BQ27546-G1 Datasheet, PDF (30/38 Pages) Texas Instruments – nullSingle-Cell Li-Ion Battery Fuel Gauge

bq27546-G1
SLUSC53A – MAY 2015 – REVISED DECEMBER 2015
12 Layout
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12.1 Layout Guidelines
12.1.1 Sense Resistor Connections
Kelvin connections at the sense resistor are as critical as those for the battery terminals. The differential traces
should be connected at the inside of the sense resistor pads and not 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
or 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.
12.1.2 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.
12.1.3 High-Current and Low-Current Path Separation
NOTE
For best possible noise performance, it is 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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