Ncv7240-driver

NCV7240 x4 — ESP32 + USB-C PD EPR (24 V) Driver Board

A KiCad 8 project for a compact controller board that:

• Negotiates 24 V from a USB-C PD 3.1 EPR source via the AP33772S sink controller.
• Hosts an ESP32-S3 MCU for Wi-Fi/BT control, configuration and host comms.
• Drives 32 low-side switched outputs at 24 V using 4 × NCV7240 octal low-side drivers (SPI-controlled).

Status: skeleton — project files, design rules, net classes and BOM are in place. The schematic (ncv7240-driver.kicad_sch) and PCB (ncv7240-driver.kicad_pcb) are intentionally empty placeholders ready to be populated in KiCad 8.

1. System architecture

       USB-C (PD 3.1 EPR, up to 28 V / 5 A)
           │
           ▼
   ┌────────────────┐   I²C   ┌──────────────────────┐
   │   AP33772S     │◀───────▶│   ESP32-S3-WROOM-1   │
   │  PD EPR sink   │  (CFG)  │  (Wi-Fi / BT / USB)  │
   └──────┬─────────┘         └───────┬──────────────┘
          │ VBUS_OUT = 24 V           │ SPI (CS x4, SCK, MOSI, MISO)
          │                           │ + RSTB, /FSO IRQ
          ▼                           ▼
   ┌──────────────┐   ┌──────────────┐   ┌──────────────┐   ┌──────────────┐
   │  NCV7240 #1  │   │  NCV7240 #2  │   │  NCV7240 #3  │   │  NCV7240 #4  │
   │ 8 ch low-side│   │ 8 ch low-side│   │ 8 ch low-side│   │ 8 ch low-side│
   └──────┬───────┘   └──────┬───────┘   └──────┬───────┘   └──────┬───────┘
          ▼                  ▼                  ▼                  ▼
       OUT1..8            OUT9..16          OUT17..24          OUT25..32
       (loads sink to GND; common rail = 24 V)

• The AP33772S handles all CC negotiation/PPS/EPR; the ESP32 just configures the request profile over I²C and reads VBUS / status telemetry.
• The 4 NCV7240s share SCK/MOSI/MISO/RSTB/SI on a single SPI bus; each has its own /CSB from the ESP32. Output enable is per-channel via SPI control word.

2. Bill of materials (core)

Plus per-channel flyback diodes/TVS if driving inductive loads (the NCV7240 has internal active clamp, but external TVS to 24 V rail is recommended for solenoids/relays).

3. Net classes / design rules

Defined in ncv7240-driver.kicad_pro:

4. Pin assignment (ESP32-S3 → NCVs / AP33772S)

Avoid the strapping pins (GPIO0/3/45/46) and USB pins (19/20) for the dedicated nets above — already accounted for.

5. NCV7240 wiring notes

• Tie all V_PWR pins to the 24 V rail through individual ferrite beads
  • 100 nF + 10 µF local decoupling per IC.
• All GND pins tied to the solid 24 V-return ground pour.
• SO is open-drain; place one 10 kΩ pull-up to 3V3 on the shared MISO net.
• /RSTB shared and pulled up to 3V3 (10 kΩ); ESP32 drives low to reset all.
• /FSO shared open-drain fault flag → ESP32 IRQ, pulled up to 3V3.
• Daisy-chained SPI is not used here (independent /CSB per device is simpler and lets the ESP32 talk to any device individually at full clock).
• Each OUTx pad gets a generous copper pour and a screw terminal or 2.54 mm header per channel. For inductive loads, place a TVS/clamp diode from OUTx to the 24 V rail close to the load connector.

6. AP33772S notes

• Connect CC1/CC2 directly to the USB-C receptacle CC pins (no Rd needed — the AP33772S provides the sink termination).
• VBUS sense via internal divider; place 100 µF + 10 µF + 100 nF bulk on VBUS_OUT after the controller's NMOS pass switch.
• Pull VPP / VDD decoupling per datasheet (1 µF on VDD, 100 nF on VPP).
• The MCU configures the requested PDO (request 24 V/3 A EPR profile) via I²C at boot. Until configured the AP33772S falls back to its NVM defaults — flash the NVM with the desired default PDO request before deployment if you want the rail to come up without the ESP32.
• Add a SMBJ33A TVS across VBUS_OUT to GND.

