How to Maximise Battery Life with an Ultra-Low Power Bluetooth SoC: EM Microelectronic EM9305

Introduction – Why Battery Life Has Become the Most Critical Constraint in BLE Design

There is a contradiction at the heart of the IoT market. Bluetooth Low Energy devices are sold on the promise of long, largely maintenance-free operation. Yet for many product teams, battery life remains the single most persistent source of post-launch complaints, costly returns, and unplanned field maintenance. A smart sensor that needs a battery swap every eight months rather than every two years is not just inconvenient - it erodes product credibility and inflates lifetime support costs in ways that can dwarf the original hardware bill of materials.

The challenge is partly a benchmarking problem. Until recently, engineers comparing BLE SoCs across vendors were reliant on datasheet current figures measured under idealised laboratory conditions that rarely matched the power profile of a real application. Peak receive and transmit currents matter, but the actual energy consumed per advertising event integrated across sleep, wake, transmit, and return-to-sleep, is what determines how long a CR2032 coin cell lasts in a deployed device. No standardised, vendor-neutral methodology existed to make that comparison reliably.

That changed in late 2025 with the introduction of BlueJoule, the industry's first open and reproducible benchmark for real-world Bluetooth advertising energy efficiency. Developed by Bob Frankel of EM Foundation and Mohammad Afaneh of Novel Bits, BlueJoule provides an objective, verifiable testing framework that any engineer can reproduce. And, in its inaugural ranking, EM Microelectronic's em | bleu (EM9305) ultra-low power Bluetooth SoC took the top position by a substantial margin, delivering up to twice the battery autonomy of competing solutions from Nordic Semiconductor, Silicon Labs, and Texas Instruments across both major advertising profiles.

For Ineltek customers designing battery-powered connected devices, the EM9305 is worth a very close look.

What Makes the EM9305 Different

The EM9305 is a Bluetooth 5.4 SoC has been designed from the ground up around the premise that every microamp counts. That philosophy runs through every layer of the design, from the RF transceiver and power management system to the firmware scheduler and memory architecture.

At the RF level, the transceiver achieves receive current of 3.1mA and transmit current of 3.4mA at 0dBm in DCDC Step-Down configuration which are competitive figures in their own right. But the more significant numbers are in the sleep states. BLE sensors that broadcast environmental data, track assets, or monitor health metrics spend well over 99% of their time in sleep mode between advertising events. The EM9305's BLE sleep mode current is 390nA with crystal oscillator and 4kB RAM retention. Deep sleep drops further to 200nA, and chip disable mode is below 10nA. These are not theoretical minimums; they represent the power floor that governs the vast majority of operational time in a real always-on IoT device.

The power management system underpinning these figures is unusually flexible. The EM9305 supports 1.5V alkaline, zinc-air, and silver oxide batteries in step-up DCDC configuration, 3V lithium coin cells in step-down DCDC configuration, and direct USB 5V supply all within a single device. An inductor-less voltage multiplier mode for 1.5V batteries further reduces bill-of-materials cost and PCB complexity, which matters for cost-sensitive high-volume designs. The device operates down to 1.1V, which means it continues to extract useful energy from a battery well past the point where competing solutions would drop out.

The on-chip processor is an ARC EM7D 32-bit RISC core running at 48MHz, supported by a DSP pipeline and floating-point unit for audio and tracking algorithm execution, and a DMA controller that offloads data movement from the main CPU to further reduce active power consumption. A 2kB instruction cache reduces flash access cycles. All 64kB of SRAM can be retained during sleep in 4kB increments, allowing the firmware to tune retention to the exact amount needed - a feature that directly reduces sleep current by ensuring only necessary state is kept powered.

The complete Bluetooth 5.4 stack is implemented in 512kB of on-chip flash, with a 64kB ROM for secure boot and a certified Bluetooth 5.4 Controller Subsystem validated by the Bluetooth SIG. The link layer scheduler is designed to halt the CPU in all modes where computation is not required, waking only to service the next scheduled event. This architectural approach with CPU-off by default, wake-only-when-necessary is what enables the EM9305's sleep current advantage to translate so directly into the real-world battery life improvement demonstrated by BlueJoule.

The BlueJoule Benchmark and What the Results Mean

The BlueJoule benchmark addresses a problem that has long frustrated embedded engineers: the impossibility of meaningful cross-vendor BLE power comparison. Datasheet figures measure different things under different conditions, making it impossible to determine from published specifications alone which device will actually last longer in a deployed product.

