OEM&Lieferant Ausgabe 1/2020

83 SM91051AL transformer with a primary in- ductance span between 150 μH and 450 μH over an operating temperature range of -40 ˚C to +125 ˚C. Since inductance is directly proportional to permeability of the core, the permeability of a transformer’s ferrite core is temperature-dependent, and tends to in- crease with temperature. Therefore, the pri- mary inductance of the Bourns transformer cited will increase to approximately 450 μH at the upper end of the temperature range. This demonstrates why there can be large varia- tions in inductance values that suppliers spec- ify on their datasheets. Evaluating the noise immunity of the BMS IC and transformer can be done with a bulk current injection (BCI) test. The BCI test in- jects current into the twisted-pair lines at set levels over a frequency range of 1 MHz to 400 MHz with the bit error rate being mea- sured. A 40 mA BCI test level is sufficient for most industrial applications, where a higher 200 mA test level typically needed for auto- motive BMS designs. Ensuring Reliable Isolated BMS Communications Alongwith increased demand and subsequent growth for Li-Ion battery power, Battery Management Systems with reliable isolated communications are expected to be an im- portant part of the safety and security of the energy system. An effective BMS is an essen- tial design element that will help increase the lifespan of Li-Ion cells and contribute to en- hanced safe operation for end users. For high-voltage BMS designs, it is essential to specify transformers with the elevated working voltages of 1600 V and 1000 V as well as those with ideal inductance values of 150 μH and 450 μH over an operating tem- perature range of -40 ˚C to +125 ˚C to match higher voltage BMS requirements. In addition to enhance the safety features of the BMS, it is important to select a transformer designed with insulation that complies with IEC60664. Doing so further increases the electrical insu- lation protection from overvoltage transients making them ideal solutions for isolated BMS communications in automotive, industrial and consumer energy storage applications. References: NASA, Jeevarajan, Judith A., Safety Limitations Associated with Commer- cial 18650 Lithium-ion Cells presented at Lith- ium Mobile Power and Battery Safety 2010, Boston, MA Bourns www.bourns.com Website A BMS transformer with a centre tap capacitor and resistor can improve Common Mode Noise Rejection. Figure 2 Bourns Model SM91051AL and SM91052AL transformers have been evaluated by BMS IC manufacturers for auto- motive-grade applications and have successfully passed requirements for BCI. WE TEST FOR YOU. TEST US OUT. Our comprehensive quality services for physical and software testing ensure that you receive holistic testing and validation solutions tailored to your individual needs. FORMEL D. GLOBAL PARTNER FOR VEHICLE, PARTS AND SERVICE READINESS.