7. Layout guidance

• 4-layer stack recommended: Signal / GND / 24 V / Signal.
• Keep the 24 V rail as a continuous pour on an inner layer; stitch with vias near each NCV7240 V_PWR pin.
• USB-C D+/D- routed as a 90 Ω differential pair, length-matched, away from the switching loads. (For PD-only operation D± are unused but route them anyway so the port can carry USB 2.0 data if desired.)
• Place the AP33772S close to the USB-C connector; keep the VBUS path short and wide (≥ 60 mil for 5 A).
• ESP32 antenna keep-out: leave ≥ 15 mm clearance and no copper under the antenna section of the module.
• Per-channel output traces: 0.8 mm minimum for 0.5 A loads, scale up for more. Add 2× thermal-relief pads at each NCV7240 exposed pad.

8. Loads — Bürkert Type 0127 valves (inductive)

Outputs drive Bürkert Type 0127 rocker solenoid valves (24 V DC, 3 W ⇒ ≈125 mA per coil). 32 channels × 125 mA = 4 A peak on the 24 V rail — that's why we request a 24 V / 3-5 A EPR profile from the source.

Because the loads are inductive, every output has a B260A-13-F Schottky (60 V / 2 A, SMA) freewheel diode:

Anode → OUTx, Cathode → +24V rail.

When the NCV7240's low-side switch opens, the coil's collapsing field drives OUTx above +24 V; the diode forward-biases at ≈0.7 V and recirculates the coil current back into the rail, clamping OUTx to roughly +24V + Vf. This is faster and dissipates less per-event than relying on the NCV7240's internal active clamp (≈45 V).

Place the freewheel diodes physically close to the screw terminal pads so the loop area between coil, diode and ground is minimised — important for EMI on a board switching 32 inductive loads.

9. Files

ncv7240-driver/
├── .gitignore
├── README.md
├── fp-lib-table  /  sym-lib-table
├── ncv7240-driver.kicad_pro   # KiCad 8 project, design rules + net classes
├── ncv7240-driver.kicad_sch   # generated by tools/gen_sch.py
├── ncv7240-driver.kicad_pcb   # generated by tools/gen_pcb.py
├── datasheets/                # versioned vendor PDFs
│   ├── ncv7240.pdf            (onsemi)
│   ├── ap33772s.pdf           (Diodes Inc)
│   ├── esp32-s3-wroom-1.pdf   (Espressif)
│   ├── b260a.pdf              (Diodes Inc — flyback Schottky)
│   └── burkert-0127.pdf       (Bürkert — load)
└── tools/
    ├── gen_sch.py             # deterministic schematic generator
    └── gen_pcb.py             # deterministic PCB skeleton generator

Regenerate after editing the generators:

python3 tools/gen_sch.py > ncv7240-driver.kicad_sch
python3 tools/gen_pcb.py > ncv7240-driver.kicad_pcb

Open ncv7240-driver.kicad_pro in KiCad 8.0 or newer. In Pcbnew:

1. Tools → Update PCB from Schematic to import all 30+ footprints from the standard KiCad libraries (you'll need them installed locally — they ship with KiCad).
2. Components arrive at the origin; drag them into the marked floorplan zones (visible on User.Comments).
3. Route, fill the GND and +24V zones, run DRC, export Gerbers to gerbers/.

10. Board floorplan (160 × 100 mm, 4-layer)

+----------------------------------------------------------------------+
|              NCV7240 x4 Driver — 24V PD EPR    (silkscreen header)   |
|                                                                      |
|  +--------+ +-------------+ +-------------+ +--------+ +----------+  |
|  |USB-C PD| | Buck 24V→3V3| |             | |  4×    | |  Screw   |  |
|  |  J1 U1 | |  U7 L1 C3   | |  ESP32-S3   | | NCV    | |  termi-  |  |
|  | C1/C2  | +-------------+ |   U2        | | 7240   | |  nals    |  |
|  |  D1    |                 | C4 C5       | | U3-U6  | | J2..J5   |  |
|  |        | (44-90, 6-36)   | R1..R5      | |        | |          |  |
|  |        |                 |             | |        | |          |  |
|  |        | +-------------+ |             | +--------+ +----------+  |
|  |        | |             | |             | | Flyback diode field   |  |
|  |        | |    ESP32    | |             | | D2..D33  B260A-SMA    |  |
|  | (4-44, | |  (44-90,    | | (44-90,     | | (90-156,              |  |
|  |  6-60) | |   36-96)    | |  36-96)     | |  60-96)               |  |
|  +--------+ +-------------+ +-------------+ +--------+ +----------+  |
|                                                                      |
+----------------------------------------------------------------------+

4-layer stackup: F.Cu / GND / +24V / B.Cu (1.6 mm FR4, ENIG finish).

9. License

Hardware: CERN-OHL-S v2 (recommended) — adjust to your needs.