BlueJoule establishes a consistent test methodology measuring energy consumption across the complete advertising cycle of sleep, wake, transmit, and return to sleep under two representative real-world scenarios: an always-on sensor profile using longer advertising intervals representative of broadcast-and-sleep devices, and a real-time asset tracking profile using more frequent advertising intervals that demand higher update rates. Results are expressed in EM•eralds, where one point equates to approximately one month of operation from a CR2032 coin cell, giving product teams an immediately practical figure for estimating autonomy in the field.

In the inaugural ranking, the EM9305 led across both profiles, outperforming competing solutions from Nordic, Silicon Labs, and Texas Instruments by up to a factor of two. The benchmark's open and reproducible methodology means these results can be independently verified by any engineer representing a significant point of differentiation from vendor-supplied claims. The BlueJoule results also align with EM Microelectronic's deployed user-base: over 500 million devices have been shipped using the EM9305's predecessor in the field, providing extensive real-world validation of the power architecture that the EM9305 inherits and extends.

For design teams working to meet battery life targets, the practical implication is direct: for a given coin cell battery and advertising interval, the EM9305 extends device service life by a factor of approximately two compared to the leading competing solutions, which translates directly into reduced maintenance frequency, lower total cost of ownership, and improved product differentiation.

Technical Specifications

Parameter	Specification
Bluetooth Standard	Bluetooth 5.4 (Bluetooth SIG Certified Controller Subsystem)
Processor	ARC EM7D 32-bit RISC, 48MHz, with DSP and FPU
Flash Memory	512kB (application, stack, profiles) + 32kB information area
RAM	64kB (all retainable, 4kB minimum retention increment)
ROM	64kB (secure boot)
Cache	2kB instruction cache
RX Current	3.1mA typical at 3V, DCDC Step-Down
TX Current	3.4mA typical at 0dBm, 3V, DCDC Step-Down
BLE Sleep Current	390nA with XTAL, 4kB RAM retention
Deep Sleep Current	200nA (no RAM retention)
Disable Mode Current	<10nA
RX Sensitivity	-97dBm at 1Mbps (37-byte payload); -103dBm at 125kbps; -94dBm at 2Mbps
TX Output Power	-28dBm to +10dBm (programmable); +10dBm version available
Supply Voltage	1.1V to 3.6V (battery); 4.4V–5.25V (USB, QFN/die only)
Battery Support	Li/MnO2 3V, Alkaline 1.5V, Zinc-Air 1.4V, Silver Oxide 1.55V
Interfaces	SPI (master/slave), I2C (master), UART, I2S/TDM, USB (QFN/die only), GPIO
Security	AES-128 hardware encryption, TRNG, ECC-P256 key generation, secure FOTA, secure lifecycle management
BLE Features	LE 2M PHY (HDR), LE Coded PHY (Long Range), AoA/AoD Direction Finding, Isochronous Channels (LE Audio), PAwR, ESL
Simultaneous Connections	Up to 4
Package Options	QFN-28 (4x4mm), WLCSP23 (1.8x1.8mm), bare die/wafer
Operating Temperature	-40°C to +85°C
Certifications	Bluetooth SIG BLE 5.4 Controller Subsystem; CE/FCC certification support available

Industry Applications and Use Cases

Wearables and Ultra-Compact Connected Devices

The EM9305's 1.8 x 1.8mm WLCSP23 package is among the smallest Bluetooth SoC footprints available anywhere in the market. Combined with its sleep current performance, this makes the EM9305 the enabling component for a category of connected devices that previously required engineering compromises: smart rings, connected pens, hearing aids, jewellery with embedded sensing, and next-generation medical wearables where PCB area is constrained to single-digit square millimetres. The inductor-less voltage multiplier mode for 1.5V batteries eliminates the need for an external DCDC inductor, saving additional board area and reducing assembly complexity.

Healthcare Monitoring and Medical IoT

Continuous health monitoring devices like glucometers, cardiac patch monitors, temperature loggers, activity trackers for clinical trials, operate in environments where battery replacement is either inconvenient or just plain impractical. The EM9305's validated autonomy advantage under the BlueJoule benchmark, combined with its full Bluetooth 5.4 implementation including isochronous channels for LE Audio, positions it for both data-centric monitoring applications and emerging audio-enabled medical devices. The WLCSP package and industrial temperature rating also support the move towards body-worn devices that must operate reliably across the full range of human physiological environments.

Asset Tracking and Logistics

Real-time asset tracking tags broadcast frequently to ensure reliable detection, which makes energy-per-advertising-event the dominant factor in battery life. The EM9305's performance in the BlueJoule real-time tracking profile - the more demanding of the two benchmark scenarios - demonstrates its suitability for this application directly. Bluetooth 5.4 Direction Finding (AoA/AoD) support enables sub-metre location accuracy without additional RF hardware, supporting both entry-level tracking and high-precision positioning applications from the same device. Periodic Advertising with Responses (PAwR) and Electronic Shelf Label (ESL) support further extend the addressable use cases into retail and warehousing.

