Sampling Loop Impedance on Long Modules

In the design of Tesla modules, we have seen a common issue with centralized BMS, which is the impact of the length and combination method of this sampling line on sampling accuracy. This module is very long, and overall, FPC has relatively thin lines to consider cost. This impedance difference still objectively exists.



From the perspective of equivalent circuits, under different operating states, each link in the sampling loop may cause sampling accuracy deviation. In long modules, two important differences are the loop impedance and AFE leakage current.



In the circuit impedance of the battery module, it is mainly composed of the module part and the BMU circuit part



R module part: mainly includes the internal resistance of the battery cell+busbar resistance (now seen as DCR for large capacity), sampling circuit fuse, bonding line+FPC impedance sum (single is milliohms) R BMS part: sampling channel series resistance and equivalent resistance inside the AFE chip. This filtering resistance is often considered from 100 ohms to kiloohms, mainly used to match the filtering capacitor.