AN3395 Datasheet, PDF (1/11 Pages) STMicroelectronics – Sensing resistor selection and usage

AN3395
Application note
Sensing resistor selection and usage
in STC310x battery monitoring applications
Introduction
Voltage measurement and coulomb counting are the two most common methods used to
implement battery monitoring for gas gauge applications. Although the use of voltage
measurement has been a popular method, it does not produce the most accurate results.
The STC310x series battery monitor ICs developed by STMicroelectronics combine the two
methods into one integrated solution. It updates the battery State-of-Charge (SOC) at light
load (relaxation/standby period) with the real battery Open-Circuit-Voltage (OCV) while
using coulomb counting to track the battery capacity under heavy load to provide the most
accurate SOC value under all application conditions.
In coulomb counting, the sensing resistor is used to measure the battery current. The
specified maximum voltage drop on the sensing resistor is only 80 mV, thus it plays an
important role in the gas gauge accuracy and merits careful attention. This document
describes:
■ the sensing resistor (Rcg) selection
■ the Rcg power considerations
■ the Rcg layout recommendations
December 2011
Doc ID 018779 Rev 1
1/11
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