Issue link: https://resources.mouser.com/i/1442856
| 22 | Figure 4 Top: BMS Transformer with Center Top Capacitor and Resistor. Bottom: Image of SPI Signal. Figure 5 Bourns® Model SM91501AL Transformer on Bourns' BMS Deonstration Board Although BMS ICs have balanced currents on their I/O pins, most manufacturers recommend a center-tapped transformer. These have been found to improve Common Mode Noise Rejection (CMNR) if a filter capacitor and termination resistor are used, (Figure 4). Bourns® BMS Transformer Safety Features The windings inside the Bourns® Model SM91501AL transformer use enameled fully insulated wire (FIW) that passes the dielectric strength (Hi-POT) test of 4.3kV (1 mA, 60 seconds). Per Table 2N of IEC 60950, the minimum creepage distance for material group I, pollution degree 2 of functional insulation for a working voltage of 1600V is 8mm. The Bourns® Model SM91501AL transformer data sheet shows a minimum 10 mm creepage distance. This is because the actual tracking distance over the transformer's surface and chokes has been calculated at 10.4 mm in the samples measured. The replacement test for IEC 60950 (IEC 62368-1), which becomes mandatory in June 2019 for audio/video, information technology, and communication equipment will recognize FIW in the future. The use of FIW might qualify the device as having reinforced insulation with a lower working voltage (depending on the standard) of approximately 800V. This might allow the device to meet UL listing requirements and enable its use in additional applications such as consumer energy storage, which mandate reinforced insulation. Recommended Electrical Characteristics Some IC manufacturers' recommended primary inductance values will depend on the voltage of the communication signals, the pulse widths, and the frequency. Bourns designed its Model SM91501AL transformer with a primary inductance span between 150µH and 450µH over an operating temperature range of -40°C to +125°C. The inductance is directly proportional to the permeability of the core. The permeability of the ferrite core of a transformer is temperature-dependent and tends to increase with temperature. Therefore, the Bourns model's primary inductance will drift up toward 450µH at the upper end of the temperature range. This is the reason for the large variation in the inductance value, as specified on the data sheet. The BMS IC and transformer's noise immunity can be evaluated using a bulk current injection (BCI) test. The BCI test injects current into the twisted pair lines at set levels over a frequency range of 1MHz to 400MHz with the bit error