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The ST1VAFE3BX is an active STMicroelectronics mixed-signal biosensing IC that combines a single-channel differential vertical analog front end (vAFE) for biopotential signals with a synchronized three-axis accelerometer and on-chip processing. It can digitize ECG-, EEG-, ENG- and other electrode-based signals while motion data supplies context for artifact handling and activity detection. It is a component, not a complete medical monitor: electrodes, mechanics, power, firmware, algorithms and any required clinical validation remain part of the product designer’s job.
ST lists the device in volume production as order code ST1VAFE3BXTR, in a 12-lead LGA package measuring up to 2.0 × 2.0 × 0.74 mm. See the ST product page and current datasheet for revision-controlled details.
What the ST1VAFE3BX actually is
“vAFE” is ST’s term for a vertical analog front end intended to acquire biopotential signals through external electrodes. The chip provides one programmable differential channel, an internal 12-bit ADC, a three-axis accelerometer, a FIFO and embedded finite-state-machine (FSM), machine-learning-core (MLC) and adaptive self-configuration (ASC) functions. Digital data is available over I²C, SPI or MIPI I3C.
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The important architectural feature is synchronized electrical and motion sensing in one small IC. A host or embedded algorithm can compare body movement with changes in the electrode signal instead of treating the accelerometer as an unrelated sensor. That can support motion-aware interpretation, event detection and lower host data traffic, but it does not guarantee clean signals during vigorous movement or provide a diagnosis.
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At-a-glance specifications
| Item | Verified value |
|---|---|
| Status and order code | Active, volume production; ST1VAFE3BXTR |
| Package | 12-lead LGA; maximum 2.0 × 2.0 × 0.74 mm |
| Operating temperature | −40°C to +85°C |
| Supply | 1.62–3.6 V; MIPI I3C I/O supports 1.08–3.6 V |
| vAFE | Single-channel differential input, programmable gain and input impedance, 12-bit ADC |
| vAFE output data rate | Up to 3,200 Hz when the analog-hub/vAFE channel is used alone |
| Accelerometer | Three axes; ±2g, ±4g, ±8g or ±16g; 1.6–800 Hz ODR |
| Accelerometer noise | Down to 220 µg/√Hz |
| Typical current | 48.1 µA in high-performance mode; 2.6 µA in power-down |
| FIFO | Up to 128 combined accelerometer and vAFE samples, or 256 low-resolution accelerometer samples |
| Interfaces | I²C, SPI and MIPI I3C |
| Shock survivability | 10,000g |
These are typical or maximum specifications where indicated, not guarantees of end-product performance. The 3,200 Hz figure applies to the vAFE in its specified standalone analog-hub mode. The accelerometer tops out at 800 Hz, while MLC and FSM processing on analog-hub/vAFE data is specified up to 1.6 kHz.
How the signal path works
- Electrodes: External electrodes contact the body and feed the single differential vAFE input. Electrode placement, impedance, protection and mechanical pressure strongly affect noise.
- Analog front end and ADC: Programmable gain and input impedance condition the biopotential signal before the internal 12-bit conversion.
- Motion reference: The three-axis accelerometer samples movement on the same device, allowing firmware or embedded logic to correlate motion with electrical changes.
- Local buffering and processing: FIFO storage, motion events, FSM rules and MLC feature/classification processing can reduce interrupt and host-MCU workload.
- Host integration: An MCU receives raw or processed data over I²C, SPI or MIPI I3C and performs application-level filtering, feature extraction, user-interface and connectivity tasks.
What signals and applications are realistic?
ST identifies ECG, EEG and ENG applications, and distributor material also mentions EOG. These labels describe signal-acquisition use cases, not certification or guaranteed clinical accuracy. Heart rate, HRV, neurological features, eye movement or activity states are derived by application algorithms from the captured electrical and motion data.
- ECG wearables: patches, chest bands and other one-channel designs where motion context is useful.
- EEG or ENG research and monitoring: applications that can work with one differential channel and carefully controlled electrode arrangements.
- EOG and gesture systems: eye or muscle-related biopotentials combined with motion or orientation events.
- Portable well-being and activity products: low-power devices that need local event detection rather than continuous raw streaming.
A single differential vAFE channel is a fundamental limitation. Multi-lead ECG, high-channel-count EEG or specialized clinical instrumentation may require a dedicated multi-channel AFE instead.
Why synchronize the accelerometer?
Body movement, strap motion, electrode cable movement and mechanical vibration can create artifacts that overlap a physiological signal. A time-aligned accelerometer stream gives an algorithm a motion reference for detecting likely contamination, changing operating modes or applying a compensation strategy. The result is potentially better context and lower latency; it is not automatic artifact removal. Electrode adhesion, skin preparation, grounding and mechanical design can dominate performance during exercise.
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MLC, FSM and ASC explained
Machine-learning core (MLC)
The MLC can execute selected feature-processing or classification workloads inside the sensor. ST specifies operation on analog-hub/vAFE data up to 1.6 kHz. It is an embedded inference resource, not an autonomous medical-AI system.
