NX15 Hardware Design
This page provides the basic hardware design guidelines for integrating the NX15 Series BLE module into a host board.
It focuses on power, ground, GPIO usage, programming/debug access, reset, and PCB-level bring-up requirements.
This page does not cover antenna layout in detail. For chip antenna keep-out and u.FL RF trace design, see NX15 Antenna Design.
Hardware Design Flow
Use this checklist before finalizing the host PCB.
| Step | Design Area | Goal |
|---|---|---|
| 1 | Power input | Provide a stable supply within the recommended range |
| 2 | Ground | Connect all GND pads to a solid ground plane |
| 3 | Decoupling | Place bypass capacitors close to VDD pads |
| 4 | Programming / debug | Route SWDIO, SWDCLK, GND, and reset to accessible pads |
| 5 | Reset | Provide a reliable NRESET path |
| 6 | GPIO planning | Confirm pin function before PCB finalization |
| 7 | Interface routing | Route UART, SPI, I2C, PWM, ADC, or PDM as required |
| 8 | Bring-up access | Keep test points available for early validation |
Power Supply
NX15 uses VDD_nRF as the main supply input.
| Item | Recommendation |
|---|---|
| Supply range | 1.7 V to 3.6 V |
| Typical supply | 3.3 V |
| Power rail | Keep stable during radio TX/RX activity |
| Decoupling | Place 100 nF + 1 µF capacitors close to each VDD pad |
| Ground return | Use a short, low-impedance return path to the ground plane |
Do not use the absolute maximum rating as the normal design target. Design the product using the recommended operating range.
Ground Design
All GND pads should be connected to a solid ground plane.
| Rule | Why It Matters |
|---|---|
| Connect every GND pad | Prevents floating ground pads and unstable behavior |
| Use short vias to ground | Reduces impedance and improves RF / thermal return |
| Keep ground plane continuous | Helps RF performance and power stability |
| Avoid splitting ground below the module | Prevents unpredictable return current paths |
For BLE modules, ground design affects both electrical stability and RF performance. Treat the GND pads as part of the RF reference path, not only as power return.
Programming and Debugging
NX15 provides SWDIO and SWDCLK for firmware programming and debugging.
| Signal | Purpose | Recommendation |
|---|---|---|
| SWDIO | Serial Wire Debug data | Route to SWD header or test pad |
| SWDCLK | Serial Wire Debug clock | Route to SWD header or test pad |
| GND | Debug reference | Route to the same debug connector |
| NRESET | Reset control | Route to debug connector or test pad |
Keep these signals accessible during development and production.
Even if the final product does not expose a full debug connector, test pads are strongly recommended for firmware flashing, recovery, and production programming.
Reset Design
The NRESET pin is an active-low system reset signal.
| Item | Recommendation |
|---|---|
| Reset access | Route NRESET to a reset button or debug connector |
| Firmware recovery | Keep NRESET accessible during bring-up |
| Production test | Provide test pad access if no button is used |
| Pull-up / reset circuit | Follow the reference circuit recommendation |
A reliable reset path is important for firmware flashing, debugging, and board-level recovery.
GPIO and Interface Planning
NX15 GPIO pins can be mapped to different peripheral functions through firmware configuration.
| Interface | Typical Use |
|---|---|
| UART | Host communication, logging, simple command/data interface |
| SPI | External sensors, peripherals, or memory-related functions |
| I2C | Low-speed sensors and configuration devices |
| PWM | LED, buzzer, or control output |
| ADC | Analog sensor input |
| PDM | Digital microphone input |
| GPIO | Buttons, interrupts, enable pins, status lines |
GPIO availability depends on firmware configuration and module variant. On Flash models, verify whether QSPI-related pins are reserved before using them as general-purpose GPIO.
Analog Input Notes
Some pins can be used as analog input channels.
| Design Item | Recommendation |
|---|---|
| Analog traces | Keep away from noisy or high-speed signals |
| Input protection | Add protection if the signal comes from outside the board |
| Filtering | Add RC filtering when required by the sensor |
| Voltage range | Keep input voltage within allowed GPIO / ADC limits |
Clock / NFC / Special Function Pins
Some pins may have special functions depending on the firmware configuration.
| Pin Group | Possible Function | Design Note |
|---|---|---|
| XL1 / XL2 | 32.768 kHz LFXO or GPIO | Reserve if external low-frequency crystal is used |
| NFC1 / NFC2 | NFC antenna pins or GPIO | Keep as NFC pins if NFC is required |
| SWO | Debug trace or GPIO | Use as SWO only when debug trace is required |
| QSPI-related pins | External Flash function or GPIO | Check carefully on Flash models |
Basic PCB Design Rules
Use the following rules as the minimum hardware design checklist.
| Rule | Description |
|---|---|
| GND | Connect all GND pads to a solid ground plane |
| Decoupling | Place 100 nF + 1 µF capacitors near each VDD pin |
| RF area | Maintain antenna keep-out around the antenna edge |
| RF trace | Use 50 Ω controlled impedance for RF feed traces |
| Debug | Keep SWDIO, SWDCLK, GND, and NRESET accessible |
| Test points | Add test points for key power and debug signals |
Hardware Bring-up Checklist
Before applying power to the first prototype, check:
| Item | Status |
|---|---|
| VDD_nRF is within the recommended operating range | ☐ |
| All GND pads are connected to a solid ground plane | ☐ |
| Decoupling capacitors are placed close to VDD pads | ☐ |
| SWDIO and SWDCLK are accessible | ☐ |
| NRESET is accessible | ☐ |
| GPIO functions match firmware configuration | ☐ |
| Antenna area follows the correct layout rules | ☐ |
| Test points are available for debugging | ☐ |
What Not to Include Here
To avoid duplicate content, the following topics are handled in separate pages:
| Topic | Go To |
|---|---|
| Chip antenna keep-out and u.FL RF trace | NX15 Antenna Design |
| Sleep current and firmware power tuning | NX15 Low Power Guide |
| BLE advertising and GATT services | NX15 BLE Application Guide |
| Model variant selection | NX15 Module Integration / Model Selection |
| LGA pad detail | NX15 Module Integration / LGA Pad Layout |