Industrial and Building IoT Sensors

Wireless sensors deployed in industrial automation, smart building management, and predictive maintenance applications typically operate from primary batteries with expected service lives measured in years. The EM9305's companion IC mode allows it to be connected to any MCU or ASIC via SPI or UART HCI, adding Bluetooth connectivity to an existing sensor design without requiring a complete platform redesign. Its operating temperature range of -40°C to +85°C covers the majority of industrial and building environments. The security feature set - AES-128, TRNG, ECC-P256, and secure FOTA - meets the expectations of industrial customers who require over-the-air firmware updates with cryptographic authentication.

Consumer Electronics and Smart Home Devices

Wireless mice, keyboards, remote controls, smart locks, and home automation sensors represent the highest-volume segment of BLE deployment. In this category, bill-of-materials cost and battery life together determine product success. The EM9305's inductor-less operation mode and minimal external component count reduce system cost, while its validated autonomy advantage directly supports the multi-year battery life claims that differentiate premium consumer products. With over 500 million units of the predecessor device shipped, EM Microelectronic's manufacturing reliability and volume supply capability are well established for high-volume consumer programmes.

Conclusion – The EM9305 Ultra-Low Power Bluetooth SoC

The introduction of the BlueJoule benchmark has done something genuinely useful for the BLE industry: it has replaced anecdotal comparisons and conflicting datasheet figures with a reproducible, vendor-neutral measurement that engineers can trust. And in that first ranking, the EM Microelectronic EM9305 has established itself as the most energy-efficient commercially available Bluetooth SoC for the advertising scenarios that matter most to IoT product designers.

For Ineltek customers, the EM9305 is available now in volume production. EM Microelectronic will be showcasing the device at Embedded World 2026, and Ineltek's team will be present to discuss application requirements, samples, and design support. Whether you are working on a new design from scratch or evaluating an upgrade to an existing BLE platform, the EM9305 is a device worth putting on your shortlist. Contact us to arrange a meeting at the show or to request samples.

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FAQ - The EM9305 Bluetooth SoC

Q. What makes the EM9305 the top-ranked Bluetooth SoC in the BlueJoule benchmark?

A. The EM9305 achieves its benchmark-leading performance through a combination of ultra-low sleep current (390nA with XTAL and 4kB RAM retention), an efficient CPU scheduler that halts the processor whenever computation is not required, granular RAM retention control in 4kB increments, and a power management system that supports multiple battery chemistries at their native voltage without unnecessary conversion losses. BlueJoule measures the complete advertising energy cycle including sleep, wake, transmit, and return to sleep - and it is the sleep current architecture that determines real-world battery life in deployed IoT devices.

Q. Can the EM9305 be used as a companion Bluetooth chip alongside an existing MCU?

A. Yes. In companion IC mode the EM9305 connects to any host MCU or ASIC via SPI or UART using the standard Bluetooth HCI interface, adding a complete Bluetooth 5.4 radio and stack to an existing design with minimal integration effort. In SoC mode it runs simple applications entirely on its internal ARC EM7D processor. Both modes are fully supported and documented.

Q. What battery types does the EM9305 natively support?

A. The EM9305 supports 3V lithium coin cells (including CR2032) in DCDC step-down mode, 1.5V alkaline, zinc-air, and silver oxide cells in step-up or voltage multiplier mode, and direct USB 5V supply. The voltage multiplier mode eliminates the external DCDC inductor, reducing BOM cost and PCB area for 1.5V battery designs.

Q. What Bluetooth 5.4 features does the EM9305 support?

A. The full Bluetooth 5.4 feature set is included: LE 2M PHY (High Data Rate), LE Coded PHY (Long Range), Angle-of-Arrival and Angle-of-Departure for direction finding, isochronous channels for LE Audio, Periodic Advertising with Responses (PAwR), and Electronic Shelf Label (ESL) support, along with secure FOTA and AES-128 hardware encryption.

Q. Which EM9305 package is best for ultra-compact applications such as smart rings?

A. The WLCSP23 package at 1.8 x 1.8mm is designed for the most space-constrained applications, including smart rings, hearing aids, connected jewellery, and miniaturised medical wearables. The QFN-28 at 4 x 4mm is the preferred choice for prototyping and standard PCB layouts. USB functionality is available only in QFN or bare die versions.