BQ40Z50-R1 datasheet(43/55 Pages) TI1

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bq40z50-R1

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SLUSCB3 – JULY 2015

11 Layout

11.1 Layout Guidelines

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-R1 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.

Figure 43. Separating High- and Low-Current Sections Provides an Advantage in Noise Immunity

Figure 44. Avoid Close Spacing Between High-Current and Low-Level Signal Lines

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.

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