STUSB4500 NVM Programming Setup

The STUSB4500 requires NVM (non-volatile memory) programming to configure its USB-PD negotiation behavior. Factory defaults will negotiate 20V (not 15V), which would damage downstream circuits. This page documents the hardware setup, required NVM values, and schematic changes needed.

Why NVM Programming Is Required

The STUSB4500QTR ships from the factory with these default PDO profiles:

Problems with Factory Defaults

1. Wrong voltage: PDO3 (20V) has highest priority. With multi-voltage chargers (5V/9V/15V/20V), the IC negotiates 20V instead of 15V. This feeds 20V into DC-DC converters designed for 15V input.

2. Insufficient current: Even when 15V is negotiated (charger lacks 20V), only 1.5A is requested. The design needs 3A.

3. No power sequencing: POWER_ONLY_ABOVE_5V defaults to disabled, so VBUS_EN_SNK enables at 5V before PD negotiation completes. This exposes downstream circuits to voltage transitions.

Target NVM Configuration

The safest configuration eliminates PDO3 entirely so 20V is never an option, regardless of how the STUSB4500 prioritizes PDOs internally:

Additional settings:

• SNK_PDO_NUMB = 2 (only PDO1 + PDO2; PDO3 never advertised → 20V never requested)

• POWER_ONLY_ABOVE_5V = enabled (VBUS_EN_SNK only activates after 15V negotiation succeeds)

Hardware Required

Programming Tool: Pogo Pin Clip (4P, 2.54mm)

A spring-loaded pogo pin clip clamps onto the PCB edge and contacts bare copper pads for temporary I2C connection. No soldered header needed.

Clip mechanical specs:

• AliExpress item: 1005006108783889 (equivalent to Adafruit 5433 / The Pi Hut variant)

• Max landing depth: 25 mm from board edge — the clip body cannot reach further inward

• Recommended landing: 2–3 mm inward from the board edge — gives the clip body a lip to grip and centers the pogo tips on the pad

• Minimum pad-to-edge clearance: 0.3 mm for JLCPCB manufacturing (0.5 mm is safer to avoid routing issues)

Option A: NUCLEO-F072RB + STSW-STUSB002 GUI (Recommended)

Only one board is needed. The STEVAL-ISC005V1 eval board is not required since we program the STUSB4500 on our own PCB.

The Nucleo board acts as a USB-to-I2C bridge when flashed with the included .bin firmware.

Connection:

Windows PC ─── USB ───→ NUCLEO-F072RB ─── pogo clip ───→ zudo-pd board edge pads
                        D15 (PB8) = SCL ────────────────→ J2 pad 1 (SCL)
                        D14 (PB9) = SDA ────────────────→ J2 pad 2 (SDA)
                        GND ────────────────────────────→ J2 pad 3 (GND)
                        (unused) ───────────────────────→ J2 pad 4 (NC)

The pogo clip's dupont wires connect to the Nucleo's D14, D15, and GND pins. The clip clamps onto the zudo-pd board edge where J2 pads are located.

The Nucleo I2C operates at 3.3V, compatible with STUSB4500's VREG_2V7 (2.7V) via open-drain I2C bus. No level shifter needed.

Option B: Arduino / MCU via I2C (Alternative)

If you already have a 3.3V Arduino or similar MCU board, the SparkFun STUSB4500 Arduino Library supports full NVM programming via write(). No Windows GUI needed.

Requirements:

• Arduino or MCU board with 3.3V I2C (not 5V - would need level shifter)

• SparkFun library installed

• Connect SCL, SDA, GND to zudo-pd J2 pads via pogo clip

Schematic Changes for I2C Programming Pads

The v1 schematic has SCL (pin 7) and SDA (pin 8) as NC (not connected). These must be connected to edge pads with pull-up resistors for NVM programming.

New Components

KiCad Symbol and Footprint

Pad placement on PCB:

The 4 SMD pads sit in a single row. J2 must be placed at the PCB edge so the pogo clip can grip the board — see the PogoPad footprint design subsection below for the concrete pad/layer/silkscreen spec.

