BQ27532-G1 Datasheet, PDF (27/35 Pages) Texas Instruments – Battery Management Unit Impedance Track Fuel Gauge

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10 Layout
bq27532-G1
SLUSBU6B – SEPTEMBER 2014 – REVISED JANUARY 2016
10.1 Layout Guidelines
10.1.1 Sense Resistor Connections
Kelvin connections at the sense resistor are just as critical as those for the battery terminals themselves. The
differential traces should be connected at the inside of the sense resistor pads and not anywhere along the high-
current trace path to prevent false increases to measured current that could result when measuring between the
sum of the sense resistor and trace resistance between the tap points. In addition, the routing of these leads
from the sense resistor to the input filter network and finally into the SRP and SRN pins needs to be as closely
matched in length as possible else additional measurement offset could occur. It is further recommended to add
copper trace or pour-based "guard rings" around the perimeter of the filter network and coulomb counter inputs to
shield these sensitive pins from radiated EMI into the sense nodes. This prevents differential voltage shifts that
could be interpreted as real current change to the fuel gauge. All of the filter components need to be placed as
close as possible to the coulomb counter input pins.
10.1.2 Thermistor Connections
The thermistor sense input should include a ceramic bypass capacitor placed as close to the TS input pin as
possible. The capacitor helps to filter measurements of any stray transients as the voltage bias circuit pulses
periodically during temperature sensing windows.
10.1.3 High-Current and Low-Current Path Separation
For best possible noise performance, it is extremely important to separate the low-current and high-current loops
to different areas of the board layout. The fuel gauge and all support components should be situated on one side
of the boards and tap off of the high-current loop (for measurement purposes) at the sense resistor. Routing the
low-current ground around instead of under high-current traces will further help to improve noise rejection.
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