Nordic Semiconductor nRF5340 + nRF7002
Compact Wearable IoT Device
Overview
A compact, battery-powered wearable device featuring Wi-Fi and Bluetooth connectivity for portable applications.
OmsinghSystem architecture
POWER
MCU
RF
SENSOR
MISC
- POWER_MANAGEMENT → MCU_SOCPowerRegulated core supply rail from PMIC buck output
- POWER_MANAGEMENT → BATTERY_GAUGEI2CFuel gauge communication and monitoring
- BATTERY_GAUGE → MCU_SOCI2CBattery state of charge reporting to application processor
- MCU_SOC → SENSORSI2CIMU sensor data collection and interrupt signaling
- MCU_SOC → RF_WIRELESSRFAntenna feed line with Pi-matching network for Wi-Fi and Bluetooth
- MCU_SOC → USER_IOGPIOUser button input detection and status LED drive
Bill of materials
| Part number | Type | Component | Manufacturer | Package | Qty | Datasheet | Match |
|---|---|---|---|---|---|---|---|
| BQ25120 | POWER | Texas Instruments BQ25120A Li-ion battery linear charger with integrated low-Iq buck converter and LDOs | TI | DFN22-10 | 1 | Matched | |
| BQ27421 | POWER | Texas Instruments BQ27421-G1A System-side impedance tracking State-of-Charge (SoC) reporting | Texas Instruments | — | 1 | Matched | |
| nRF7002-EB | MCU | Nordic Semiconductor nRF5340 + nRF7002 Dual-core application processor with dedicated BLE subsystem and low-power Wi-Fi 6 companion chip | Nordic Semiconductor ASA | - | 1 | Matched | |
2 alternatives consideredAI verified | |||||||
| 2400AT43A5600E | RF | Custom Ceramic Chip Antenna with Pi-matching Provides tuned 2.4GHz / 5GHz resonance close to human tissue | Various | — | 1 | Pending | |
2 alternatives consideredAI verified | |||||||
| LSM6DSOXTR | SENSOR | STMicroelectronics LSM6DSOX Ultra-low power 3D accelerometer and 3D gyroscope with embedded machine learning core | STMicroelectronics | 14-VFLGA Module | 1 | Matched | |
| RGB LED x1 | MISC | Single Tactile Switch & RGB Status LED User input for power state / pairing mode and visual feedback | Raspberry Pi | — | 1 | Matched | |
4 alternatives consideredAI verified | |||||||
Build guide
6-8 hoursAdvanced
1
Procurement & Preparation
- Procure all surface-mount components including BQ25120, BQ27421, nRF7002-EB, 2400AT43A5600E ceramic antenna, LSM6DSOXTR accelerometer, and RGB tactile switch according to the BOM.
- Prepare the PCB stencil and apply Type 4 lead-free SAC305 solder paste to the wearable IoT device circuit board pads.
2
Hardware Assembly & Wiring
- Place the Texas Instruments BQ25120 charger, BQ27421 fuel gauge, and Nordic nRF5340 + nRF7002 MCU chipset onto their respective paste-applied landing pads.
- Place the STMicroelectronics LSM6DSOXTR 6-axis IMU, the custom ceramic chip antenna (2400AT43A5600E) with Pi-matching network, and the tactile switch with integrated RGB LED.
- Pass the populated PCB assembly through a reflow oven following the SAC305 thermal profile (peak temperature 245°C).
- Inspect solder joints under an optical microscope or X-ray machine, then clean flux residues using isopropyl alcohol (IPA).
3
Firmware Setup
- Connect the SWD programmer to the nRF5340 debug pins on the wearable PCB and flash the primary application bootloader.
- Compile and flash the Nordic nRF Connect SDK firmware supporting BLE stack initialization, Wi-Fi 6 driver routines, BQ27421 I2C fuel gauge polling, and LSM6DSOX machine learning core configurations.
4
Testing & Calibration
- Perform quiescent current (Iq) and power rail verification on the 3V3 output from the BQ25120 using a digital multimeter and DC power analyzer.
- Calibrate the BQ27421 impedance tracking State-of-Charge (SoC) reporting engine and test battery charging cycles.
- Verify 2.4GHz / 5GHz RF performance of the ceramic chip antenna and Pi-matching network using a vector network analyzer (VNA) and test BLE/Wi-Fi connection stability.
- Validate LSM6DSOX inertial sensor data stream and test the tactile switch and RGB LED user interface feedback states.
Document
Compact Wearable IoT Device
A compact, battery-powered wearable device featuring Wi-Fi and Bluetooth connectivity for portable applications.
Design Overview
| Item | Details |
|---|---|
| Product Type | Wearable IoT Device |
| Key Functions | Wireless connectivity via Wi-Fi and Bluetooth, Rechargeable Li-ion battery power management, Compact wearable operation |
| Power Source | Rechargeable Li-ion battery |
| Connectivity | Wi-Fi, Bluetooth |
| Size | Compact / Miniature |
| Environment | wearable |
| Difficulty | Advanced |
| Est. Time | 6-8 hours |
System Architecture
Power Topology: Single-cell Li-ion battery (3.7V nominal, 300-500mAh) connected to BQ25120A PMIC, stepping down to a clean 3.3V main rail via integrated low-quiescent buck converter, supplying MCU, wireless subsystems, and sensors.