                    PCB edge
───────────────────────┐
                       │
  ○ SCL  (pad 1)      │  ← 2.54mm pitch
  ○ SDA  (pad 2)      │     bare copper pads
  ○ GND  (pad 3)      │     within ~10mm of edge
  ○ NC   (pad 4)      │
                       │
───────────────────────┘

PogoPad footprint design

The footprint PogoPad_1x04_P2.54mm records the concrete numbers used in the actual KiCad file:

Why no solder paste (F.Paste)? Pogo pins contact bare copper directly — no solder joint is formed. Including F.Paste would deposit solder paste on these pads during SMT manufacturing, which would harden into a rough surface that prevents reliable pogo tip contact. JLCPCB also rejects paste on edge pads. Omitting F.Paste keeps the copper surface clean and exposed.

Silkscreen markings:

• Pin labels: SCL, SDA, GND, NC (one per pad)

• An edge-side line running parallel to the pad row, indicating the board edge

• A <-- EDGE text marker placed outside the board outline (for placement orientation only — this gets cut off during PCB fabrication, which is intentional)

File locations in this repo:

• footprints/kicad/PogoPad_1x04_P2.54mm.kicad_mod (master copy)

• footprints/kicad/zudo-power.pretty/PogoPad_1x04_P2.54mm.kicad_mod (KiCad library path)

Both locations must exist and stay in sync. See footprints/CLAUDE.md for the dual-location rule and the workflow for keeping them in sync.

Circuit

                    VREG_2V7 (pin 23, 2.7V)
                         │
                    ┌────┴────┐
                    │         │
                R15 (4.7kΩ) R16 (4.7kΩ)
                    │         │
SCL (pin 7) ────────┤         │
                    │         │
SDA (pin 8) ────────┼─────────┤
                    │         │
              J2 pad 1     J2 pad 2     J2 pad 3    J2 pad 4
                (SCL)       (SDA)        (GND)       (NC)
                    │         │            │            │
              ┌─────┴─────────┴────────────┴────────────┴──┐
              │        J2 (Pogo Pads, 1x4, 2.54mm)         │
              │        Bare copper pads at board edge       │
              └────────────────────────────────────────────┘

Pull-ups connect to VREG_2V7 (2.7V) since this is the I2C bus voltage for the STUSB4500. The Nucleo's 3.3V I2C is compatible with 2.7V open-drain signaling.

Connection List

• STUSB4500 SCL (pin 7) → R15 (4.7kohm) → VREG_2V7

• STUSB4500 SCL (pin 7) → J2 pad 1

• STUSB4500 SDA (pin 8) → R16 (4.7kohm) → VREG_2V7

• STUSB4500 SDA (pin 8) → J2 pad 2

• J2 pad 3 → GND

• J2 pad 4 → NC (not connected)

Programming Procedure

Step 1: Flash the Nucleo Firmware

1. Download STSW-STUSB002 from ST website

2. Extract the archive — you'll find two .bin files:

• Nucleo_F072RB_STUSB_HID_NVM_config_*.bin (HID variant)

• Nucleo_F072RB_STUSB_UART_NVM_config_*.bin (UART variant)

3. Use the UART variant. Reason explained in the callout below.

4. Connect NUCLEO-F072RB to Windows PC via USB (CN1, the ST-Link USB Mini-B)

5. The Nucleo appears as a USB mass storage device labeled NODE_F072RB

6. Drag the UART .bin file onto the Nucleo drive

7. The LD1 LED blinks rapidly during flashing, then settles. The drive will disappear/remount.

8. Unplug and replug USB — the Nucleo needs to re-enumerate with the new firmware

9. Verify in Windows Device Manager: Ports (COM & LPT) should show "STMicroelectronics STLink Virtual COM Port (COMx)". If no COM port appears, install the ST-Link VCP driver.

Sources:

• STSW-STUSB002 quick start guide (PDF) — explicit UART vs HID guidance

• NUCLEO-F072RB schematic (MB1136-C03) — confirms CN1 is ST-Link only

Step 2: Connect to zudo-pd Board

1. Use a low-power USB-C charger for the programming session — see warning below

2. Plug the charger into the zudo-pd USB-C connector (to power the STUSB4500 via VDD)

3. Connect the pogo clip's dupont wires to the Nucleo's Arduino-compatible CN5 header:

• Nucleo D15 (SCL, labeled on board silkscreen) → pogo clip wire for pad 1

• Nucleo D14 (SDA) → pogo clip wire for pad 2

• Nucleo GND (any GND pin) → pogo clip wire for pad 3

• Pogo pad 4 unused

4. Clamp the pogo clip onto the zudo-pd board edge, aligning the pogo pins with J2 pads

5. The STUSB4500 should be detected at I2C address 0x28

Step 2.5: If the GUI Still Says "STUSB4500 not Detected"

Before debugging the Nucleo or STSW-STUSB002, first prove the zudo-pd board is actually powered on the STUSB4500 side.