Finite-state machine (FSM)
The programmable FSM handles deterministic event and signal-processing logic, also with analog-hub/vAFE input specified up to 1.6 kHz. It is useful for threshold sequences, timing conditions and low-power state changes.
Adaptive self-configuration (ASC)
ASC can change sensor configuration in response to FSM or MLC output. A design might use that capability to switch operating modes or reduce activity when conditions permit, but the behavior still has to be designed, tested and validated.
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Power, sampling and interface decisions
ST quotes 48.1 µA typical sensor current in high-performance mode and 2.6 µA typical in power-down. Older promotional material rounds these figures differently; the current datasheet is the better reference for design calculations. These are sensor currents, not complete wearable power. Add the electrode interface, regulator losses, MCU, radio, display, haptics, FIFO activity and interrupt handling.
Do not select 3,200 Hz merely because it is the highest number. A higher rate increases data volume and processing demand, while the accelerometer has an 800 Hz ceiling and embedded MLC/FSM processing is specified to 1.6 kHz. Confirm permitted synchronized-rate combinations in the datasheet.
- I²C: practical for straightforward sensor buses and moderate throughput.
- SPI: attractive when deterministic transfers or higher practical throughput matter.
- MIPI I3C: useful only when the host, board and software stack support it; it is not automatically lower power or lower cost in every design.
A practical integration sequence
- Define the signal: choose ECG, EEG, ENG, EOG or another biopotential target; document amplitude, bandwidth, electrode count and reference arrangement.
- Read the current documentation: use the datasheet and linked ST application notes for register limits, filtering and timing.
- Choose the bus and host: check MCU support, interrupt pins, FIFO-drain timing, sustained data rate and whether simultaneous motion/vAFE samples are required.
- Configure the vAFE: set gain, input impedance, data rate, filtering, antialiasing behavior, FIFO and interrupts for the actual electrodes rather than copying a universal setting.
- Configure motion: select accelerometer range, ODR, event functions, timestamps and interrupt behavior for expected movement and shock.
- Partition algorithms: decide what belongs in host firmware, FSM, MLC or a hybrid pipeline.
- Validate the assembled system: test open and shorted inputs, known electrical waveforms, electrode variation, sweat, cable motion, radio noise, temperature, battery/charger interference and long FIFO runs.
The 2 mm LGA saves board area but makes prototype probing, inspection, rework and routing harder. Follow ST’s mounting and soldering guidance and confirm that your assembler can achieve the required yield.
What is included—and what is not
| Included in the IC | Still required in the product |
|---|---|
| Single-channel vAFE, ADC and programmable analog settings | Electrodes, skin-contact mechanics and protection |
| Three-axis accelerometer and motion-event functions | PCB layout, grounding, power regulation and enclosure |
| FIFO, FSM, MLC, ASC and digital interfaces | Host firmware, application algorithms and wireless/UI functions |
| Self-test capability | System verification, safety work and any medical-device validation |
The part is therefore a building block, not a drop-in ECG monitor, electrode assembly, finished module or certified medical subsystem.
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Where it fits—and where it does not
Strong fit
- One biopotential channel plus synchronized motion in a very small wearable.
- Low sensor current and local event or classification processing.
- Products whose host MCU supports I²C, SPI or MIPI I3C.
- Teams able to design electrode mechanics and validate motion artifacts.
Reasons to choose another architecture
- Several independent differential channels or specialized lead-off and diagnostic functions are mandatory.
- You need a ready-to-use sensor module rather than a bare LGA IC.
- The team lacks biopotential, electrode and low-noise PCB experience.
- A simple accelerometer plus a dedicated AFE would meet requirements with less embedded-software complexity.
A dedicated multi-channel AFE offers more analog flexibility but may need a separate accelerometer. Separating the motion sensor and AFE also makes replacement easier, at the cost of more components and system-level synchronization. No alternative is universally better; compare channel count, input architecture, noise, current, tools, package and supply.
Availability and buying signals
ST’s eStore listing for ST1VAFE3BXTR was shown as active and in stock, with free-sample eligibility and a displayed signal of $2.20 per unit at quantity 100 on August 18, 2026. Price, stock, taxes and fulfillment vary by region and account.
DigiKey’s product-highlight page showed 7,409 units and a $3.58 price signal on that date; confirm the current quantity break and checkout total. ST’s product page did not return distributor availability at the time checked, so production buyers should obtain a current quotation. A $1.50 price for 1,000-unit orders appeared in ST’s October 28, 2024 announcement at ST newsroom; that is historical, not a current guaranteed quote.
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Choose the ST1VAFE3BX when your product needs one differential biopotential channel, synchronized three-axis motion and low-power edge processing in a tiny package. Treat it as an enabling IC: the electrodes, mechanics, analog hygiene, firmware and validation determine whether the final wearable works. For multi-channel clinical instrumentation or a ready-made certified subsystem, use a different architecture.
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