SCHURTER introduces STTP 9550 three‑terminal fuse is a compact protection device specifically designed for lithium‑ion battery packs, combining conventional overcurrent protection with an actively triggered overcharge protection function.
This architecture enables battery designers to implement redundant, intelligent safety concepts that go beyond what standard two‑terminal fuses or protection ICs alone can provide. For engineers working on multi‑cell battery packs in tools, mobility, and stationary storage, the SCHURTER STTP intelligent fuse family offers a ready‑made building block to meet modern safety and reliability requirements.
Key features and benefits
- Combined passive and active protection
The STTP 9550 integrates a conventional current‑dependent fuse function with a separate trigger terminal for actively initiated disconnection, enabling both self‑acting and controlled protection in one device. - Active overcharge protection capability
The dedicated trigger terminal allows a battery management system (BMS) or safety controller to open the fuse deliberately in defined fault scenarios such as overcharge, over‑temperature, or detected component failure, rather than relying only on overcurrent thresholds. - Redundant safety path for protection IC/FET failure
By providing an additional disconnection path independent of the main protection IC or FETs, the three‑terminal design addresses single‑point‑of‑failure concerns in high‑energy Li‑ion packs and supports safety‑critical architectures. - Gold‑plated terminals for stable performance
Gold‑plated contacts help maintain low and stable contact resistance over life, improving efficiency and minimizing heat generation at the fuse interface, while also enhancing signal integrity when the device is used in monitored protection schemes. - Compact footprint for high power density packs
The package is optimized for space‑constrained battery designs, supporting packs from approximately 1 up to 24 series cells according to manufacturer documentation, which is key for portable and e‑mobility applications. - Support for modern safety standards
The STTP three‑terminal fuse concept is intended for use in redundant protection architectures as required by contemporary battery safety standards and UL approvals, helping design teams align with compliance and certification targets.
Typical applications
The STTP 9550 intelligent fuse has been designed with a broad range of Li‑ion battery‑based equipment in mind, where both energy content and safety requirements are increasing:
- Stationary and residential energy storage systems (ESS) and backup battery cabinets
- Uninterruptible power supplies (UPS) and industrial backup modules
- Power tools and cordless professional equipment
- E‑bikes and e‑scooters with multi‑cell battery packs
- Automated guided vehicles (AGVs) and other battery‑powered logistics platforms
- Compact battery modules for industrial and building automation
In these systems, the three‑terminal fuse can serve as the last line of defense against abnormal charge or discharge conditions while interacting closely with the BMS for intelligent fault handling. It fits particularly well in designs where high power density, tight packaging, and strict safety regulations converge.
Technical highlights
- Three‑terminal architecture
Two terminals act as the main current‑carrying path similar to a conventional fuse, while the third terminal is used to actively trigger disconnection under control of the BMS or protection circuitry. - Current‑dependent interruption
The primary fuse element is designed to open when current exceeds a defined threshold for a specified time, protecting against short circuits and severe overcurrents according to manufacturer datasheet values. - Actively triggered opening
When the trigger terminal is driven according to the recommended application circuit, the fuse can be opened independent of the instantaneous load current, enabling targeted interventions such as controlled pack shutdown. - Gold‑plated contact system
The gold‑plated terminals contribute to low contact resistance and high corrosion resistance, which is important in environments with temperature cycling, humidity, or long service life expectations. - Cell count flexibility
The STTP 9550 is specified for battery packs from single‑cell up to 24‑cell configurations according to manufacturer documentation, covering typical voltage ranges used in e‑mobility, tools, and small ESS modules.
Design engineers should consult the STTP datasheet for detailed electrical ratings, recommended operating conditions, and mechanical dimensions. Parameters such as rated current, breaking capacity, and time‑current characteristics must be aligned with the specific pack configuration and fault scenarios.
STTP 9550 application overview
| Parameter / aspect | Description |
|---|---|
| Protection functions | Overcurrent fuse plus actively triggered disconnection |
| Battery chemistry | Lithium‑ion battery systems |
| Supported series cell count | Approximately 1 to 24 cells (per manufacturer documentation) |
| Typical system categories | ESS, UPS, power tools, e‑bikes/e‑scooters, AGVs and mobile equipment |
Design‑in notes for engineers
- Define the protection concept early
Decide how the three‑terminal fuse will interact with your BMS and other safety components, including which fault states should trigger active disconnection (for example overcharge, over‑temperature, or detected FET short). - Coordinate current ratings with pack design
Select the fuse rating based on maximum continuous current, expected peak loads, and short‑circuit scenarios, ensuring that the time‑current characteristic matches the thermal and electrical limits of cells, busbars, and switching devices. - Implement robust trigger control
The trigger terminal must be driven according to the manufacturer’s recommended circuit, with attention to isolation, noise immunity, and fail‑safe behavior so that unintended opening or failure to open is avoided. - Consider redundancy and diagnostics
Use the three‑terminal fuse as part of a redundant protection chain, and where possible monitor its status via the BMS so that opened devices can be detected and handled at system level (for example locking out charging until service). - Plan thermal and mechanical layout
Place the fuse in a location that minimizes hot spots and mechanical stress, while ensuring accessibility and clear routing of main and trigger connections in the pack layout. - Follow datasheet guidance for standards compliance
Align your implementation with the application notes and standards references provided by SCHURTER, particularly when designing systems that must meet UL and other regulatory requirements.
Source
This article is based on information provided in SCHURTER’s official press release on intelligent fuse solutions for battery systems and the associated STTP product documentation, interpreted and structured for design engineers and component purchasers.
