astra/pd-power-supply

power-trace-audit.md

# Revision 1.1.5 power copper audit

Generated from both compiled circuit JSON files. Widths below are actual copper widths, not only nominal net settings. Dedicated paths connect the USB power junction, fuse, eFuse, shunt and front WAGO connector. The maintained switch only controls EN; it is not in series with the output. Load current does not depend on the controller or sensor escape traces. The 0.3 mm QFN escape centerlines are now 2.15 mm, including 1.20 mm within the power land and 0.75 mm overlapping the 1.5 mm fanout. Only approximately 0.20 mm extends beyond the land before the wide copper begins (less than 0.25 mm at the edges). Previously the 0.3 mm routes were 4.02 and 5.49 mm long. The small fanout pads are copper junctions marked doNotPlace, not fitted parts.

| Path | Width (mm) | Length (mm) | 0.3 mm drill / 0.8 mm pad vias | Estimated resistance (mΩ) |
|---|---:|---:|---:|---:|
| USB_PWR_ESCAPE_A | 0.5 | 2.17 | 0 | 2.14 |
| USB_PWR_ESCAPE_B | 0.5 | 8.70 | 2 | 10.88 |
| LOAD_IN_ESCAPE | 0.3 | 2.15 | 0 | 3.52 |
| LOAD_OUT_ESCAPE | 0.3 | 2.15 | 0 | 3.52 |
| LOAD_IN_FANOUT | 1.5 | 1.95 | 0 | 0.64 |
| LOAD_OUT_FANOUT | 1.5 | 3.32 | 0 | 1.09 |
| PD_RAW_TRUNK | 1.5 | 28.74 | 2 | 11.75 |
| PD_BUS_TRUNK | 1.5 | 55.30 | 1 | 19.28 |
| OUTPUT_BUS_TRUNK | 1.5 | 21.44 | 2 | 9.36 |
| VOUT_WAGO_TRUNK | 1.5 | 20.65 | 1 | 7.93 |

Assumes 35 µm copper, 20 °C copper resistivity 0.0172 Ω·mm²/m and 25 µm via plating through 1.6 mm. The calculation conservatively counts QFN land/trace overlaps twice and uses 0.3 mm for the entire pad escape. The table conservatively treats each USB escape as carrying the full load; both VBUS pad groups are connected to the junction. Estimated positive copper drop at 1 A is **59.2 mV to WAGO**, excluding the 50 mΩ shunt, fuse, eFuse, cable and ground return. Two inner GND pours connect the through-hole output/USB shell grounds; surface ground routes nominally use 1 mm and narrow for local pin escapes.

TI recommends short power paths sized for at least twice the load and substantial copper at the IN/OUT pads: [TPS25947 layout guidance](https://www.ti.com/lit/ds/symlink/tps25947.pdf).

Zero compiled DRC errors in both entries. The audit asserts 1.5 mm dedicated trunks, 0.5 mm USB escapes, 0.3 mm QFN escapes capped at 2.15 mm centerline length and 1.5 mm fanouts, 0.3 mm power-via drills, two inner GND pours, and outward USB/output insertion directions. Width and resistance checks do not establish temperature rise or manufacturing readiness. Verify the stackup, thermal behavior, switching loops, sense pickup and physical switch fit on hardware.