IN Brief:
- The SM91572AL combines a battery-management signal transformer and common-mode chokes in one package.
- It supports daisy-chain and isoSPI interfaces used by battery-monitoring ICs from ADI, NXP, and Texas Instruments.
- Integration reduces external magnetics and PCB area while retaining a 1,000VDC working-voltage rating.
Bourns has introduced an AEC-Q200-qualified signal transformer that integrates common-mode filtering for isolated communications inside automotive and stationary battery-management systems.
The SM91572AL is designed for daisy-chain and isoSPI links between battery-monitoring devices, with support for IC families including Analog Devices LTC681x and LTC6804-1 products, NXP MC33771 and MC33772 devices, and Texas Instruments BQ79616 systems.
Functional isolation is specified with a working voltage of 1,000VDC and a dielectric withstand rating of 3,000VAC. By incorporating common-mode chokes into the same magnetic component, the device reduces the number of external parts required around the communications interface.
Primary inductance spans 150µH to 450µH, while maximum leakage inductance is 0.5µH and interwinding capacitance is limited to 20pF. The transformer has a 1:1 turns ratio and insertion loss specified at no more than 0.25dB at 4MHz.
Common-mode rejection is rated at 35dB from 1MHz to 100MHz and 28dB between 100MHz and 200MHz. Operation extends from −40°C to 125°C, covering the wide temperature range encountered within vehicle and stationary battery installations.
The surface-mount package measures approximately 8.1mm by 6.9mm and stands about 6mm high. Moisture sensitivity is rated at level one, easing storage and reflow handling during automotive electronics production.
Removing separate common-mode chokes can reduce PCB area, component placement, and routing transitions. The complete interface still requires termination, transient protection, controlled isolation spacing, and validation against the wiring, connectors, and electromagnetic environment of the finished pack.
High-voltage battery systems distribute monitoring ICs across several modules, each operating at a different electrical potential. Cell voltage and temperature data must pass reliably through the chain to the central controller, which uses the measurements for balancing, charging limits, fault detection, and contactor control.
Battery communications share space with high-energy switching
Traction inverters, DC-DC converters, chargers, pumps, contactors, and busbars generate fast electrical transients close to the low-level monitoring network. Common-mode currents can couple through parasitic capacitance and cable geometry, while impedance discontinuities can distort the differential data signal.
The integrated chokes impede common-mode energy without intentionally attenuating the differential communications path. Their inclusion within the transformer creates a more defined magnetic interface, although PCB layout and cable symmetry still determine how much unwanted common-mode energy is converted into differential interference.
Battery measurement is also becoming more digital. Current sensors combining magnetic measurement with digital transmission are being used to preserve signal integrity around high-power inverters, while isolated battery links face the same pressure to maintain dependable data in a noisy environment.
AEC-Q200 qualification establishes environmental and reliability testing for the passive component, but it does not qualify the final communications channel. Transformer tolerances, termination networks, cable length, connector impedance, IC drive strength, and node count must be assessed as one electrical system.
Working voltage must likewise be considered separately from dielectric test voltage and system-level insulation requirements. Creepage, clearance, pollution degree, altitude, transient category, enclosure construction, and applicable safety standards determine whether the complete assembly provides adequate isolation.
Placement within the battery pack influences long-term behaviour because nearby cells, busbars, contactors, and power electronics can elevate local temperature. Although the transformer carries signal energy rather than traction power, heat affects winding resistance and insulation ageing over the vehicle or storage-system lifetime.
Manufacturing traceability extends beyond the magnetic component. Battery production increasingly links cell, interconnect, sensor, firmware, calibration, and process records, allowing failures or unusual measurements to be traced through both the electrical design and its manufacturing history.
Daisy-chain architectures reduce wiring and the number of isolated interfaces, but a fault can interrupt communication with several downstream devices. Diagnostic coverage, bypass behaviour, fault localisation, and the controller response to missing data therefore require attention at the system-architecture stage.
Higher-voltage vehicle platforms and large stationary packs are increasing the number of monitored channels, the length of communications paths, and exposure to switching transients. Integrating two commonly paired magnetic functions reduces component count, while the specified isolation and high-frequency characteristics provide a defined starting point for channel design.
The SM91572AL does not eliminate the surrounding EMC and insulation work, but it consolidates part of that interface into one qualified component. Pack reliability will continue to depend on treating the transformer, termination, wiring, protection, and monitoring ICs as a single communications path.