Do not use TP1 / TP3 / TP4 / TP5 for this check. TP1 is downstream of the Q1 load switch, and TP3-TP5 are downstream converter rails. These can all read 0 V during NVM programming, especially before a valid PD contract enables VBUS_EN_SNK.

Use the J3 debug pogo block instead:

Decision tree:

If J3 pad 4 is 0 V with a USB-C-to-USB-C charger, try a known-good USB-A-to-USB-C 5 V source. USB-A-to-C supplies 5 V directly through the cable, which separates "board cannot request VBUS over CC" from "VBUS trace or chip supply is physically broken."

[OK] STUSB4500 Detected [COM3] ST-ii0244, at address 0x28 (I2C bus 1)

Step 3: Program NVM

1. With chip detected (status bar shows [OK] STUSB4500 Detected), click "Read device NVM" to load actual chip values into the GUI

2. The "SNK Parameters" tab will populate with the factory defaults — confirm they match the expected defaults (PDO1: 5V/1.5A, PDO2: 15V/1.5A, PDO3: 20V/1.0A)

3. Configure target settings:

4. Verify "Verify after write" checkbox at top-right is checked (default)

5. Click "Write device NVM"

6. Wait for the write to complete and verification to succeed

Step 4: Verify

1. Click "Read device NVM" again to confirm the new values stuck (especially POWER_ONLY_ABOVE_5V — it sometimes doesn't save on the first write)

2. Remove the pogo clip from the board

3. Reconnect a real USB-C PD charger that supports 15V

4. Measure VBUS_OUT with a multimeter — should read 15V (or 5V if charger doesn't support 15V — fallback behavior)

5. Verify VBUS_EN_SNK behavior (should stay LOW at 5V, go HIGH only after 15V negotiation completes)

Verifying via the GUI's Dashboard tab

The "Dashboard" tab shows real-time CC state — useful for diagnosis. With charger plugged in and pogo clip still attached:

• CC Connection section should show "Sink attached" or similar (NOT "No device attached")

• CC Operation should show the negotiated PD contract (voltage, current)

• Monitoring shows live VBUS voltage and current

If Dashboard says "No device attached" while a PD charger is plugged in, the chip's CC pins are not seeing a valid source termination — this is a hardware-level issue, not a NVM issue. See PCBA v2 Debug Report for the CC1DB internal short failure mode we encountered.

NVM Write Cycle Limit

The STUSB4500 NVM is rated for approximately 1,000 write cycles. Configure once during production. Do not write NVM repeatedly in normal operation.

Common Pitfalls (from actual programming sessions)

Schematic Fix Checklist

• [x] Remove no-connect markers from SCL (pin 7) and SDA (pin 8)

• [x] Add R15 (4.7kohm, 0603) from SCL to VREG_2V7

• [x] Add R16 (4.7kohm, 0603) from SDA to VREG_2V7

• [x] Add J2 symbol (Connector_Generic:Conn_01x04) connected to SCL, SDA, GND, NC

• [x] Create custom footprint PogoPad_1x04_P2.54mm in zudo-pd library

• [x] Assign footprint to J2

• [x] Place J2 pads at board edge in PCB layout

• [x] Run DRC

References

• STSW-STUSB002 Data Brief (PDF) - GUI tool documentation

• STSW-STUSB002 Quick Start Guide (PDF) - HID vs UART .bin selection guidance

• STSW-STUSB002 Download - Software download page

• STSW-LINK009 - ST-Link VCP Driver - Required if COM port doesn't appear in Device Manager

• NUCLEO-F072RB Schematic (MB1136-C03 PDF) - Confirms CN1 USB is wired to ST-Link only

• NUCLEO-F072RB on DigiKey Japan - Board purchase

• SparkFun STUSB4500 Arduino Library - Alternative MCU-based programming

• GitHub: usb-c/STUSB4500 - Official ST reference code with NVM flasher

• STUSB4500 Datasheet - NVM register map details

• Pogo Pin Clip (AliExpress) - 4P 2.54mm programming clip tool

• PCBA v2 Debug Report - CC1DB internal short failure mode discovered during v2 testing