For longer daisy chain cable lengths or highly noisy applications, the system may require the use of transformer isolation to provide the most robust form of communications. This design choice allows the daisy chain communications to be galvanically isolated and withstand higher sources of noise compared to capacitive coupled communications. The recommendation is to use a certain set of parameters to meet automotive qualified temperature, voltage, and reliability ratings. The recommendation is to choose parts that remain in the 150 – 600uH inductance range for best performance. Table 5-1 is a list of recommended part numbers that were tested using the bq7961X devices. Choosing a part outside of this list or parameters would require thorough validation on the system designer side to ensure that the communication is robust over temperature, can withstand rapid communication transactions, and provides proper EMI filtering. Note that it is important and highly recommended to use the same transformer part number on both sides of a daisy chain interface (COML of top device and COMH of connected lower device).

Figure 5-1 Transformer Isolation Across PCBs