3.3 V buck area: U2 SW/BST/FB, L1, C4/C5/C6/C7/C8/C10
- 3V3 rail: U2, U3, U4, decoupling caps, I2C pull-ups, boot/strap/fault pull-ups
- VBUS_RAW / VBUS_PROT: J1, D1, U1, C1/C2/C3, U2 VIN/EN
- USB-C / USB data: CC1/CC2, D+/D− through U5 to ESP32-C3
- ESP32 support: EN/reset, BOOT, GPIO2 strap, status LED, eFuse FAULT
- GND stitching/returns: several GND-related airwires remain, including one stitching via connection
Board status:
- Components are already placed on the top layer.
- Board is currently 160 × 100 mm, 4-layer, with very low density (~3.7% component fill), so routing space is generous.
Next step should be routing, but per checkpoint I’ll wait for your approval before running auto-route.
Route buck loop
List airwires
Separate DRC issues
Route USB pair
Add stitching vias
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Power Budget Analysis
Rails
3.3 V Rail Loads
Table
| Load | Sleep | Typical Active | Peak |
|---|---|---|---|
| ESP32-C3-MINI-1-N4 | 5 uA deep sleep | 82-84 mA Wi-Fi RX / 86 mA BLE RX | 350 mA Wi-Fi TX at 20.5 dBm; 340 mA BLE TX at 20 dBm |
| SHT45-AD1B-R2 | 80 nA idle | 0.4-2.2 uA average without heater | 500 uA measurement; up to 100 mA with 200 mW heater |
| I2C pull-ups | 0 A static high | negligible except bus activity | ~0.7 mA per line when low with 4.7 kOhm at 3.3 V |
| Status LED | 0 A off | optional, firmware-controlled | target 1-2 mA |
Design Current Targets
- Normal sensing + periodic Wi-Fi/BLE: design 3.3 V rail for at least 500 mA because Espressif specifies external supply current delivered to VDD33 minimum of 0.5 A.
- Regulator design headroom: AP63203 fixed 3.3 V buck is 2 A capable, leaving headroom for TX bursts, output capacitance, sensor heater use, and startup transients.
- USB input protection: TPS25200 selected for 2.5 A continuous load capability and programmable current limiting. Use RILIM = 56 kOhm for ~1.74 A typical current limit as a conservative default; use 40.2 kOhm for ~2.42 A typical if supporting heavier downstream loads is desired.
Reflected USB Input Current
Assume buck efficiency around 85-90%.
- 3.3 V, 0.5 A output = 1.65 W. USB 5 V input current ~= 1.65 W / (5 V * 0.85) = 0.39 A.
- 3.3 V, 1.0 A output = 3.3 W. USB 5 V input current ~= 3.3 W / (5 V * 0.85) = 0.78 A.
- 3.3 V, 2.0 A regulator max = 6.6 W. USB 5 V input current ~= 6.6 W / (5 V * 0.85) = 1.55 A.
Source Compatibility
- 0.5 A USB-C default source can support normal low-power sensing and radio bursts if firmware duty-cycles Wi-Fi/BLE and limits heater/LED use.
- 1.5 A and 3 A sources provide ample headroom.
- TPS25200 RILIM can be adjusted to enforce the desired product current class.
Datasheet-Grounded Protection Notes
- TPS25200: input operating range 2.5 V to 6.5 V, input withstands 20 V, fixed overvoltage clamp 5.25 V to 5.55 V, OVLO around 7.6 V, UVLO around 2.35 V, and reverse blocking when disabled.
- AP63203: VIN recommended 3.8 V to 32 V and reference design for 3.3 V uses 3.9 uH inductor, 10 uF input capacitor, 2 x 22 uF output capacitors, and 100 nF bootstrap capacitor.
Decision
Use a buck regulator rather than a 500 mA LDO. The ESP32-C3 radio peak current and 0.5 A supply recommendation make a 500 mA LDO marginal, and the buck reduces input current and heat for consumer use.
Rails
3.3 V Rail Loads
Design Current Targets
Reflected USB Input Current
Source Compatibility
Datasheet-Grounded Protection Notes
Decision
