Board P — USB-PD Front End

The USB-PD 15V/3A sink front end for this lamp — adapted from the zudo-pd project's reusable Board A core (STUSB4500 + USB-C receptacle + load switch + NVM/debug pads), audited against primary datasheets rather than copied verbatim.

Board P is this lamp's dedicated USB-PD processing board. It negotiates a 15 V/3 A USB-PD contract from a USB-C charger, load-switches it, and hands a clean switched 15 V rail (plus GND and two optional status flags) to whatever board consumes power downstream — the LED power stage and/or control board being researched in parallel as separate doc sections. The exact board split is locked by the prototype-architecture decision, not by this page.

The circuit below is adapted from the zudo-pd project's "Board A" — a small, reusable USB-PD 15 V sink module the zudo-pd project split out specifically so other projects could reuse it. This page is an audit, not a copy-paste: every LCSC part number was re-verified against the local JLCPCB parts database, and every rating claim was re-checked against the actual manufacturer datasheet rather than trusted from zudo-pd's prose. One part failed that check — see Worst-Case Ratings Matrix for the USB-C receptacle swap this audit made.

Purpose

• Proven front-end topology. zudo-pd's single-board design failed USB-PD negotiation across four separate PCBA orders (v1–v4) before the front end was diagnosed, fixed on paper, and split into its own board. Board P inherits that post-fix topology directly, rather than re-deriving it from scratch.

• Generic, reusable "switched 15 V sink" module. Nothing in this circuit is lamp-specific — it negotiates 15 V over USB-PD, switches it, and exposes GND plus two generic status flags. Any downstream board that just needs a switched 15 V rail can consume it.

• NVM-programmable. The same board carries I2C pogo pads for writing the STUSB4500's PDO configuration — see Lessons Carried From zudo-pd for the factory-default 20 V trap this NVM step exists to close.

Block diagram

Net-connectivity table

Per the zudo-pd project's net-table + Mermaid convention (a "never ASCII-art schematics" documentation rule — connectivity is recorded as a table derived from netlist data, illustrated at block level by Mermaid). This table describes the target circuit for Board P's own future schematic; it is not yet exported from a KiCad netlist because that schematic does not exist yet.

Component list, LCSC parts, and rough cost

All LCSC numbers below were independently re-verified via the local JLCPCB parts database (dated 2026-07-25) — not copied from zudo-pd's BOM page, which that project's own docs flag as having drifted. https://jlcpcb.com/partdetail/C{number} links are included for each. See Worst-Case Ratings Matrix for the per-part rating evidence and the one part this audit swapped out.

DNP (footprint only, not populated):

Downstream interface

Board P exposes exactly what a "switched 15 V sink module" needs to hand off: switched 15 V (paired, 2 pins), GND (paired, 2 pins), and two optional open-drain status flags — ATT (cable attached) and PDOK (live 15 V PD contract). This mirrors the interface contract zudo-pd's Board A uses toward its own downstream board, reusing the same connector choice (JST B6B-XH-A(LF)(SN), 6-pin, 2.5 mm pitch, 3 A/contact) for the same reasons: polarized/shrouded housing, genuine-JST stock at JLCPCB, and through-hole anchoring appropriate for a power connector.

Current-rating math (same method zudo-pd used for its A↔B interface): worst case is the PD contract cap of 3.0 A at 15 V. The XH connector is rated 3.0 A/contact; at an 80% continuous derate that is 2.4 A/contact. Two contacts per power rail give 4.8 A derated capacity against a 3.0 A load — each contact carries 1.5 A, 50% of nameplate, for a 1.6× derated margin (2.0× nameplate). GND uses the identical two-contact math.

Reuse guidance

• Minimum wiring: connect the two VBUS_OUT pins and two GND pins to the consuming circuit. ATT/PDOK may be left unconnected — Board P negotiates and switches power autonomously.

• NVM reconfiguration: the negotiated voltage/current live in the STUSB4500's NVM, not in the schematic — see Lessons Carried From zudo-pd for the programming procedure and its pitfalls.

• Electrical limits to respect downstream: anything wired to VBUS_OUT must tolerate the D5 (SMAJ20A) clamp ceiling during a fault event, not just the nominal 15 V — see Worst-Case Ratings Matrix for the exact numbers and which parts have residual (accepted, transient-only) margin gaps against that ceiling.

References

• The zudo-pd project's Board A design (STUSB4500-based reusable USB-PD 15 V sink core) — the direct source of this circuit, credited throughout this page.

• Worst-Case Ratings Matrix — per-part datasheet-sourced rating verification, including the USB-C receptacle swap.

• Charger Compatibility — why the front end uses an auto-negotiating certified controller instead of a resistor-strapped one.

• Lessons Carried From zudo-pd — design rules, the NVM factory-default trap, JLCPCB CPL gotchas, and the standalone bring-up sequence.