SLUSBS8B December 2013 – November 2019 BQ40Z50
PRODUCTION DATA.
A battery fuel gauge circuit board is a challenging environment due to the fundamental incompatibility of high-current traces and ultra-low current semiconductor devices. The best way to protect against unwanted trace-to-trace coupling is with a component placement, such as that shown in Figure 43, where the high-current section is on the opposite side of the board from the electronic devices. Clearly this is not possible in many situations due to mechanical constraints. Still, every attempt should be made to route high-current traces away from signal traces, which enter the BQ40Z50 directly. IC references and registers can be disturbed and in rare cases damaged due to magnetic and capacitive coupling from the high-current path. Note that during surge current and ESD events, the high-current traces appear inductive and can couple unwanted noise into sensitive nodes of the gas gauge electronics, as illustrated in Figure 44.
Kelvin voltage sensing is extremely important in order to accurately measure current and top and bottom cell voltages. Place all filter components as close as possible to the device. Route the traces from the sense resistor in parallel to the filter circuit. Adding a ground plane around the filter network can add additional noise immunity. Figure 45 and Figure 46 demonstrates correct kelvin current sensing.