Module List
| Module ID | Type | Name | Function | Voltage |
|---|---|---|---|---|
| POWER_MANAGEMENT | POWER | Texas Instruments BQ25120A | Li-ion battery linear charger with integrated low-Iq buck converter and LDOs | 3.7V |
| BATTERY_GAUGE | POWER | Texas Instruments BQ27421-G1A | System-side impedance tracking State-of-Charge (SoC) reporting | 3.3V |
| MCU_SOC | MCU | Nordic Semiconductor nRF5340 + nRF7002 | Dual-core application processor with dedicated BLE subsystem and low-power Wi-Fi 6 companion chip | 3.3V |
| RF_WIRELESS | RF | Custom Ceramic Chip Antenna with Pi-matching | Provides tuned 2.4GHz / 5GHz resonance close to human tissue | 3.3V |
| SENSORS | SENSOR | STMicroelectronics LSM6DSOX | Ultra-low power 3D accelerometer and 3D gyroscope with embedded machine learning core | 3.3V |
| USER_IO | MISC | Single Tactile Switch & RGB Status LED | User input for power state / pairing mode and visual feedback | 3.3V |
Design Schemes
Dual-Core Wireless SoC with Advanced PMIC ★
Utilizes a dual-core application and wireless SoC paired with a low-quiescent PMIC and custom ceramic antenna for compact skin-contact wearability.
Trade-offs: Optimizes PCB footprint and skin-temperature dissipation better than discrete multi-chip solutions, while maintaining high Wi-Fi/BLE performance.
Single-Chip RISC-V IoT Architecture
Employs an all-in-one RISC-V SoC with integrated Wi-Fi 6, BLE, and 802.154 for ultra-compact, cost-optimized wearable production.
Trade-offs: Lower BOM cost and reduced PCB complexity, but relies on a single processing core for both application and wireless duties.
Key IC selection
dual-core application processor and wireless companion
- Need: Provide dual-core processing for real-time BLE stack execution, application logic, and low-power Wi-Fi 6 interfacing within a constrained wearable power envelope.
- Class: Dual-core ARM Cortex-M33 SoC with companion Wi-Fi 6 companion IC
- Shortlist: Nordic nRF5340 + nRF7002, Realtek RTL8730EH, Espressif ESP32-H2 + ESP32-C6 (multi-chip approach)
- Pick: Select based on Bluetooth LE multiprotocol maturity, ultra-low sleep current consumption, combined solution footprint, and unified software ecosystem support.
battery charger and power management IC
- Need: Provide safe linear charging for a small Li-ion cell while generating highly efficient low-Iq step-down and LDO rails for the MCU and sensors.
- Class: Linear Li-ion battery charger with integrated nano-power buck converter and LDOs
- Shortlist: Texas Instruments BQ25120A, Analog Devices LTC4124, Maxim Integrated MAX77650
- Pick: Choose based on quiescent current in ship mode, programmable output voltage steps, integrated protection features, and ultra-small WQFN package size.
dual-band antenna matching and radiation
- Need: Radiate and receive 2.4GHz (BLE/Wi-Fi) and 5GHz (Wi-Fi 6) RF energy efficiently while minimizing detuning effects caused by proximity to human tissue.
- Class: SMD ceramic chip antenna with discrete Pi-matching network
- Shortlist: PulseLarsen W3027 / similar dual-band ceramic chip, Taoglas FXP830 flexible PCB antenna, Yageo / TDK multilayer ceramic chip antennas
- Pick: Select based on clearance requirements, omnidirectional gain profile, small footprint, and empirical VNA tuning performance on the final wearable mechanical enclosure.
Risk register
| ID | Area | Severity | Detail | Mitigation |
|---|---|---|---|---|
| r1 | rf | high | Human tissue proximity to the ceramic chip antenna significantly detunes the 2.4GHz/5GHz Pi-matching network, degrading Wi-Fi throughput and BLE link budget. | Perform antenna tuning and impedance sweeps using a specific wrist/body phantom model; allocate adequate board space for a robust Pi-matching network close to the feed point. |
| r2 | thermal | med | High peak current consumption during Wi-Fi 6 packet transmission on the nRF7002 can cause localized heating and accelerated battery voltage sag in a compact wearable enclosure. | Implement aggressive duty-cycling in firmware, optimize Wi-Fi TX power levels, and ensure the BQ25120A buck rail layout has low parasitic resistance to handle peak transient loads. |
| r3 | emi | med | High-frequency switching noise from the BQ25120A integrated buck converter may couple into the adjacent LSM6DSOX sensor lines or desense the 2.4GHz/5GHz receiver. | Keep input and output filter capacitors physically close to the PMIC pins, use a solid internal ground plane reference, and route sensitive analog/sensor lines away from high-di/dt switching loops. |
Key Components
5/6 modules matched to real parts. See the BOM tab for the full component table.
Texas Instruments BQ25120A (BQ25120)
The candidate BQ25120 matches the primary MPN BQ25120A (base part number match with acceptable ordering suffix differenc
Texas Instruments BQ27421-G1A (BQ27421)
The candidate matches the primary MPN BQ27421 and belongs to the correct component class (Integrated Circuits) from Texa
Nordic Semiconductor nRF5340 + nRF7002 (nRF7002-EB)
Candidate 2 is an evaluation board (nRF7002-EB) from Nordic Semiconductor corresponding to the primary MPN nRF7002.
Custom Ceramic Chip Antenna with Pi-matching (2400AT43A5600E)
Web recommendation: 2400AT43A5600E (not in ES)
Build Summary
- Difficulty: Advanced
- Estimated time: 6-8 hours
- Tools required: Anti-static tweezers, Component storage trays, Solder paste stencil, Squeegee, Type 4 SAC305 Solder Paste, Precision vacuum pen
See the Build tab for the full step-by-step assembly guide.
Generated by YuanQi AI Design System · Query: Hardware design project based on the uploaded circuit schematic/image.